EnergyFromThorium

“But the gift of God is eternal life through Jesus Christ our Lord…”

–Romans 6:23

Keith Schwartztrauber, a self-declared “old nuke”, wrote a letter in the November/December 2010 issue of American Scientist , which had published Liquid Fuel Nuclear Reactors by Robert Hargraves and Ralph Moir.

To the Editors:

Robert Hargraves and Ralph Moir’s article “Liquid Fluoride Thorium Reactors” (July–August) was a pleasure to read but stirred concern in me. I have studied many reactor concepts dating to the 1960s. The authors correctly note advantages to the thorium fuel cycle. Given the commercial failures of the thorium-based high-temperature gas-cooled reactor (HTGR) and the demise of the thorium-based Shippingport light-water breeder reactor (LWBR), however, I don’t envision the liquid fluoride thorium reactor concept playing a central role. The developmental, technical, safety, regulatory and financial challenges are probably insurmountable.

U.S. nuclear reactors are constructed with solid fuel, metal cladding, water coolant, high integrity pressure vessels and piping, and concrete and steel pressure containments. For sound reasons, the Nuclear Regulatory Commission required their designers to assume that the system’s largest pipe could instantly rupture and release reactor coolant to the containment. It was assumed that large fractions of the reactor core fission products and any hydrogen generated would be released. In the case of the HTGR, this included potential graphite-water reactions (yielding hydrogen) and graphite-air reactions (yielding fire) in the core.

With the liquid fluoride thorium reactors (LFTRs), a total loss of coolant is equivalent to a total loss of the liquid core, fuel and blanket materials to the containment. Since the liquid fluoride operates at temperatures of 800 degrees Celsius, it is quite likely that UF4, ThF4 and fission by-products would react with other materials to cause a criticality event, major fires and/or explosions. I find it hard to believe that anyone would endorse building new reactors using such a chemically complex, potentially unsafe, environmentally hazardous, and unproven technology.

Keith Schwartztrauber
Las Vegas, NV

Underground molten salt reactor by Moir and Teller

 Drs. Hargraves and Moir respond:

A criticality event would not occur during a total rupture of the reactor vessels because the materials would leave the compact geometry that permits criticality. Also the neutron fission cross sections will reduce as the materials leave the reactor and moderator, thereby hardening the neutron spectra. By design, the reactor room is steel-lined with strongly sloping floors leading to drains. Spilled molten salt would flow to holding tanks designed to treat such an event as “normal” rather than a big “accident.” The continuous chemical processing removes most fission products, especially the gaseous ones that would build up a pressure as they are created, reducing that hazard. The amount of fissile material within an LFTR is a fraction of that within today’s water-cooled power reactors or proposed liquid-metal-cooled fast breeder reactors. The LFTR needs only a low-pressure containment structure, perhaps below ground.

Many of the LFTR chemical processes were pioneered at Oak Ridge and Argonne national laboratories and are used in the aluminum and uranium fuel manufacturing industries, but not within today’s U.S. power reactors. Acceptance of LFTR, “the chemist’s reactor,” will require new skills within the NRC, the nuclear industry and the utilities. These LFTR safety features require validation that can only be achieved by a concerted research and development effort—estimated to cost less than a billion dollars excluding new reactor construction—to bring the technology to a level exceeding that already demonstrated at Oak Ridge.

I was very fortunate to meet Dr. Kazuo Furukawa in person several weeks ago, and he shared with me a fascinating talk that had somehow escaped my attempts to discover everything Alvin Weinberg said or thought or wrote down about the molten-salt reactor.

The talk was called “The proto-history of the molten salt system” and it was given by Weinberg on February 23, 1997 to a delegation of Korean scientists visiting Oak Ridge National Lab.

Weinberg’s biography “The First Nuclear Era” doesn’t say nearly as much about his experiences with MSR technology as I would have hoped, but it still says the vast majority of what we know about what he thought. I have extracted a number of key quotes from the text and kept them in a PPT file for some time.

This talk is full of fascinating insights, some of which I have wondered about for years. For instance, who REALLY invented the idea of a nuclear reactor running on liquid fluoride salt? I was pretty sure that it wasn’t exactly Ray Briant, although he led the effort. I had wondered, from what I had read, if some of the K-25 personnel had conceived the idea first.

No.

It was none other than Eugene Wigner himself:

There were two people at the metallurgical laboratory, Harold Urey, the isotope chemist, and Eugene Wigner, the designer of Hanford, both Nobel Prize winners who always argued that we ought to investigate whether chain reactors, engineering devices that produced energy from the chain reaction, ought to be basically mechanical engineering devices or chemical engineering devices. And Wigner and Urey insisted that we ought to be looking at chemical devices—that means devices in which the fuel elements were replaced by liquids. Even in the earliest days people began thinking what kind of liquid would you have in a chain reactor. One of the liquids that was first looked at was slurry of uranium oxide in heavy water, but Wigner was not satisfied with that, and he had one of his people look into whether molten fluorides would be a possibility. So the ideas of molten fluorides first came into the chain reaction community by 1945.

What did the Atomic Energy Commission think of thorium and MSR technology?

In 1962 when there was a big report put out by the Atomic Energy Commission about the future of nuclear energy; it was generally believed you that you would have burner reactors such as we have now or low conversion-ratio converters, and that these would then be gradually replaced by breeder reactors. But at that time we were very careful especially here at the Oak Ridge National Laboratory not to say fast breeder. The word was breeder reactors, not necessarily fast breeders. But Oak Ridge in a way was alone in insisting that thermal breeders, as well as fast breeders, ought to be considered. And there was indeed at that time a tendency within the Atomic Energy Commission to divide the breeder business into the plutonium breeder, which was generally viewed as a fast breeder, and the thorium breeder, and Oak Ridge elected to be the thorium breeder laboratory, because of our history and because the Molten-Salt Reactor lent itself so well to thorium breeding. Now this turned out in retrospect to be, I suppose you say, a political mistake, because the people in Washington were very much influenced by the bulk of the opinion which held that breeder meant fast breeder. Breeder meant sodium cooling. Breeder meant heterogeneous solid fuel element, and for the upstarts in the little town of Oak Ridge, Tennessee, to claim, now wait a minute, there’s another way to go, and this is based on thorium, is based on liquid fuel, that was too far out of the mainstream, and so the thorium breeder, although it was mentioned quite prominently in this 1962 report by the Atomic Energy Commission the thorium breeder never received the political support and the organizational support within the Atomic Energy Commission that the fast breeder received. And therefore, the thorium breeder always has been, until I suppose rather recently, a second-class citizen. What is going to happen now, I don’t know.

And more insight into the quintessential question–why didn’t this happen?

Because the technology was too different from what they were doing then.

I often have asked myself now why was it t his beautiful idea we really had, these wonderful things about these fluid fuels and so on, why is it that the powers that be in the Atomic Energy Commission never quite took the matter fully seriously. And I think the answer is, that the technology of fluid fuel is so different from the technology of solid fuel, the whole question of the maintainability of the system is so many orders of magnitude different than the problem of maintainability of the solid systems, that the people who were prepared to spend hundreds of millions of dollars on fast reactors just couldn’t make that jump. And that basically was the reason why the system did not prosper the way it should have, although in those early discussions there were considerable arguments about which reactor was safer – the fast breeder reactor, heterogeneous, plutonium, the molten salt breeder. And generally speaking, and this was a view that was supported by one of the very important commissioners, Tommy Thompson, (who died in an airplane crash, he was kind of a safety expert for the Atomic Energy Commission), always insisted that the Thorium Molten Salt Reactor was fundamentally safer, than the LMFBR (Liquid Metal Fast Breeder Reactor).

Read the whole thing. It’s in the document repository now.

In response to the Liquid Fuel Nuclear Reactor article by Robert Hargraves and Ralph Moir, the September/October 2010 issue of American Scientist printed an exchange of letters initiated by Cameron Reed of Alma College.

U-233 is created in the Th-232 blanket

To the Editors:

Robert Hargraves and Ralph Moirs article Liquid Fluoride Thorium Reactors (July August 2010) presents a strong case for developing such plants. The relative simplicity of their construction and operation, their inherent safety and their lack of plutonium production are powerful advantages that should be carefully considered. However, their nonproliferation potential may not be quite as promising as they imply.

The authors, just as Mujid Kazimi did previously (see, Thorium Fuel for Nuclear Energy, American Scientist, Sept.Oct. 2003), suggest that U-232 in the U-233 produced by thorium reactors makes proliferation unlikely, due to the formers prolific and high-energy gamma-ray emissions. Neither article quantified how much U-232 is produced, making the claim difficult to judge. The first reaction in the production of U-232 has an extremely small cross-section for neutrons below about 6 mega-electron volts. As only a small fraction of neutrons generated in fissions are this energetic, the production rate of U-232 is very low.

U-233 is an excellent fuel for a fission weapon. It has a considerably smaller bare critical mass than U-235, about 15 kilograms versus 45 kilograms. This can be made significantly smaller perhaps halved by use of a lightweight beryllium tamper. Unlike the plutonium present in spent fuel, U-233 is immune to predetonation problems in even a crude gun-type bomb due to its low rate of spontaneous fission. It is a fairly copious alpha decayer, a property that can lead to premature detonation if the core is contaminated by light elements. But because the rate of alpha decay is only about one-sixth of that of Pu-239, this might not represent an insurmountable purification problem for would-be bombmakers. Perhaps liquid-fluoride thorium reactors could be engineered to enhance production of U-232 as a nonproliferation measure even if that produced a performance penalty.

Cameron Reed
Alma College

U-232 is produced in the fuel core

Drs. Hargraves and Moir respond:

A commercial reactor will make just enough uranium to sustain power generation. Diverting any would stop the reactor, alerting authorities to a breach. Certainly terrorists could not steal uranium-233 dissolved in a molten salt solution along with lethally radioactive fission products inside a sealed reactor. International Atomic Energy Agency (IAEA) safeguards would require security, accounting of all nuclear materials, surveillance and intrusive inspections. It is conceivable that a nation or revolutionary group might expel IAEA observers, stop a LFTR and attempt to remove U-233. Skilled engineers would need to modify the radioactive reactor’s fluorination equipment to separate uranium from the fuel salt. U-233 produced in a liquid-fluoride thorium reactor (LFTR) is a poor choice for nuclear weapons because the neutrons that produce U-233 also produces 0.13 percent contaminating U-232, whose decay products emit 2.6 mega-electron volt, penetrating gamma radiation. That would be hazardous to weapons builders and obvious to detection monitors. The U-232 decays via a cascade of elements to thallium, which emits the radiation. A year after U-233 separation, a weapons worker one meter from a subcritical 5-kilogram sphere would receive a radiation dose of 4,200 millirems per hour, compared to 0.3 millirems per hour from plutonium. Death becomes probable after 72 hours of exposure. After 10 years, this radiation triples. U-232 cannot be removed chemically. Centrifuge separation would make the equipment too radioactive to maintain. Conceivably, nuclear experts might try to devise chemistry to remove the intermediate elements of the U-232 decay chain before thallium is formed. But at-risk nations could be limited to using a LFTR variant with no chemical processing capability.

Deploying LFTRs will decrease, not increase risks of nuclear weapons proliferation. Kick-starting LFTRs with plutonium can consume existing stocks of that weapons-capable material. Using thorium fuel reduces the need for U-235 enrichment plants, which can make weapons material as well as power reactor fuel. This energy source is cheaper than coal, can increase prosperity and can reduce the potential for wars over resource competition.

US advanced nuclear fission R&D is starving

The US DOE invested $16 billion into R&D for the liquid sodium cooled fast breeder reactor. The work carried out by Argonne National Labs on this Integral Fast Reactor was cancelled during the Clinton administration, under the guise that IFR would increase nuclear weapons proliferation. That was the wrong reason. A good reason is that LFTR is a better technology.

The graph comes from a presentation by Von Hipple, who got the data from the IAEA, which obtained it from DOE. The data are adjusted to $2011 to compare to the DOE 2011 budget items.

$103 million is the largest budget item for advanced nuclear power, funding the prolonged Next Generation Nuclear Plant (NGNP) project. It is a high temperature gas reactor with TRISO fuel form (triple barrier fuel grains) in either pebbles or hexagonal compacts. The choice will be made as soon as the competition between Westinghouse (pebble bed) or General Atomics ends. One advantage of NGNP over LWRs is the high temperature for applications such as dissociating hydrogen from water and achieving higher burnup leading to less waste. Can NGNP scale up to meet the goals of Aim High?

There is still a $22 million budget item that is principally for continuing research in fast reactors, such as IFR.

Although there is $40 million allocated to Advanced Fuel Cycles, there is none for closed fuel cycles! And none for liquid fuels.

One more thing to note is that there is no budget item at all for GNEP, the Global Nuclear Energy Program. GNEP was a multinational program to guarantee fuel supplies to all nations, without the possibility of cutting off fuel as a sanction for bad behavior. This would discourage nations from building uranium enrichment facilities. [In the last few months Jordan, Vietnam, and South Korea have joined the list of countries planning to build centrifuge uranium enrichment plants.] GNEP also provided for the return of the spent fuel to the supplier nations, so as not to provide a reason to build fuel reprocessing facilities. [The US just OK'd India's plans to reprocess US-sourced fuel, since we can't take it back. South Korea says it will reprocess spent fuel because they have no more room for the waste.] The DOE GNEP budget was zeroed at the beginning of the current administration, and all mentions of GNEP were removed from the DOE web site.

Are we spending enough on R&D for advanced nuclear power, such as LFTR?

After two days of meetings for the Fuel Cycle Subcommittee of the Blue Ribbon Commission on America’s Nuclear Future, the public had an opportunity to make statements before the commission. These public statements were meant to be less that five minutes and were allotted on a first come, first serve basis. So bright and early this morning, my friend Rod Adams and I were at the committee table signing up for our spot. I went first and delivered the following statement:

Commissioners, it is my pleasure to participate in this meeting and to address you today. Yesterday there were a number of discussions on the nuclear fuel cycle. These seemed to focus on whether or not fuel recycle should take place, and if it does, whether it should proceed in a thermal-spectrum reactor like our light-water reactors, or if it should proceed in a fast-spectrum reactor, of which the most commonly discussed type is based on solid fuel cooled by liquid sodium.

Another way to view these two options is that one represents the consumption of uranium-235, which is our only naturally-occurring fissile material, and the other represents the consumption of uranium-238 and its derivatives, primarily plutonium-239. Due to the specific properties of uranium-238, it can only be consumed in a sustainable manner in a fast-spectrum reactor.

There is another option that receives relatively little attention but has compelling attributes, and that is the use of natural thorium in nuclear reactors. Thorium is fertile and can be converted into a fissile nuclide, uranium-233, inside a reactor core. Uranium-233 has the compelling attribute of being able to produce enough neutrons in thermal-spectrum fission to continue the conversion of thorium to U-233 and then into energy.

Early in the nuclear age it was realized that this special property had superlative value. Early luminaries like Eugene Wigner and Alvin Weinberg worked to develop nuclear reactors based on liquid fuels. Research focused on a fluoride salt fuel form because it was the only appropriate liquid into which thorium could be dissolved as a true solution. Weinberg’s research and development program at Oak Ridge in the 1960s showed that it was possible to build and safely operate liquid-fluoride thorium reactors.

The fluoride fuel form is particularly compelling since it represents the most chemically stable form of nuclear fuel. In fact, all of our nuclear fuel goes through a fluoride form in today’s nuclear fuel cycle, preparatory to enrichment. We know how to turn uranium oxide into uranium fluoride and we do it every day at conversion plants. Then we successfully use uranium fluoride in enrichment plants. Many of these technological accomplishments are directly applicable to the use of thorium and uranium fluorides in fluid-fueled reactors.

Thorium’s performance means that it is possible to build a reactor that, once started on fissile material, requires no additional fissile input and runs only on thorium. This has profound consequences for our energy future.

Fluoride reactor technologies can also be used to help solve our current nuclear waste concerns. Our spent uranium-oxide could be fluorinated into a fluoride fuel form. Once converted, it is straightforward to remove the uranium that comprises roughly 95% of spent nuclear fuel into uranium hexafluoride gas that could be removed and potentially recycled.

The same nuclear technology that allows us to use thorium could also be used to destroy plutonium while extracting electrical energy. Fluoride fuels will not require the long and lengthy fuel qualification programs that solid fuel require. Fluoride fuels are impervious to radiation damage due to their ionic chemical bonds. They do not swell, crack, or undergo other property changes under strong irradiation. The base fluoride can be used and reused essentially forever, by adding fuel and removing fission products periodically.

I encourage the commission to strongly consider the potential benefits of using fluid-fueled reactor technology to solve our current nuclear waste concerns as well as to open a bright new energy future based on the effective use of natural thorium.

Thank you.

After I spoke, Rod Adams spoke about the importance of nuclear energy in realizing low-cost energy. Another gentlemen spoke about the importance of getting certified as a professional engineer (something I plan to do within the next few years). And John Kutsch of the Thorium Energy Alliance delivered another strong message encouraging the commission to consider the promise of thorium and LFTR.

By the time we had a chance to speak, the audience had dwindled considerably, from about 30 for the afternoon session to perhaps only 20 or so by the time we spoke. But a number of key people were in the audience, like Dr. Eric Loewen, the president of the American Nuclear Society. Of the original subcommittee members, only Per Peterson and Allison MacFarlane remained.

Previous to my statement I delivered a printed package of several “introductory” slides to the members of the commission. You can download them if you want.

There is an upcoming meeting of the Reactor and Fuel Cycle Subcommittee of the Blue Ribbon Commission on America’s Nuclear Future. It will be held in Washington DC at the Washington Marriott on Monday and Tuesday, August 30 and 31, from 8am to 4:15pm.

Announcement

This is the place to make our voices heard about LFTR and the potential of thorium to meet our future energy needs!

Please consider attending the meeting and making your comments heard at the public session on the afternoon of the 31st. There will be one hour for comments.

I am planning to go and comment.  I hope I am joined by many others!

When economic well-being measured by the gross domestic product exceeds a threshold, birthrate drops sharply.

Global warming now threatens irreversible climate damage, ending glacial water flows needed to sustain food production for hundreds of millions of people, and shrinking the polar cold water regions of the ocean where algae start the ocean food chain. Atmospheric CO2 dissolving into the ocean acidifies it, killing corals and stressing ocean life. Demand for biofuels increases destruction of CO2 absorbing forests and jungles.

Burning coal for power is the largest source of atmospheric CO2, which drives global warming. Airborne coal soot causes 24,000 annual deaths in the US and 400,000 in China. We seek alternatives such as burying CO2, or substituting wind, solar, and nuclear power.

The world population growing from 6.7 to 9 billion will increase resource competition, exacerbating environment stress. Yet the OECD nations, with adequate energy supplies, have birthrates lower than needed for population replacement. Nations with GDP per capita over $7,500 have sustainable birthrates. Electricity for water, sanitation, lighting, cooking, refrigeration, communications, health care, and industry contributes to economic development. Those nations with per capita electricity of 2,000 kWh/year (1/6 US use and an average power of 230 W) do achieve GDP of $7,500 per capita, which leads to sustainable birthrates.

Taxing carbon seeks to encourage energy sources that do not emit CO2, yet this has not been effective in Europe. Developing countries will not agree to carbon taxes and forgo an advantage they perceive led to prosperity in OECD nations. Alternatively, a source of energy cheaper than from coal would dissuade all nations from burning coal, without imposing tariffs or taxes that reduce economic productivity. Affordable electric power can also help developing nations reach modest levels of prosperity and lifestyles that include sustainable birthrates.

The objective for energy cheaper than from coal is $0.03/kWh and a capital cost of $2/watt of generating capacity. How can the liquid fluoride thorium reactor produce energy cheaper than from coal?

Fuel costs. Thorium fuel is plentiful and inexpensive; one ton worth $300,000 can power a 1,000 megawatt LFTR for a year – enough power for a city. Just 500 tons would supply all US electric energy for a year. The US government has 3,752 tons stored in the desert. US Geological Survey estimates reserves of 300,000 tons, and Thorium Energy claims 1.8 million tons of ore on 1,400 acres of Lemhi Pass, Idaho. Fuel costs for thorium would be $0.00004/kWh, compared to coal at $0.03/kWh.

Capital costs. The 2009 update of MIT’s Future of Nuclear Power shows new coal plants cost $2.30/watt and PWR nuclear plants cost of $4.00/watt. The median of five cost studies of molten salt reactors from 1962 to 2002 is $1.98/watt, in 2009 dollars. The following are fundamental reasons that LFTR plants will be less costly than coal or PWR plants.

Pressure. The LFTR operates at atmospheric pressure, without a massive reactor vessel pressurized to 160 atmospheres, and without a large containment dome needed to contain any accidentally released radioactive materials propelled by pressurized steam. One concept for the smaller LFTR containment structure is a concrete building below grade, with a concrete cap at grade level to resist aircraft impact.

Safety. PWRs are safe because of defense in depth – multiple, independent, redundant systems engineered to control faults. LFTR’s intrinsic safety keeps such costs low. A molten salt reactor can’t melt down because the core is already molten — its normal operating state. The salts are solid at room temperature, so if a reactor vessel, pump, or pipe ruptured the salts would spill out and solidify. There is no explosion potential because the pressure in the reactor is atmospheric. If the temperature of the salt rises too high, a solid plug of salt in a drain pipe melts and the fuel drains to a dump tank; the Oak Ridge researchers turned the reactor off this way on weekends.

Heat. The LFTR safely operates at high temperatures. Salt remains liquid below 1400°C; internal graphite core structures maintain integrity even above this. Molten salt heat capacity exceeds that of the water in PWRs or liquid sodium in LMFBRs, allowing more compact heat transfer loops. The molten salt heat exchange loop components of high-nickel metals such as Hastelloy-N are qualified up to 750°C.

Helium gas (green) is successively heated by 700°C molten salt (red) from a LFTR heat exchanger as it passes through high, medium, and low pressure turbines (T). The gas cycles back through three successive compressors (C), cooled by fluid (blue) that transfers rejected heat externally. The recuperator (R) transfers some energy from the compression cycle back to the expansion cycle. The generators (G) produce electricity. (Diagram courtesy of Per Peterson of UC Berkeley.)

Brayton Cycle. The triple reheat closed cycle Brayton turbine achieves a 45% efficiency of conversion from thermal to electric power, compared to 33% typical of existing nuclear and coal power plants using traditional Rankine steam cycles. The Brayton rejected heat to power ratio is thus 1.2 (55/45) rather than Rankine’s 2.0 (67/33) so the cooling requirements are nearly halved, reducing cooling tower costs and making air cooled LFTRs practical in arid regions where water is scarce. This compact Brayton turbine machinery is a quarter the mass, suggesting a similar cost reduction.

Boeing, producing one $200 million airplane per day, is a model for LFTR production.

Mass production. Commercialization of technology leads to lower costs as the number of units increase. Experience benefits arise from work specialization, new processes, product standardization, new technologies, and product redesign. Business economists observe that doubling the number of units produced reduces cost by a percentage termed the learning ratio, seen in the early aircraft industry to be 20%. Today Moore’s law in the computer industry illustrates a learning ratio of 50%. In The Economic Future of Nuclear Power University of Chicago economists estimate the learning ratio is 10% for nuclear power reactors. Boeing, producing one $200 million airplane per day, is a model for LFTR production. Reactors of 100 MW size costing $200 million can be factory produced. Manufacturing more, smaller reactors traverses the learning curve more rapidly. Producing one per day for 3 years creates 1095 production experiences, reducing costs 65%

Research. Cost reductions are presaged by current engineering research. Compact, thin-plate heat exchangers may reduce fluid inventories, size, and cost. Possible new materials include silicon impregnated carbon fiber with chemical vapor infiltrated carbon surfaces and higher temperature nickel alloys. Operating at 950°C can increase thermal/electrical conversion efficiency beyond 50%, and also improve water dissociation to create hydrogen for manufacture of synthetic fuels such as methanol or dimethyl ether that can substitute for gasoline or diesel oil, another use for LFTR technology.

In summary, LFTR capital cost targets of $2/watt are supported by simple fluid fuel handling, high thermal capacity heat exchange fluids, smaller components, low pressure core, high temperature Brayton gas turbine power conversion, simple intrinsic safety, factory production, the learning curve, and new technologies already under development. A levelized $2/watt capital cost contributes $0.02/kWh to the power cost. With plentiful, inexpensive thorium fuel, LFTR can generate electricity at <$0.03/kWh, underselling power generated by burning coal. Producing one LFTR of 100 MW size per day could phase out all coal burning power plants worldwide in 38 years, ending 10 billion tons of CO2 emissions from coal plants now supplying 1,400 GW of electric power. Low LFTR costs are vital to this coal replacement strategy, achievable if this goal is maintained during every design choice. Inexpensive electric power can also assist developing economies to improve prosperity, encouraging lifestyles with sustainable birthrates.