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.