1829
Jons Berzelius discovers a new element, thorium, in samples sent to him by the Reverend Hans Esmark. Thorium will later be found to be somewhat abundant in the Earth’s crust.

1896
Henri Becquerel discovers that pitchblende, an ore containing uranium, causes a photographic plate to darken.

1897
J.J. Thomson discovers the first subatomic particle, the negatively-charged electron. This is the first indication that atoms have internal structure. He later proposes the “plum-pudding” model of the atom, with electrons dispersed in diffuse positive matter. This simplistic model explains why atoms can have no net charge even though they are composed of charged materials.

1898
Marie Curie and G.C.Schmidt independently discovered that thorium and its compounds are radioactive. M. Curie found higher than expected activity in some minerals containing uranium and thorium.

Pierre and Marie Curie isolate polonium and radium from pitchblende. Both are later found to be products from the decay of uranium.

1905
Albert Einstein describes the equivalence of mass and energy through his equation E = mc2.

1909
Hans Geiger and Ernest Marsden, under the direction of Ernest Rutherford, bombard gold foil with alpha particles (ionized helium nuclei) and observe that while most pass right through to a detector on the other side, a small fraction of the alpha particles (1 in 8000) are totally deflected backward. The result was completely unpredicted, prompting Rutherford to later comment “It was almost as incredible as if you fired a fifteen-inch shell at a piece of tissue paper and it came back and hit you”.

1911
Rutherford concludes that the “plum-pudding” model of the atom must be wrong, and that the gold-foil experiments indicate that the positive charge of the atom must be concentrated at the center. He concluded that the atom is mostly empty space, with most of the mass concentrated in a tiny nucleus and electrons being held in orbit around it by electrostatic attraction.

1913
Niels Bohr introduces his “planetary” model of the atom, with electrons “orbiting” the central positively-charged nucleus. The model, while overly simplistic, is an important step forward in the understanding of atomic structure.

1918
Rutherford proposes the existence of another subatomic particle, the positively-charged proton. He noticed that when alpha particles were shot into nitrogen gas, scintillation detectors showed the signatures of hydrogen nuclei. Rutherford determined that the only place this hydrogen could have come from was the nitrogen, and therefore nitrogen must contain hydrogen nuclei. He thus suggested that the hydrogen nucleus, which was known to have an atomic number of 1, was an elementary particle. The existence of the proton as a fundamental particle shows a basic problem with his atomic model—why is it stable? The positive charges should repel one another, and the nucleus should be torn apart by electrostatic repulsion.

1932
Walther Bothe and Herbert Becker in Germany, Irene and Frederic Joliot-Curie in France, and James Chadwick in the United Kingdom conduct a series of experiments which culminate in Chadwick’s discovery of the other subatomic particle, the neutrally-charged neutron. Chadwick later earns the 1935 Nobel Prize for the discovery. Hans Bethe later refers to the discovery of the neutron as the historical beginning of nuclear physics since it paves the way for a true understanding of the nucleus and the forces that bind it.

1932
John Cockcroft and Ernest Watson produce new elements by bombarding elements with protons.

1933
September 12. In a flash of inspiration, Leo Szilard first imagines the concept of a “chain reaction” while waiting for traffic lights to change on a street in England. Knowing that beryllium can be made to emit two neutrons when struck by one, he tries to create a chain reaction using beryllium (a stable element) but fails. He is keen to find a material that emits more neutrons and energy after it is struck by a neutron. The next year he files for a patent on the concept.

1935
Hideki Yukawa of Japan publishes his theories on mesons, which he postulates are the particles that generate the “strong nuclear force” that binds the protons and neutrons of the nucleus together. The strong nuclear force is the basic mechanism that permits nuclear stability even in the face of electrostatic repulsion between the protons.

1935
Enrico Fermi discovers that many more nuclides can be created by bombarding elements with neutrons instead of protons.

1938
December. Otto Hahn and Fritz Strassmann discover that uranium bombarded with neutrons produces elements with roughly half the original mass of the uranium. Lise Meitner, a Jewish scientist who had fled to Sweden, correctly identifies that the source of the new elements is the fission of the uranium nuclei.

1939
August 2. Szilard drafts a letter for Albert Einstein to write to President Franklin Roosevelt of the United States, warning him of German research in fission reactions, the possibility of a chain reaction and the possibility of building a nuclear bomb.

1940
March. Two German emigrés, Otto Frisch and Rudolf Peierls, in Birmingham. England, calculate that an atomic weapon only needed a few pounds of uranium-235 and might be practicable.

1941
February 23. Glenn Seaborg and his team at Berkeley Laboratory, having bombarded uranium (element 92) with deuterons, discover that it has formed two new elements, element 93, which they call neptunium, and element 94, which they call plutonium.

1941
March 28. Seaborg’s team, having produced a half-microgram of plutonium in the Berkeley cyclotron, bombards it with neutrons and discovers that it is fissile. The significance of this discovery is that plutonium and uranium are chemically different, and that plutonium, once formed in a reactor, can be chemically isolated from the uranium from which it is formed. The natural isotopes of uranium, 235 and 238, are chemically identical and can only be separated by complicated, energy-intensive processes. The realization that plutonium is fissile leads to the decision to produce plutonium for nuclear weapons.

October 9. Roosevelt authorizes the development of a new weapon based on atomic fission.

December 7. The US Pacific Fleet is attacked at Pearl Harbor, Hawaii, plunging the United States into World War II.

1942
February. Glenn Seaborg becomes curious whether thorium-232, a naturally-occurring element with a half-life of 14 billion years, can be transmuted into a fissile isotope. He instructs John Gofman and Raymond Stoughton to bombard thorium-232 with neutrons at the Lawrence Berkeley Laboratory cyclotron. They discover that the thorium-232 will absorb a neutron to form thorium-233, which then rapidly decays into protactinium-233. The protactinium-233 wil
l then decay (with a 27-day half-life) into uranium-233, which they discover is fissile (both with slow and fast neutrons) and emits more than 2 neutrons per absorption. The full implications of these discoveries take several years to comprehend, but these scientists had essentially discovered that it was possible to build self-sustaining nuclear reactors (both thermal and fast) that run on thorium, the most common radioactive element on Earth (more common than lead and four times more common than uranium).

December 2. A controlled nuclear fission reaction is created for the first time at the University of Chicago by a team lead by Enrico Fermi. Chicago Pile-1, as the reactor is called, is formed from solid spheres of natural (unenriched) uranium moderated in ultra-pure graphite. The reaction is sustained for 28 minutes. The reactor, although critical, produces almost no thermal energy, only about ¼ of a watt.

1943
October. Construction begins on the first plutonium production reactor at the Hanford site, the B-reactor. The B-reactor was moderated by graphite, cooled by water, and had operating regimes where it had a positive temperature coefficient of reactivity. This fundamental danger was understood but the importance of the reactor was such that it was deemed secondary to the threats of war and the need for plutonium production for atomic bombs.

September 26. The B-reactor goes critical for the first time and plutonium production begins at the Hanford site.

September 28-29. The B-reactor, as the first nuclear reactor to operate at any significant power level (9 megawatts) is also the first to experience the “poisoning” effects of xenon-135, a gaseous product of fission with an enormous appetite for neutrons. The generation of Xe-135 causes the power level in the reactor to fall from 9 MW to 0.2 MW. The problem is “solved” thanks to the over-engineering of the reactor, which allows the operators to load more fuel in the reactor and compensate for the poisoning effect of the Xe-135. If not for the conservative design of the reactor, the “xenon” scare could have ended the production of plutonium for the war in the B-reactor. Xenon poisoning will be a basic problem in all solid-core reactors henceforth, limiting their abilities to operate at large scales and at high flux levels. Xenon poisoning will be found to be essentially absent from fluid-fuel reactors since the xenon, as a gas, comes out of solution during the pumping of the fluid fuel.

December 17. D-reactor goes critical at Hanford, further increasing plutonium production capability.

December 26. The first slugs of natural uranium irradiated in the B-reactor by neutrons are dissolved in the separation facility at Hanford to extract their plutonium. The short exposure duration has produced little plutonium-239 in the uranium, but additional exposure must be avoided to prevent the generation of other isotopes of plutonium (Pu-240, Pu-241) in the fuel. The enormous amounts of uranium that must be irradiated and processed to extract a very small amount of plutonium is a basic consequence of using a thermal-spectrum reactor to generate weapons-grade plutonium. Plutonium production and plutonium extraction will ultimately result in the generation of millions of gallons of liquid high-level nuclear waste at Hanford. The generation of large amounts of liquid high-level waste as a result of reprocessing will also be a significant problem for the solid-core commercial descendants of the Hanford reactors.

1945
February 5. Plutonium produced and separated at Hanford is shipped to Los Alamos to build the “Gadget” bomb used in the Trinity test and the “Fat Man” bomb used over Nagasaki.

February 25. F-reactor goes critical at Hanford, further increasing plutonium production capability.

May 9. Nazi Germany surrenders to the Allied powers, marking the end of World War II in Europe. Many of the scientists on the Manhattan Project, assuming that their work is primarily directed against Hitler, are surprised to find out that the US intends to go forward with the development of the atomic weapons for use against Japan.

July 16. An atomic bomb nicknamed “Gadget” is detonated at a site in the Jornada del Muerto (Journey of Death) desert of New Mexico in an event that is later called “Trinity.” The bomb is based on weapons-grade plutonium produced at the reactors in Hanford, Washington. It has a yield of 20,000 tons of TNT, significantly in excess of predictions. The “implosion” type bomb is later used at Nagasaki and implosion-type devices later become the most common type of nuclear weapons.

July 26. The United States, Great Britain, and China issue the Potsdam Declaration, demanding the immediate and unconditional surrender of Japan and the disarmament of their military.

August 6. An atomic bomb, using highly-enriched uranium and code-named “Little Boy”, is dropped on the Japanese port city of Hiroshima by the American B-24 bomber “Enola Gay.” The bomb detonates at 15,000 feet altitude and kills over 80,000 people. President Truman announces the existence of the atomic weapon program and warns Japan: “We are now prepared to obliterate rapidly and completely every productive enterprise the Japanese have…It was to spare the Japanese from utter destruction that the ultimatum of July 26 was issued at Potsdam. Their leaders promptly rejected that ultimatum. If they do not now accept our terms they may expect a rain of ruin from the air, the like of which has never been seen on earth.”

August 9. Another atomic bomb named “Fat Man”, based on an implosion design and using weapons-grade plutonium, is dropped on the Japanese city of Nagasaki by the American bomber “Bock’s Car.” The bomb detonates at 15,000 feet altitude and kills over 40,000 people.

August 14. Japan unconditionally surrenders to the Allied powers, ending World War II.

1946
April 10. Alvin Weinberg and Forrest Murray write a paper called “High-Pressure Water as a Heat Transfer Medium in Nuclear Power Plants” proposing what would become the light-water reactor. Weinberg is later awarded a patent for the light-water reactor, which is the most common type of nuclear reactor in operation worldwide today. In the paper, Weinberg lists several drawbacks to the LWR concept—it is limited to rather low temperatures, the reactor must have a large, heavy pressure vessel, and that it poorly utilizes fissile resources. To mitigate this last disadvantage, he proposes that the reactor operate on a breeding cycle using thorium and uranium-233. This technique is not actually used until the thorium-U233 core is tested in Shippingport in 1977.

August 1. President Truman signs the Atomic Energy Act, forming the US Atomic Energy Commission, a civilian agency to succeed the Manhattan Project.

1947
April 3. Following an inspection of the US nuclear stockpile, the head of the AEC, David Lilienthal, reports to President Truman that the United States does not have a single operational nuclear weapon available. This shocking news is branded top-secret and is used to spur intense development of US nuclear weapons.

July 22. The experimental NRX reactor begins operation in Chalk River, Ontario, Canada. The reactor is solid-fueled, using natural uranium moderated by heavy water (water in which the normal hydrogen has been replaced by deuterium). It is a predecessor to Canada’s CANDU nuclear reactor concept, which also uses natural uranium and heavy-water as a moderator and coolant.

1951
July. Congress announces the construction of the first nuclear submarine.

Ray Briant, Vince Calkins, and Ed Bettis of ORNL first propose a reactor bas
ed on uranium fluorides dissolved in fluorides of alkali metals and alkaline-earth metals.

December. The Experimental Breeder Reactor-1, a liquid-metal-cooled, solid-core, fast-spectrum reactor is the first nuclear reactor in the United States to produce electricity, enough to power four light bulbs. The EBR-1 is heralded as the reactor of the future.

1952
June 14. The keel is laid for the USS Nautilus, the first nuclear-powered submarine.

December 12. An accident takes place at the experimental NRX reactor at Chalk River, Canada, which results in a partial meltdown of the core and severe fuel damage.

1953
December 8. In his “Atoms for Peace” speech before the United Nations, US president Eisenhower proposes to share US nuclear technology with other nations in exchange for their promise not to develop nuclear weapons.

1954
January 21. USS Nautilus is launched in Groton, Connecticut.

June 27. The Obninsk Nuclear Power Plant, in Russia, becomes the world’s first nuclear reactor for power generation, with a capacity of 5 megawatts (electric).

August 30. The Atomic Energy Act is passed by Congress directing the federal government to promote the peaceful use of atomic energy, with the understanding that disposal of the highly radioactive waste produced would be the responsibility of the federal government.

September 30. USS Nautilus commissioned.

November 3. The Aircraft Reactor Experiment, the first liquid-fluoride reactor, goes critical for the first time at Oak Ridge National Laboratory. It operates at a maximum temperature of 1600° F and at a maximum power of 2.5 megawatts (thermal). It also conclusively demonstrates the remarkable chemical and nuclear stability of the liquid-fluoride reactor concept. After 100 hours of operation it is shut down on November 11.

1955
July 17. The experimental boiling water reactor BORAX III is used to power the first US town entirely by nuclear energy—Arco, Idaho—population 1000.

November 29. The EBR-I reactor (the first reactor to produce electrical power in the US) suffers severe damage to its solid-fueled core during an accident caused by operator error.

1956
Skeptical of the benefit and practicality of the nuclear-powered aircraft, Alvin Weinberg asks the liquid-fluoride researchers to evaluate the reactor for civilian use. Weinberg convinces Kenneth Davis, the head of the Division of Reactor Development of the Atomic Energy Commission, to provide ORNL with the initial $2 million to begin a civilian liquid-fluoride reactor program.

The National Academy of Sciences recommends deep geologic disposal of the long-lived, highly radioactive wastes from nuclear reactors, suggesting that buried salt deposits and other rock types be investigated for permanent repositories.

August. The Calder Hall Unit-1 Nuclear Plant in the United Kingdom becomes the first nuclear power plant in that nation, with a capacity of 50 megawatts (electric). It is a solid-core reactor fueled by natural (unenriched) uranium. It is cooled by air and designed to produce nuclear energy as well as to generate plutonium for nuclear weapons.

1957
September 2. The Price-Anderson Act—an amendment to the Atomic Energy Act of 1954—limits the financial liability of utilities in the event of a nuclear accident. This liability restriction is essential to convincing commercial utilities to utilize nuclear power.

December 2. The Shippingport Nuclear Power Plant in Shippingport, Pennsylvania becomes the first commercial nuclear reactor in the world. It is essentially a scale-up of the pressurized water reactor used for the Nautilus, and is supported by the military as a precursor to a nuclear reactor for an aircraft carrier.

1958
July. USS Nautilus crosses under the north polar ice cap for the first time.

1959
The Fluid Fuels Reactor Task Force is convened by the AEC to assess which of the fluid-fuel reactor concepts should be continued. Each concept is a thorium breeder with a thermal neutron spectrum. The molten-salt (liquid-fluoride) reactor is chosen over the aqueous homogeneous reactor (water-based) and the liquid-metal reactor (lead and bismuth-based) for further development. The first sentence of the Summary of the Task Force Report (TID-8505) was, “The Molten Salt Reactor has the highest probability of achieving technical feasibility.”

October 15. Dresden-1 Nuclear Power Station in Illinois, the first US plant built entirely without government funding, achieves first criticality.

1960
In the early 1960s, the Atomic Energy Commission (AEC) announces that a salt mine at Lyons, Kansas, will be developed as a high-level radioactive waste repository, only to reverse its decision after state geologists discover the site is riddled with abandoned oil and gas exploration boreholes.

The focus of the Molten-Salt Reactor Program at ORNL gradually shifts from a high-conversion reactor to a breeder. The gain from thorium breeding is slight compared to a plutonium-fueled fast reactor, so special emphasis is put on rapid, online reprocessing of salts to minimize neutron losses to fission products. Such a capability is essentially impossible in a solid-core reactor.

Spring. ORNL submits a proposal to the AEC to build a demonstration liquid-fluoride reactor that reflects their latest design understanding. It would be graphite-moderated and use lithium and beryllium fluorides as the solvent.

Summer. The ORNL proposal for the “Molten Salt Reactor Experiment” is accepted and design of the reactor begins.

1961
Dr. Mieczyslaw Taube of the Institute of Nuclear Research in Warsaw, Poland, publishes a paper examining the feasibility of using a reactor based on liquid chloride salts to achieve a fast neutron spectrum, possibly allowing a liquid-salt reactor to operate on the uranium-plutonium breeding cycle so popular at the time.

1962
L.G. Alexander of ORNL also suggests (ANL-6792) a liquid-salt reactor that uses chlorides instead of fluorides to achieve a fast neutron spectrum.

September 16. The Indian Point-1 nuclear reactor begins operating at Buchanan, New York. Designed and built by Babcock and Wilcox for Consolidated Edison, it is a pressurized water reactor designed to produce 275 MW of electricity. Unlike other pressurized-water reactors, the Indian Point-1 reactor uses highly-enriched uranium as a fuel and thorium as a fertile material. This combination has a superior conversion ratio in a thermal neutron spectrum than low-enrichment uranium (more thorium is bred to uranium-233 than uranium-238 is bred to plutonium-239). The uranium-233 generated in the Indian Point reactor is later processed into a tetrafluoride and used to fuel the Molten-Salt Reactor Experiment.

1963
April 10. The nuclear submarine USS Thresher is lost at sea with all hands (128).

August 23. The Enrico Fermi Fast Breeder Reactor goes critical for the first time. The reactor is a 60 MWe, sodium-cooled, fast-spectrum reactor designed to breed more plutonium-239 than it consumes. It is initially fueled with highly-enriched uranium but it is anticipated that future LMFBRs will be fueled with plutonium bred in these reactors.

1965
June 1. The MSRE goes critical for the first time, using a fuel of 20% enriched uranium tetrafluoride in a combination of lith
ium and beryllium fluoride. The reactor contains no thorium fluoride but includes some zirconium fluoride to “mop-up” any oxygen that might make its way into the core.

1966
May 23. After about a year of experimentation, the MSRE reaches its full power rating of 8 megawatts (thermal).

October 5. The Enrico Fermi Fast Breeder Reactor suffers extensive core damage and melting when a piece of metal comes loose in its core and blocks the flow of sodium coolant to some of the fuel rods. Starved of coolant, the solid rods begin to melt and slump. No radiation escapes the containment but the core is heavily damaged and the reactor is shut down for nearly four years. The incident was the basis for a controversial book by John Fuller entitled “We Almost Lost Detroit.” Such an accident is impossible in the design of a liquid-salt reactor since any flow blockage in the core would lead to a decrease in temperature (since the fluid is the fuel, rather than the coolant) rather than an increase.

1968
May 22. The nuclear submarine USS Scorpion is lost at sea with all hands (128).

August 23-29. The uranium fuel is removed from the core salt of the MSRE by fluoridation to gaseous uranium hexafluoride. This demonstrates, in actual operation, the simple technique of fluoridation to remove fuel from the salt of the reactor. The uranium, once separated from the intensely radioactive fission products, is safe enough to handle without protection.

October 2. The MSRE goes critical for the first time on uranium-233, becoming the first (and only) nuclear reactor to operate on uranium-235, uranium-233, and plutonium-239, demonstrating the remarkable flexibility of the liquid-fluoride reactor concept.

1971
June 4. President Richard M. Nixon announces a national goal of completing the Liquid Metal Fast Breeder unit by 1980, the reactor that would later be called the Clinch River Breeder Reactor.

1972
September. An “evaluation” of the molten-salt breeder reactor concept is released by the Division of Reactor Development and Technology of the AEC in response to a request from the Office of Science and Technology (WASH-1222). Although it contains no overt recommendations about MSR research, it essentially ignores all of the beneficial safety and performance advantages of the MSR over solid-core reactors (especially the LMFBR) and accentuates the problems uncovered during the operation of the MSRE, such as tellurium cracking and tritium generation. It also emphasizes the AEC’s preference for the LMFBR and the cost difficulties of funding two totally different approaches to breeder reactors (fast-spectrum uranium-plutonium vs. thermal-spectrum thorium-uranium).

November. The decision is made to decommission the Fermi fast breeder reactor, marking an end to the first attempt in the US to build a commercial fast breeder reactor.

1973
January. ORNL is directed by the AEC to terminate all development of the molten-salt reactor.

June 29. President Nixon proposes to split the Atomic Energy Commission into the Energy Research and Development Administration (ERDA) and the Nuclear Regulatory Commission (NRC).

The first French power plant based on the liquid-metal fast breeder reactor, named “Phenix”, achieves criticality. It has a power rating of 250 MWe.

US utilities order 41 nuclear power plants, a one-year record. But thereafter, no reactor ever ordered was completed to operation. The final reactor completed from the 1973 order was the Watts Bar-1 plant in Tennessee, which achieved criticality in 1996.

1974
January 31. The Fort St. Vrain power plant goes critical for first time. Manufactured by General Atomics, it is a high-temperature gas-cooled reactor (HTGR), with a graphite-moderated core and helium coolant. In addition to being the first commercial large-scale gas-cooled reactor, the nuclear material in the core consists of thorium as a fertile material and highly-enriched uranium (>93% U-235) as the fuel. The reactor is designed to achieve significantly high conversion ratio for a commercial reactor—about 0.8, but still not enough to breed. General Atomics intended to build a new fuel cycle based on thorium and highly-enriched fuel that never took off after Fort St. Vrain became an economic failure. It was permanently decommissioned in 1989, after a history of operation where it was only available about 14% of the time (compared with ~90% of typical nuclear plants).

May. India detonates a nuclear weapon built from plutonium separated from natural uranium irradiated in a heavy-water reactor similar to the US reactors built at Hanford.

October 11. President Gerald Ford abolishes the Atomic Energy Commission and creates in its place the Energy Research and Development Administration (ERDA) and the Nuclear Regulatory Commission (NRC) to begin regulating the nuclear industry. The Joint Congressional Committee on Atomic Energy (JCAE) is also abolished.

1975
The Energy Research and Development Administration (formerly AEC) begins to search for a possible permanent repository for the nation’s nuclear waste. A multiple site survey emphasizing buried salt deposits and federal nuclear facility sites is conducted in 36 states, including Nevada, but is reduced in scope due to decreased funding and political opposition from states.

ORNL is again directed by the AEC to end all work on the molten-salt reactor, “for budgetary reasons.”

October. President Ford, acting under campaign pressure from Jimmy Carter, bans the reprocessing of nuclear fuel, based on fears of proliferation of nuclear material for weapons.

1977
April 7. President Jimmy Carter announces a new policy banning reprocessing of used nuclear fuel.

August 4. President Carter combines the Energy Research and Development Administration (ERDA) with the Federal Energy Administration (FEA), creating the Department of Energy (DOE).

August 26. An experimental thorium-uranium-233 core is loaded in the Shippingport Atomic Power Station to test the use of thorium fuel in conventional pressurized-water reactors. The core runs for five years and is then removed and examined. The examination shows that there is 1.3% more fissile material in the core than when the experiment began, showing that thorium can be successfully bred into uranium-233. Unfortunately, no additional light-water reactors are converted to “light-water breeder reactors.”

1979
March 28. The second unit at the Three Mile Island Nuclear Power Plant suffers a partial core meltdown when the water coolant is accidentally drained from the core of the reactor. Without cooling from the water, the decay heat from the fission products in the fuel rods leads to a temperature increase that causes the fuel to melt and bow. Gaseous fission products (krypton and xenon) are released from the fuel and later vented to the environment. There is a tremendous fear that a bubble of hydrogen and oxygen gas, formed from the dissociation of water, is present in the reactor vessel and might recombine and explode, damaging the containment, but this is later mitigated. The reactor is never restarted. No fatalities or excess cancers are ever directly tied to the accident but it becomes a rallying cry for the anti-nuclear movement. A liquid-salt reactor that is designed to passively drain its core is impervious to a loss-of-coolant accident, even intentional or malicio
us.

1981
October 8. President Ronald Reagan lifts the ban on commercial reprocessing, but the development of reprocessing facilities was no longer considered economically viable in the United States.

1983
January 7. President Reagan signs into law the Nuclear Waste Policy Act.

October 26. Funding for the Clinch River Breeder Reactor project is killed by Congress.

1986
April 26. Unit-4 of the Chernobyl Nuclear Power Plant is heavily damaged during a safety experiment in Pripyat, Ukraine. The reactor, poorly designed with no containment and operation regimes with positive temperature coefficients of reactivity, in nonetheless used in a “safety” drill that involved the intentional deactivation of most of the automatic safety systems. The accident is not only far worse than Three Mile Island, but substantially different in that it was caused by a runaway nuclear reaction rather than the loss of coolant to remove the decay heat generated by fission products. During the accident, the reactor power jumped to ten times the normal operational output, causing the fuel rods to melt and the water coolant to vaporize to steam. The steam pressure caused an explosion which ripped off and destroyed the reactor lid, ruptured the coolant tubes and blew a hole in the roof. To reduce costs, and because of its large size, the reactor was constructed with only partial containment. This allowed the radioactive contaminants to escape into the atmosphere after the steam explosion burst the primary pressure vessel. After part of the roof blew off, the inrush of oxygen—combined with the extremely high temperature of the reactor fuel and graphite moderator—sparked a graphite fire. This fire greatly contributed to the spread of radioactive material and the ultimate contamination of outlying areas. A 2005 UN report estimates that 56 people were directly killed in the accident and that some 4000 others would suffer accident-related cancers in their lifetime. The type of accident (reactivity excursion) is not possible in a liquid-fluoride reactor that is designed with a strong negative temperature coefficient of reactivity, which is quite straightforward to generate, based on the expansion of salt with temperature.

The DOE indefinitely postpones the second repository siting program, violating the regional equity intent of the Nuclear Waste Policy Act, after much objection from states in the northern mid-west and east where potentially acceptable repository sites in granite are prohibited.

1987
Congress amends the NWPA, designating Yucca Mountain, Nevada as the sole repository site to be characterized. Two other sites are removed from consideration, the screening process for a second repository site is ended, and studies of repository sites in granite are prohibited.

1992
October 24. President George H.W. Bush signs into law the Energy Policy Act.

1994
January 14. The US signs a contract with the Russian Federation to buy highly-enriched uranium (HEU, >93% U-235) and isotopically dilute it with depleted uranium (<0.7% U-235) to form low-enrichment uranium (LEU) for light-water reactors. The “un-enrichment” the fuel effectively wastes all of the enormous energies that went into the original enrichment. It also represents another lost opportunity to use HEU as the “start charges” for a great number of liquid-fluoride reactors, that could then sustain themselves on solely on thorium.

1995
Tunnel boring machine makes progress into Yucca Mountain but encounters loose ground at various points. Five miles of tunnels are planned for the study area by 1996. Bills are pending in Congress that re-prioritize the waste program to emphasize interim waste storage and transportation, with site characterization as a lower priority.

1997
Thermal testing begins at Yucca Mountain. It is scheduled to take eight years.

March. Explosion at Tokai-Mura reprocessing facility in Japan.

1998
DOE fails to meet its January deadline for waste acceptance. Lawsuits are filed by states and the nuclear industry. Legislation that would put an interim storage facility on the Nevada Test Site dies in Congress. The Yucca Mountain Viability Assessment is released in December with DOE declaring the site “viable” but admitting that much work still needs to be done before the site can be officially recommended in 2001.

1999
September 30. Criticality accident at Tokai-Mura reprocessing facility in Japan.

2002
Spring. It is estimated that 7 billion dollars have been spent studying Yucca Mountain as a nuclear-waste repository, making it the most studied geological site in history.

Energy Secretary Spencer Abraham recommends Yucca Mountain as a suitable site to President George W. Bush. Bush approves the recommendation. Nevada Governor Kenny Guinn exercises the State’s right to veto the Yucca Mountain project. The project moves to Congress, where a simple majority in both houses is needed to overturn Guinn’s veto. Yucca Mountain is debated and passed first in the House of Representatives and then more narrowly in the Senate. President Bush signs the joint resolution into law, officially designating Yucca Mountain as the nation’s nuclear waste repository site. DOE begins work on its application for a license to build and run the repository. The Nuclear Regulatory Commission (NRC) identifies 293 technical issues DOE must solve before submitting the license application. The State of Nevada files major lawsuits against DOE, NRC, Bush, and Abraham.

2004
The US Court of Appeals in Washington, D.C. throws out the EPA’s 10,000 year radiation standard for Yucca Mountain and dismisses Nevada’s other lawsuits. The Department of Energy selects the southern Nevada Caliente corridor to build a rail line for shipping waste to Yucca Mountain (Carlin is named the alternative). Nevada files suit over the Caliente Rail Line. An NRC Board rules that DOE’s Yucca Mountain public internet database (Licensing Support Network) is incomplete. It is uncertain whether DOE will submit its license application to the NRC in December as planned. An NRC Comissioner and other officials say a 2010 opening is unlikely.

3216 metric tonnes of thorium nitrate, comprising the entirety of the US strategic reserve, is permanently buried at the Nevada Test Site. This thorium, if completely consumed in a molten-fluoride reactor, would generate 720 quads of heat energy, sufficient to power the entire United States for two years.

2005
August 8. The Energy Policy Act of 2005 is signed into law. In addition to extending the Price-Anderson liability protections until 2025, the act provides for substantial government subsidies (~$4.3 billion) for the construction of new pressurized-water reactors and the construction (at government expense) of a high-temperature, gas-cooled reactor in Idaho capable of generating the high temperatures required for thermochemical generation of hydrogen. Ironically, the liquid-fluoride reactor is also capable of generating the high temperatures needed for hydrogen production, but there is no commercial advocacy for the reactor.

For several weeks now, I have been part of an informal group of individuals interested in the prospects of thorium power for the future. Most of these folks have been up in Ohio, connected with NASA Glenn Research Center, Cleveland State University, and Battelle. A few have been at some of the DOE national labs, such as Oak Ridge and INL. And then there’s me down in Alabama.

We’ve been getting together by phone telecon and discussing what must be done to help the nation, and perhaps the world, achieve the secure energy future we all so desperately desire. This work hasn’t necessarily been part of our jobs, but it certainly has been congruent with the ideals of what research in the national interest is all about.

Well, after talking on the phone for so long, we decided that it would be a good idea to get together face-to-face. So we met in Cleveland, at the Glenn Research Center, on Thursday, May 25th. And I think it was a great meeting for all of us.

Dr. Albert Juhasz of GRC was our host and the coordinator of the meeting. We were also welcomed by a representative of GRC.

Dr. Charles Alexander of Cleveland State got us started. Chuck is a former president of the IEEE (professional society for electrical engineers) and is currently Dean of the College of Engineering at Cleveland State University. Chuck talked about the world’s needs for power, his efforts at Cleveland State to excite and encourage new students to enter the field of engineering (especially power engineering), and a new research group that has been organized at Cleveland State specifically to pursue some of these new opportunities. He spoke with zeal about the ability of engineers to conquer the problems that lie before us in the world, which was a timely message for our group and their aspirations.

Jim Werner of Idaho National Laboratory talked about the work they are doing at INL under the GNEP (Global Nuclear Energy Partnership) program. GNEP is eesentially an effort to close the nuclear fuel cycle for light-water reactors by destroying transuranic isotopes in a fast-spectrum reactor. They anticipate down-selecting on the sodium-cooled fast reactor in the next year or so. Then they anticipate building a LWR fuel reprocessing facility in 2012, a fast-spectrum reactor fuel fabrication facility in 2015, and a fast-spectrum demonstration reactor in 2018. I mentioned my concerns about achieving an acceptably negative temperature coefficient of reactivity in a fast-spectrum reactor with uncertain isotopic concentrations in the fuel elements, but Jim said that the initial reactor would run on highly-enriched uranium as a “driver” and the transuranics as a “blanket”.

Then I spoke on the value of thorium as a possible energy source. I tried to highlight the extensive nature of the thorium resource, the issues involved in using it (essentially the need for continuous reprocessing), and the several attempts at fluid-fueled reactors designed to burn thorium.

I then followed with a presentation on the history and potential of the liquid-fluoride reactor, describing its origin as a high-temperature reactor for the nuclear aircraft program, its evolution into a thorium-breeder, and its eventual demise at the hands of the AEC in an attempt to preserve the liquid-metal fast-breeder program. I talked about why it is uniquely suited to exploit the thorium resource, and why most of reasons it was previously killed would be considered selling points for the reactor today.

Chris Pestak of Battelle got the discussion going by stating, “I think the purpose of this meeting is to save the world!” We all laughed, but there was a lot of truth to the statement. I had realized, thanks to Jim Werner’s talk, that despite the best efforts of the DOE and the GNEP program over the next few decades, we would merely be “holding the line” for US nuclear power production. We would not be able to mount a major expansion of nuclear power in the US, nor in the world, because of the basic limitations of the light-water reactor and its profligate use of uranium resources. The efforts outlined under the GNEP program would have a primary goal of preventing the need for a second US high-level waste repository.

The group seemed optimistic on what we could do, even though we realized that we were not going to be changing the course of nuclear energy any time soon. “What is the plan forward?” Chris asked, and we began to discuss the possibilities that would be opened by concentrating on university-scale research. Perhaps a small fluoride research reactor could be built at a university? Cleveland State didn’t have a nuclear engineering program, but Ohio State did, and soon we were speculating how Ohio State might be able to get involved with the fluoride reactor and perhaps even build one.

Certainly building the first new fluoride reactor since the MSRE would be a powerful shot-in-the-arm for the program, and the idea was not outside the realm of reason. The ARE and MSRE were both small reactors, and TRIGA reactors have been a staple of university nuclear research programs for years. Like the TRIGA, the fluoride reactor can have a very strong negative temperature coefficient of reactivity—an absolute must for a reactor that students might be operating. It seemed reasonable to me, and helping students build and operate a real reactor could get them trained and excited for the thorium future we hoped to build.

Thorium as a basic energy source was endorsed heartily by Dr. Alexander. He said, “I haven’t heard anything today to make me think that this isn’t the way to go.” He spoke about the desireability of he and I writing a paper for the upcoming IEEE Power Conference on the subject of thorium as the energy source of the future. Someone suggested that perhaps that might “brand” us a bit, so we suggested an alternate title: “Should thorium be the energy source of the future?” In this paper we could describe the promise of thorium, the advantage of the liquid-fluoride reactor as the machine to release that energy, and the advantage of the helium gas turbine as the machine to turn that energy into electricity.

We also discussed the intriguing possibility of the submarine LFTR as a power source. Could it be done? Would it “fly” politically and socially? Ray Beach stated that he thought the issue of siting a nuclear power plant was a big problem, and everything I’ve read leads me to agree. No one wants to live next to a nuclear power plant, and no one likes big ugly power transmission lines. Considering the proximity of so much of the population to the coast, the ability to site plants offshore and out-of-sight is very appealing. I mentioned that I had recently read a book about the history of the submarine, and in the mid-1950s Admiral Arleigh Burke, Chief of Naval Operations, decided that a submarine should be an underwater Cape Canaveral for ballistic missiles. The concept was considered to be the very edge of credibility. Yet after a few years of hard intense work, technological advancement, and strong leadership, the first ballistic missile submarine went to sea. How crazy was it to imagine the submarine as an underwater power station? Now we just need an Admiral Burke…

Finally we wrapped up and headed back to our homes and
hotels after a long and productive day. I felt so much excitement about what we had talked about and the general agreement we felt. I know many of the folks in the group felt the same way. There is obviously so much more hard work to do, but if we succeed, I’m sure we will look back on this meeting as the moment when our efforts first began to coalesce.

Thermodynamics was one of my favorite subjects in school–it was elegant, compelling, and instructive about so many aspects of life. But one thing it was not was intuitive. In fact, thermodynamics can make predictions that sound downright nutty to someone who’s never heard them before. But one of the beauties of the subject is that once you learn it, you see examples all around you in daily life.

Thermodynamics is also a very important subject for those of us who want to make electricity from nuclear energy, and for the consumers of electricity out there who want to understand how their electricity is generated.

There are two basic laws of thermodynamics–the first, simply put, is that energy is always conserved. No matter what you do, the total amount of energy doesn’t change–it just changes forms. Sounds pretty good! Why are we worried about an energy crisis? If the energy never goes away, then it should all be floating around somewhere waiting for us to use it again, right?

Well, that’s where the second law of thermodynamics comes in, and it says, simply put, that energy is always degraded. So every time you change energy from one form to another, you are degrading it, and it is less useful. What does it mean to “degrade” energy? It means that you can extract less and less useful work from it, until finally you can’t extract any at all…

Work, power, energy, electricity, heat–what do they all mean? What do they have in common? Let’s quickly define them: work, heat, and electricity are all forms of energy. All work is energy, but not all energy is work. All heat is energy, but not all energy is heat (although it all gets there). Power is the rate at which energy flows–some rate of energy per unit time. So we measure the work rate of an engine in power, but you can also measure the rate at which heat energy flows in terms of power as well. Electricity is also a form of energy, which can quite easily be turned into work, and work can easily be turned into electricity. In each case, you want to turn work into electricity while turning as little into heat as possible–the inverse is true as well. It’s very easy to turn either work or electricity into heat, but rather difficult to turn heat into work or electricity.

Are you getting the idea that maybe heat isn’t the most useful form of energy? Then you’re on the right track. Heat (or thermal energy) is the energy in the random motion of molecules. It is disordered kinetic energy, the energy of motion. Work and electricity are ordered kinetic energy–all the molecules of the shaft of an engine moving the same way, or all the electrons in a wire moving the same way. It is easy to turn order into disorder (you should see my office) but more difficult to turn disorder into order.

Why worry about all this? Because with a nuclear reactor we make heat–thermal energy–and we want to turn it into work (turning a shaft) and then into electricity (the shaft turns an electrical generator). How much of the heat can be turned into electricity?

The classic engineering answer to everything–it depends. In this case, it fundamentally depends on how hot the heat source is, and how cool the “sink” the heat will be rejected to is. Whoa! What’s a heat sink? Why does it have to be cold? Well, let me cover a little ground first.

Back in the early 1800s, there was a French engineer named Sadi Carnot, who wanted to know how to make the most efficient engine he could (the one that would make the most work for a given amount of fuel). Unfortunately, Carnot didn’t have the nice convenient laws of thermodynamics to guide him. He didn’t even have a correct understanding of matter or thermal energy. Which makes his discoveries even more amazing.

Carnot used to watch waterwheels. He watched the water flow over a wheel and turn it, and the wheel would grind wheat or some other activity. Carnot imagined attaching another waterwheel to the first one, but the second wheel would lift the water back up again after it had fallen. He wondered if he could ever build a system where he could lift up more water than had fallen to drive the first wheel. Intuition says no, but he wanted to know why. Of course, we know there would be friction between the wheel bearings and so forth, but he imagined a perfect wheel with no friction, and he realized that the VERY BEST he could do would be to lift an equal amount of water as had fallen. It just couldn’t get any better than that.

Then he applied some of his reasoning to engines–how much energy could be extracted as work from heat? It turned out that even in a perfect engine, only a certain amount of energy could be extracted as directed, ordered energy from an undirected, disordered thermal energy source. He imagined a perfect engine that could do this, and unsurprisingly, that engine is still called a Carnot cycle.

It turned out that the whole answer to how much work (ordered energy) could be extracted from heat (disordered energy) depended on how how the original thermal energy source was, and how cold the sink to which the unconverted thermal energy (original thermal energy minus work energy) would be rejected. If the hot side was hot and the cold side was cold, you could extract a certain amount. The hotter the hot side, the more work could be extracted. The colder the cold side, the more work could be extracted. But between any two temperatures, there was only a certain amount of work that could be extracted, even by a perfect engine.

The equation turned out to be really simple. The fraction of work that could be extracted was one minus the sink temperature divided by the source temperature.

[latex]
begin{displaymath}
eta_{text{thermal}} = 1 – frac{T_{text{low}}}{T_{text{high}}}
end{displaymath}
[/latex]

where nth is the work fraction, T(low) is the sink temperature, and T(high) is the source temperature. Let’s say we had a perfect Carnot cycle where the high temperature side was boiling water at 100°C, and the low side was almost freezing water at 2°C. How much work could we extract? First we have to use the absolute temperature scale, measured in Kelvins. 100°C is 373 K, and 2°C is 275 K. So plugging those numbers in we get:

[latex]
begin{displaymath}
eta_{text{thermal}} = 1 – frac{275}{373} = 0.262
end{displaymath}
[/latex]

Wow–only 26% of the heat could be turned into work? That’s not very much. So we want to get the high side hotter, and the cold side colder. But let’s say, for sake of argument, that 2°C is about as cold as we can reasonably hope for on Earth. You can get colder, but the water turns to ice, and it’s much harder to reject heat to ice than to water (little problem with the flow). So let’s leave the cold side at 2°C (275 K).

We must get the hot side hotter. And getting the hot side hotter is the principle concern of the nuclear engineer. He/she wants to convert as much of the energy generated from fission to electricity, and so must get the reactor to generate the heat at as high a temperature as can be practically achieved. By accomplishing this, the reactor will make more electricity, reject less heat to the environment, and in general have superior economic performance. I’ll talk more about how to do this in some unconventional ways in an upcoming post.

For those of you who would like to understand all of this a lot better than I have explained, check out The Mechanical Universe, an excellent scientific series that explains so many physical concepts in a visual and compelling manner. Episode 46 will explain more about Carnot and his cycle. The programs can be viewed online for free after a brief registration. You’ll love it!

Chemical reprocessing of nuclear fuel is at the basis of a closed nuclear cycle. We don’t think about it too much in the United States because we just don’t reprocess nuclear fuel! Hence, our spent fuel builds up and people wring their hands about the “unsolved problem of nuclear waste”. In other countries, like France and Japan, where spent fuel is reprocessed, things aren’t too much better. Because thanks to the fact that you can’t sustain the “burning” of natural uranium in thermal-spectrum reactors, separated fuel can only get you so far. But they stockpile it waiting for the glorious day of liquid-metal fast breeder reactors that the nuclear industry has been promising for fifty years. (a day I hope will never come!!!)

You just can’t choose a nuclear fuel, or a fuel cycle, without thinking about how to reprocess the fuel. That’s how we got in the mess we’re in in the first place. Fortunately, when the “Oak Ridge boys” were thinking up liquid-fluoride reactors back in the 1950s, reprocessing was a key consideration and they came up with very attractive ways to do it. Their first and fundamental advantage was the fact they were dealing with a fuel already in fluid form. That immediately eliminated all the complicated steps you have to go through with solid fuel: chopping, decladding, dissolution in nitric acid–and that’s just the front end–then reconstitution of the fuel, which usually implies remote fuel fabrication because you’ve still got a lot more radioactivity in the fuel than fresh fuel.

So all those problems were solved from the beginning, just by working with fluid fuel. But you still needed to get through the basic steps of reprocessing, which is, you exploit chemical and physical differences in the materials in the spent fuel to separate out the things you want from the things you don’t want.

I’ve talked previously about the simple steps of fluorination and distillation that liquid-fluoride reprocessing was based on. Fluorination is especially clever–you take advantage of the fact that uranium will absorb more fluorine to go from a tetrafluoride (four fluorine atoms) to a hexafluoride (six fluorine atoms) and in that conversion, will become gaseous. It’s an incredibly nice feature for trying to separate uranium out from just about anything else (assuming all the other stuff won’t do the same trick).

Fluorination works especially well in our core salt of LiF-BeF2-UF4. When you want to get the uranium out, you bubble fluorine gas through the salt. The lithium won’t take any more–it’s perfectly happy with its one fluorine atom. Neither will the beryllium–it’s happy with two. But the uranium says “more fluorine? I’m outta here!” and converts to the gaseous hexafluoride state, leaving you with just LiF-BeF2.

Now after we run an LFTR for awhile, the core salt will contain not only LiF, BeF2, and UF4, but will contain a number of fission product fluorides generated from the fission of U-233. These fission products are responsible for nearly all the radiation levels in the reactor (when it’s shut down) and they are the materials that pose the greatest biological hazard if released. They also can increasingly interfere with continued nuclear operation, because some of them tend to absorb neutrons that would otherwise be going towards fission or conversion of thorium to uranium. So we want then out.

Distillation appears to be the best way to accomplish that. Distillation takes advantage of the fact that the things we want to keep in the salt (the lithium fluoride and beryllium fluorides) tend to vaporize at lower temperatures that the fission product fluorides. Thus by applying heat at reduced pressure, we can get the LiF and BeF2 to separate from the fission product fluorides, leaving them to accumulate in the bottom of the “still”.

Recently I realized that through the proper choice of isotopes, we could accurately test this entire reprocessing system in a completely non-nuclear, nearly non-radioactive manner. If we used U-238 to stand in for the U-233 fuel, and used stable isotopes of the fission products (such as zirconium, strontium, and barium) we could test a chemically-accurate liquid-fluoride reactor. In the blanket salt, we could add small amounts of U-238 to the salt, simulating the generation of U-233 from thorium. Then that U-238 would be removed from the blanket by fluorination. The U-238 would then be added to the core salt, simulating the continuous refueling of the real reactor. Stable fluorides of the fission products would also be added to the core salt, simulating the accumulation of fission products. Both the U-238 and the stable fission product fluorides could be removed by fluorination and distillation.

Two basic advantages of this approach are: 1. because the reprocessing steps chosen for the reactor are not significantly affected by radiation, the lack of radiation does not compromise the accuracy of the test. 2. It will be much easier and cheaper to “wring” out LFR reprocessing techniques on non-radioactive or very low radioactivity materials rather than on real fuel and blanket salt.

I believe that taking this approach to the development of the reprocessing systems for the reactor would speed development and ultimate fielding of the reactor system.

One of my favorite folks, Senator John McCain, is clearly a supporter of nuclear energy. I’m very glad to hear it. One of the (many) drawbacks of today’s uranium-fueled, water-cooled reactors is that they depend on a great deal of cooling water for heat rejection. This limits their use in Western states that have scarce water resources. The three-unit Palo Verde plant in Phoenix uses some careful measures to conserve water.

But by using highly-efficient, closed-cycle helium gas turbines for power conversion, we could envision direct heat rejection to air, which would remove the constraint of needing to locate the plant near large water supplies. This could allow thorium-fueled, liquid-fluoride reactors to be deployed across the West without concern for cooling water supplies. This nice feature, along with the virtual elimination of long-lived transuranic waste should make the thorium LFR a much more popular option with Western congressmen.

Introduction and Basic Principles of Energy Sustainability

The generation and use of energy is central to the maintenance of organization. Life itself is a state of organization maintained by the continual use of sources of energy. Human civilization has reached the state it has by the widespread use of energy, and for the large fraction of the world that aspires to a higher standard of living, more energy will be required for them to achieve it.

Therefore, I embrace the idea that we need energy, and probably need much more of it than we currently have. We should never waste energy, and should always seek to use energy efficiently as possible and practical, but energy itself will always be needed.

This weblog is about the use of thorium as an energy source of sufficient magnitude for thousands of years of future energy needs. Thorium, if used efficiently, can be converted to energy far more easily and safely than any other energy source of comparable magnitude, including nuclear fusion and uranium fission.

Briefly, my basic principles are:

1. Nuclear reactions (changes in the binding energy of nuclei) release about a million times more energy than chemical reactions (changes in the binding energy of electrons), therefore, it is logical to pursue nuclear reactions as dense sources of energy.

2. Changing the binding energy of the nucleus with uncharged particles (neutrons inducing fission) is much easier than changing the nuclear state with charged particles (fusion), because fission does not contend with electrostatic repulsion as fusion does.

3. Naturally occuring fissile material (uranium-235) will not sustain us for millennia due to its scarcity. We must fission fertile isotopes (uranium-238, thorium-232) which are abundant in order to sustain energy production for millenia. Fertile isotopes such as U-238 and Th-232 basically require 2 neutrons to fission (one to convert, one to fission), and require fission reactions that generate more than 2 neutrons per absorption in a fissile nucleus.

4. For maximum safety, nuclear reactions should proceed in a thermal (slowed-down) neutron spectrum because only thermal reactors can be designed to be in their most critical configuration, where any alteration to the reactor configuration (whether through accident or intention) leads to less nuclear reactions, not more. Thermal reactors also afford more options for achieving negative temperature coefficients of reactivity (which are the basic measurement of the safety of a nuclear reactor). Reactors that require neutrons that have not been slowed significantly from their initial energy (fast-spectrum reactors) can always be altered in some fashion, either through accident or intention, into a more critical configuration that could be dangerously uncontrollable because of the increased reactivity of the fuel. Basically, any fast-spectrum reactor that is barely critical will be extremely supercritical if its neutrons are moderated in some way.

5. “Burning” uranium-238 produces a fissile isotope (plutonium-239) that “burns” inefficiently in a thermal (slowed-down) neutron spectrum and does not produce enough neutrons to sustain the consumption of uranium-238. “Burning” thorium-232 produces a fissile isotope (uranium-233) that burns efficiently in a thermal neutron spectrum and produces enough neutrons to sustain the consumption of thorium. Therefore, thorium is a preferable fuel, if used in a neutronically efficient reactor.

6. Achieving high neutronic efficiency in solid-fueled nuclear reactors is difficult because the fuel sustains radiation damage, the fuel retains gaseous xenon (which is a strong neutron poison), and solid fuel is difficult to reprocess because it must be converted to a liquid stream before it is reprocessed.

7. Fluid-fuel reactors can continuously strip xenon and adjust the concentration of fuel and fission products while operating. More importantly, they have an inherently strong negative temperature coefficient of reactivity which leads to inherent safety and vastly simplified control. Furthermore, decay heat from fission products can be passively removed (in case of an accident) by draining the core fluid into a passively cooled configuration.

8. Liquid-fluoride reactors have all the advantages of a fluid-fueled reactor plus they are chemically stable across a large temperature range, are impervious to radiation damage due to the ionic nature of their chemical bond. They can dissolve sufficient amounts of nuclear fuel (thorium, uranium) in the form of tetrafluorides in a neutronically inert carrier salt (lithium7 fluoride-beryllium fluoride). This leads to the capability for high-temperature, low-pressure operation, no fuel damage, and no danger of fuel precipitation and concentration.

9. The liquid-fluoride reactor is very neutronically efficient due to its lack of core internals and neutron absorbers; it does not need “burnable poisons” to control reactivity because reactivity can continuously be added. The reactor can achieve the conversion ratio (1.0) to “burn” thorium, and has superior operational, safety, and development characteristics.

10. Liquid-fluoride reactors can retain actinides while discharging only fission products, which will decay to background levels of radiation in ~300 years and do not require long duration (>10,000 year) geologic burial.

11. A liquid-fluoride reactor operating only on thorium and using a “start charge” of pure U-233 will produce almost no transuranic isotopes. This is because neutron capture in U-233 (which occurs about 10% of the time) will produce U-234, which will further absorb another neutron to produce U-235, which is fissile. U-235 will fission about 85% of the time in a thermal-neutron spectrum, and when it doesn’t it will produce U-236. U-236 will further absorb another neutron to produce Np-237, which will be removed by the fluorination system. But the production rate of Np-237 will be exceedingly low because of all the fission “off-ramps” in its production.

12. We must build thousands of thorium reactors to displace coal, oil, natural gas, and uranium as energy sources. This would be impractical if liquid-fluoride reactors were as difficult to build as pressurized water reactors. But they will be much simpler and smaller for several reasons. They will operate at a higher power density (leading to a smaller core), they will not need refueling shutdowns (eliminating the complicated refueling equipment), they will operate at ambient pressure and have no pressurized water in the core (shrinking the containment vessel dramatically), they will not require the complicated emergency core cooling systems and their backups that solid-core reactors require (because of their passive approach to decay heat removal), and their power conversion system will be much smaller and power-dense (since in a closed-cycle gas turbine you can vary both initial cycle pressure and overall pressure ratio). In short, these plants will be much smaller, much simpler, much, much safer, and more secure.

That said, I am not an apologist for the nuclear industry. I think that a fundamental mistake was made when thorium was overlooked as the prime nuclear fuel in favor of uranium, and this blog is an attempt to explain my position on that topic. In such a position, I think I stand in some good company. Dr. Alvin Weinberg, former director of the Oak Ridge National Laboratory and inventor of the pressurized-water reactor (he holds the patent) said in 1970:

The achievement of a cheap, reliable, and safe breeder remains the primary task of the nuclear energy community. (In expressing this view, I suppose I betray a continuing frustration at the slow progress of fusion research, even though the Russian success with the tokamak has quickened the pace.) Actually not much has changed in this regard in 25 years. Even during World War II, many people realized that the breeder was cent
ral. It is only now, with burner reactors doing so well, that the world generally has mobilized around the great aim of the breeder.

As all readers of Nuclear Applications & Technology know, the prevailing view holds that the LMFBR is the proper path to ubiquitous, permanent energy. It is no secret that I, as well as many of my colleagues at ORNL, have always felt differently. When the idea of the breeder was first suggested in 1943, the rapid and efficient recycle of the partially spent core was regarded as the main problem. Nothing that has happened in the ensuing quarter-century has fundamentally changed this.

The successful breeder will be the one that can deal with the spent core most rationally—either by achieving extremely long burnup, or by greatly simplifying the entire recycle step. We at Oak Ridge have always been intrigued by this latter possibility. It explains our long commitment to liquid-fueled reactors-first, the aqueous homogeneous and now, the molten salt.

The molten-salt system has been worked on, mainly at Oak Ridge, for about 22 years. For the first 10 years, our work was aimed at building a nuclear aircraft power plant. The first molten-salt reactor, the Aircraft Reactor Experiment, was described in a series of papers from Oak Ridge that appeared in the November 1957 issue of Nuclear Science and Engineering.

The present series of papers reports the status of molten-salt systems, and particularly the experience we have had with the Molten-Salt Reactor Experiment (MSRE). The tone of optimism that pervades these papers is hard to suppress. And indeed, the enthusiasm displayed here is no longer confined to Oak Ridge. There are now several groups working vigorously on molten salts outside Oak Ridge. The enthusiasm of these groups is not confined to MSRE, nor even to the molten-salt breeder. For we now realize that molten-salt reactors comprise an entire spectrum of embodiments that parallels the more conventional solid-fueled systems. Thus molten-salt reactors can be converters as well as breeders; and they can be fueled with either 239Pu or 233U or 235U.

However, we are aware that many difficulties remain, especially before the most advanced embodiment, the Molten-Salt Breeder, becomes a reality. Not all of these difficulties are technical. I have faith that with continued enlightened support of the US Atomic Energy Commission, and with the open-minded, sympathetic attention of the nuclear community that these papers should encourage, molten-salt reactors will find an important niche in the unfolding nuclear energy enterprise.

Weinberg’s faith in the AEC was unjustified, for just a few years later they moved to kill the liquid-fluoride reactor in favor of the liquid-metal fast breeder. I think this was (and is) a mistake, for only in the liquid-fluoride reactor can we find the safety, economy, and efficiency needed to unlock the potential of thorium energy for tens of thousands of years.

Introduction and Basic

Principles of Energy

The generation and use of energy is central to the maintenance of organization. Life itself is a state of organization maintained by the continual use of sources of energy. Human civilization has reached the state it has by the widespread use of energy, and for the large fraction of the world that aspires to a higher standard of living, more energy will be required for them to meet it.

Therefore, I embrace the idea that we need energy, and probably need much more of it than we currently have. We should never waste energy, and should always seek to use energy efficiently as possible and practical, but energy itself will always be needed.

This weblog is about the use of thorium as an energy source of sufficient magnitude for thousands of years of future energy needs. Thorium, if used efficiently, can be converted to energy far more easily and safely than any other energy source of comparable magnitude, including nuclear fusion and uranium fission.

Briefly, my basic principles are:

1. Nuclear reactions (changes in the binding energy of nuclei) release about a million times more energy than chemical reactions (changes in the binding energy of electrons), therefore, it is logical to pursue nuclear reactions as dense sources of energy.

2. Changing the binding energy of the nucleus with uncharged particles (neutrons inducing fission) is much easier than changing the nuclear state with charged particles (fusion), because fission does not contend with electrostatic repulsion as fusion does.

3. Naturally occuring fissile material (uranium-235) will not sustain us for millennia due to its scarcity. We must fission fertile isotopes (uranium-238, thorium-232) which are abundant in order to sustain energy production for millenia. Fertile isotopes such as U-238 and Th-232 basically require 2 neutrons to fission (one to convert, one to fission), and require fission reactions that generate more than 2 neutrons per absorption in a fissile nucleus.

4. For maximum safety, nuclear reactions should proceed in a thermal (slowed-down) neutron spectrum because only thermal reactors can be designed to be in their most critical configuration, where any alteration to the reactor configuration (whether through accident or intention) leads to less nuclear reactions, not more. Thermal reactors also afford more options for achieving negative temperature coefficients of reactivity (which are the basic measurement of the safety of a nuclear reactor). Reactors that require neutrons that have not been slowed significantly from their initial energy (fast-spectrum reactors) can always be altered in some fashion, either through accident or intention, into a more critical configuration that could be dangerously uncontrollable because of the increased reactivity of the fuel. Basically, any fast-spectrum reactor that is barely critical will be extremely supercritical if its neutrons are moderated in some way.

5. “Burning” uranium-238 produces a fissile isotope (plutonium-239) that “burns” inefficiently in a thermal (slowed-down) neutron spectrum and does not produce enough neutrons to sustain the consumption of uranium-238. “Burning” thorium-232 produces a fissile isotope (uranium-233) that burns efficiently in a thermal neutron spectrum and produces enough neutrons to sustain the consumption of thorium. Therefore, thorium is a preferable fuel, if used in a neutronically efficient reactor.

6. Achieving high neutronic efficiency in solid-fueled nuclear reactors is difficult because the fuel sustains radiation damage, the fuel retains gaseous xenon (which is a strong neutron poison), and solid fuel is difficult to reprocess because it must be converted to a liquid stream before it is reprocessed.

7. Fluid-fuel reactors can continuously strip xenon and adjust the concentration of fuel and fission products while operating. More importantly, they have an inherently strong negative temperature coefficient of reactivity which leads to inherent safety and vastly simplified control. Furthermore, decay heat from fission products can be passively removed (in case of an accident) by draining the core fluid into a passively cooled configuration.

8. Liquid-fluoride reactors have all the advantages of a fluid-fueled reactor plus they are chemically stable across a large temperature range, are impervious to radiation damage due to the ionic nature of their chemical bond. They can dissolve sufficient amounts of nuclear fuel (thorium, uranium) in the form of tetra fluorides in a neutronically inert carrier salt (lithium-7 fluoride-beryllium fluoride). This leads to the capability for high-temperature, low-pressure operation, no fuel damage, and no danger of fuel precipitation and concentration.

9. The liquid-fluoride reactor is very neutronically efficient due to its lack of core internals and neutron absorbers; it does not need “burnable poisons” to control reactivity because reactivity can continuously be added. The reactor can achieve the conversion ratio (1.0) to “burn” thorium, and has superior operational, safety, and development characteristics.

10. Liquid-fluoride reactors can retain actinides while discharging only fission products, which will decay to background levels of radiation in ~300 years and do not require long duration (>10,000 year) geologic burial.

11. A liquid-fluoride reactor operating only on thorium and using a “start charge” of pure U-233 will produce almost no transuranic isotopes. This is because neutron capture in U-233 (which occurs about 10% of the time) will produce U-234, which will further absorb another neutron to produce U-235, which is fissile. U-235 will fission about 85% of the time in a thermal-neutron spectrum, and when it doesn’t it will produce U-236. U-236 will further absorb another neutron to produce Np-237, which will be removed by the fluorination system. But the production rate of Np-237 will be exceedingly low because of all the fission “off-ramps” in its production.

12. We must build thousands of thorium reactors to displace coal, oil, natural gas, and uranium as energy sources. This would be impractical if liquid-fluoride reactors were as difficult to build as pressurized water reactors. But they will be much simpler and smaller for several reasons. They will operate at a higher power density (leading to a smaller core), they will not need refueling shutdowns (eliminating the complicated refueling equipment), they will operate at ambient pressure and have no pressurized water in the core (shrinking the containment vessel dramatically), they will not require the complicated emergency core cooling systems and their backups that solid-core reactors require (because of their passive approach to decay heat removal), and their power conversion system will be much smaller and power-dense (since in a closed-cycle gas turbine you can vary both initial cycle pressure and overall pressure ratio). In short, these plants will be much smaller, much simpler, much, much safer, and more secure.

The Nuclear Industry

That said, I am not an apologist for the nuclear industry. I think that a fundamental mistake was made when thorium was overlooked as the prime nuclear fuel in favor of uranium, and this blog is an attempt to explain my position on that topic. In such a position, I think I stand in some good company.

Dr. Alvin Weinberg, former director of the Oak Ridge National Laboratory and inventor of the pressurized-water reactor (he holds the patent) said in 1970:

The achievement of a cheap, reliable, and safe breeder remains the primary task of the nuclear energy community. (In expressing this view, I suppose I betray a continuing frustration at the slow progress of fusion research, even though the Russian success with the tokamak has quickened the pace.) Actually not much has changed in this regard in 25 years. Even during World War II, many people realized that the breeder was cent
ral. It is only now, with burner reactors doing so well, that the world generally has mobilized around the great aim of the breeder.

As all readers of Nuclear Applications & Technology know, the prevailing view holds that the LMFBR is the proper path to ubiquitous, permanent energy. It is no secret that I, as well as many of my colleagues at ORNL, have always felt differently. When the idea of the breeder was first suggested in 1943, the rapid and efficient recycle of the partially spent core was regarded as the main problem. Nothing that has happened in the ensuing quarter-century has fundamentally changed this.

The successful breeder will be the one that can deal with the spent core most rationally—either by achieving extremely long burnup, or by greatly simplifying the entire recycle step. We at Oak Ridge have always been intrigued by this latter possibility. It explains our long commitment to liquid-fueled reactors-first, the aqueous homogeneous and now, the molten salt.

The molten-salt system has been worked on, mainly at Oak Ridge, for about 22 years. For the first 10 years, our work was aimed at building a nuclear aircraft power plant. The first molten-salt reactor, the Aircraft Reactor Experiment, was described in a series of papers from Oak Ridge that appeared in the November 1957 issue of Nuclear Science and Engineering.

The present series of papers reports the status of molten-salt systems, and particularly the experience we have had with the Molten-Salt Reactor Experiment (MSRE). The tone of optimism that pervades these papers is hard to suppress. And indeed, the enthusiasm displayed here is no longer confined to Oak Ridge. There are now several groups working vigorously on molten salts outside Oak Ridge. The enthusiasm of these groups is not confined to MSRE, nor even to the molten-salt breeder. For we now realize that molten-salt reactors comprise an entire spectrum of embodiments that parallels the more conventional solid-fueled systems. Thus molten-salt reactors can be converters as well as breeders; and they can be fueled with either 239Pu or 233U or 235U.

However, we are aware that many difficulties remain, especially before the most advanced embodiment, the Molten-Salt Breeder, becomes a reality. Not all of these difficulties are technical. I have faith that with continued enlightened support of the US Atomic Energy Commission, and with the open-minded, sympathetic attention of the nuclear community that these papers should encourage, molten-salt reactors will find an important niche in the unfolding nuclear energy enterprise.

Weinberg’s faith in the AEC was unjustified, for just a few years later they moved to kill the liquid-fluoride reactor in favor of the liquid-metal fast breeder. I think this was (and is) a mistake, for only in the liquid-fluoride reactor can we find the safety, economy, and efficiency needed to unlock the potential of thorium energy for tens of thousands of years.

Perhaps the single most important safety aspect of a nuclear reactor is the temperature coefficient of reactivity. This value describes how the reactor will react to an increase or a decrease in reactor temperature. If the coefficient is positive, then an increase in core temperature will cause an increase in reactivity, which will lead the reactor to generate more power, which will increase power more, and so forth until the reactor is destroyed. If the reactor has a negative temperature coefficient, on the other hand, an increase in power will lead to a reduction in core reactivity, which will generate less power, and core temperatures will decrease. All reactors licensed in the United States must demonstrate that they have negative temperature coefficients under all operating conditions. The Chernobyl nuclear reactor accident in 1986 was caused by operators allowing the reactor to enter an operational regime where the reactor had a positive temperature coefficient.

A negative temperature coefficient of reactivity can be thought of with a mechanical analogy. Imagine a mass on the end of a spring attached to a wall. If the mass is subjected to a force, its acceleration, velocity, and ultimate location will be determined by the stiffness (spring constant) of the spring to which it is attached. The stiffness of the spring represents the negative temperature coefficient of reactivity; the force pulling on the spring represents the power demand on the reactor. If there is no power demand on a critical reactor with a negative temperature coefficient, it will produce essentially no power. Upon the addition of a power demand, the reactor responds by increasing its power, until it is producing the power demanded.

If the negative temperature coefficient is infinitely large (corresponding to an infinitely stiff spring) then the reactor will quickly reach its power demand level with no oscillation or overshoot in power. Similarly, if the demand for power is lost, through interruption or accident, then the reactor power will quickly move back to zero with no oscillation.

In a real reactor, with a finite negative temperature coefficient, the response of the reactor to the addition and removal of power demand is more like the response of the mass and the spring. If load is added, then the reactor power goes up but overshoots the demand and has to come back, with damped oscillations that eventually stop and power equals demand. If load is removed, the reactor “bounces” back to the zero power level at a rate that depends on the temperature coefficient. The more negative the temperature coefficient, the more precisely the reactor assumes the desired power level and the less “hunting” for that location takes place.

In typical terrestrial reactors with moderately negative temperature coefficients, there is enough “overshoot” and “bounce” in the reactor’s response that a reactor operator uses control rods to “ride” the oscillations and prevent the reactor from damaging itself during these transients. A properly-designed liquid-fluoride reactor has a very high negative temperature coefficient, since as the reactor temperature increases, the fluoride salt expands in volume, and there is less fissile material in the core to sustain the reaction. Hence, the liquid-fluoride reactor can respond very quickly and accurately to the addition and removal of power load without concern about damage to the reactor during transients.

This is a prime consideration during operation of a space nuclear power system since the primary load will probably be the electric thrusters that provide propulsion. As was shown during the Deep Space 1 mission, electric thrusters (especially ion engines) can short out very quickly and the load on the power system can be lost nearly instantaneously. Some of the space reactor systems being investigated have positive temperature coefficients of reactivity and rely on fast acting control systems and control rod motors to keep the reactor within operational limits. While such systems can be made to work, they must be extraordinarily reliable and have extensive redundancy since the integrity of the reactor depends on them. Even a reactor with a moderately negative temperature coefficient must employ control systems to prevent damage during transients.

A liquid-fluoride reactor, with its large negative temperature coefficient, would be inherently stable and not need to rely on mechanical systems for control. Thus the fast-acting control systems, monitors, redundancy, and extensive testing under all conceivable scenarios will not be necessary for such a reactor. It will reliably and swiftly assume the power level desired and quickly shut down if the power load is lost. Such inherent safety is vastly more desirable than the engineered safety of control systems, and it will lead to lower costs in development, testing, and operations.

This capability is not theoretical–it was actually demonstrated during the operation of both of the liquid-fluoride reactors constructed. Here is an excerpt from a paper describing the operation of the Molten-Salt Reactor Experiment in 1968:

“The dynamic behavior of the MSRE was extensively examined, by theoretical techniques before the reactor was operated and by experiments during the operation. Calculations had indicated that the reactor would be inherently stable at all power levels and that the degree of stability would increase with increasing power, and experimental measurements of the reactor dynamic response agreed very closely with the predictions. In addition, measurements made throughout the operation with U-235 fuel showed that there was no change in dynamic behavior with time.

“Similar theoretical and experimental evaluations were made of the dynamic behavior with U-233 fuel. The calculations indicated that, despite the lower delayed-neutron fraction, the reactor stability would be greater with U-233–due primarily to the larger negative temperature coefficient of reactivity of the fuel salt. Experimental measurements of system transfer functions and transient response are in good agreement with predictions.

“Because of the good self-regulating characteristics of the MSRE, the system is quite simple to control. In more than 15,000 hours of critical operation, not once have the nuclear power, period, or fuel temperature gone out of limits so as to cause a control-rod scram.”

The Safety and Stability Advantages

of a

(LFTR)

Liquid Fluoride Thorium Reactor

in the Space Environment

Perhaps the single most important safety aspect of a nuclear reactor is the temperature coefficient of reactivity. This value describes how the reactor will react to an increase or a decrease in reactor temperature. If the coefficient is positive, then an increase in core temperature will cause an increase in reactivity, which will lead the reactor to generate more power, which will increase power more, and so forth until the reactor is destroyed. If the reactor has a negative temperature coefficient, on the other hand, an increase in power will lead to a reduction in core reactivity, which will generate less power, and core temperatures will decrease. All reactors licensed in the United States must demonstrate that they have negative temperature coefficients under all operating conditions. The Chernobyl nuclear reactor accident in 1986 was caused by operators allowing the reactor to enter an operational regime where the reactor had a positive temperature coefficient.

Negative Temperature Coefficient

A negative temperature coefficient of reactivity can be thought of with a mechanical analogy. Imagine a mass on the end of a spring attached to a wall. If the mass is subjected to a force, its acceleration, velocity, and ultimate location will be determined by the stiffness (spring constant) of the spring to which it is attached. The stiffness of the spring represents the negative temperature coefficient of reactivity; the force pulling on the spring represents the power demand on the reactor. If there is no power demand on a critical reactor with a negative temperature coefficient, it will produce essentially no power. Upon the addition of a power demand, the reactor responds by increasing its power, until it is producing the power demanded.

If the negative temperature coefficient is infinitely large (corresponding to an infinitely stiff spring) then the reactor will quickly reach its power demand level with no oscillation or overshoot in power. Similarly, if the demand for power is lost, through interruption or accident, then the reactor power will quickly move back to zero with no oscillation.

Real World Factors

In a real reactor, with a finite negative temperature coefficient, the response of the reactor to the addition and removal of power demand is more like the response of the mass and the spring. If load is added, then the reactor power goes up but overshoots the demand and has to come back, with damped oscillations that eventually stop and power equals demand. If load is removed, the reactor “bounces” back to the zero power level at a rate that depends on the temperature coefficient. The more negative the temperature coefficient, the more precisely the reactor assumes the desired power level and the less “hunting” for that location takes place.

In typical terrestrial reactors with moderately negative temperature coefficients, there is enough “overshoot” and “bounce” in the reactor’s response that a reactor operator uses control rods to “ride” the oscillations and prevent the reactor from damaging itself during these transients. A properly-designed liquid-fluoride reactor has a very high negative temperature coefficient, since as the reactor temperature increases, the fluoride salt expands in volume, and there is less fissile material in the core to sustain the reaction. Hence, the liquid-fluoride reactor can respond very quickly and accurately to the addition and removal of power load without concern about damage to the reactor during transients.

Extraterrestrial Considerations

This is a prime consideration during operation of a space nuclear power system since the primary load will probably be the electric thrusters that provide propulsion. As was shown during the Deep Space 1 mission, electric thrusters (especially ion engines) can short out very quickly and the load on the power system can be lost nearly instantaneously. Some of the space reactor systems being investigated have positive temperature coefficients of reactivity and rely on fast acting control systems and control rod motors to keep the reactor within operational limits. While such systems can be made to work, they must be extraordinarily reliable and have extensive redundancy since the integrity of the reactor depends on them. Even a reactor with a moderately negative temperature coefficient must employ control systems to prevent damage during transients.

LFTR  Stability

A LFTR Liquid Fluoride Thorium Reactor, with its large negative temperature coefficient, would be inherently stable and not need to rely on mechanical systems for control. Thus the fast-acting control systems, monitors, redundancy, and extensive testing under all conceivable scenarios will not be necessary for such a reactor. It will reliably and swiftly assume the power level desired and quickly shut down if the power load is lost. Such inherent safety is vastly more desirable than the engineered safety of control systems, and it will lead to lower costs in development, testing, and operations.

This capability is not theoretical–it was actually demonstrated during the operation of both of the liquid-fluoride reactors constructed. Here is an excerpt from a paper describing the operation of the Molten-Salt Reactor Experiment in 1968:

“The dynamic behavior of the MSRE was extensively examined, by theoretical techniques before the reactor was operated and by experiments during the operation. Calculations had indicated that the reactor would be inherently stable at all power levels and that the degree of stability would increase with increasing power, and experimental measurements of the reactor dynamic response agreed very closely with the predictions. In addition, measurements made throughout the operation with U-235 fuel showed that there was no change in dynamic behavior with time.

“Similar theoretical and experimental evaluations were made of the dynamic behavior with U-233 fuel. The calculations indicated that, despite the lower delayed-neutron fraction, the reactor stability would be greater with U-233–due primarily to the larger negative temperature coefficient of reactivity of the fuel salt. Experimental measurements of system transfer functions and transient response are in good agreement with predictions.

“Because of the good self-regulating characteristics of the MSRE, the system is quite simple to control. In more than 15,000 hours of critical operation, not once have the nuclear power, period, or fuel temperature gone out of limits so as to cause a control-rod scram.”

On Thursday, the LDS Church announced its opposition to a planned temporary nuclear waste storage facility in the west desert of Utah. Furthermore, they called on “the federal government to harness the technological and creative power of the country to develop options for the disposal of nuclear waste.”

This is significant because due to delays in the opening of Yucca Mountain, utilities had contracted with the Goshute Indian tribe of Utah to site high-level nuclear waste (spent fuel rods) on Goshute land (in Skull Valley). The utilities saw it as an opportunity to get their spent fuel away from their reactors and a lot closer to Yucca. The Goshutes saw it as a way to make a few billion dollars. The federal government saw it as encroachment on Yucca and potentially a move by the utilities to get all the billions they paid into the waste disposal fund returned. And Nevada saw it as an opportunity to add Utah to the “no waste in my state” crowd.

Now with the LDS Church weighing in on the matter, the Skull Valley deal is probably dead. This will put greater pressure on the government to open Yucca, which will probably intensify opposition from the Nevadans.

I bring all this up because a fast-spectrum, liquid-chloride reactor would be ideal for destroying this high-level waste and rendering it into a form that must only be isolated for a few hundred years. When the isolation time goes from 10,000 years to a few hundred years, potential disposal sites increase exponentially. Heck, you could probably store it all in one place for that long.

The liquid-chloride reactor option was most thoroughly explored by Dr. Mieczyslaw Taube of Poland, and later work was done by his student Dr. Eric Ottewitte, who later championed the LCFR to the Idaho National Lab. Here is a collection of some of their papers on the subject. Perhaps someone ought to send them to the LDS Church.