Published in Coal Strategy Thorium Uranium

8/7/2019 Published in Coal Strategy Thorium Uranium

http://slidepdf.com/reader/full/published-in-coal-strategy-thorium-uranium 1/19

Published in Coal Strategy Thorium Uranium-233 by Kirk Sorensen on January 30th, 2011

The People¶s Republic of China has initiated a research and development project in thoriummolten-salt reactor technology, it was announced in the Chinese Academy of Sciences (CAS)annual conference on Tuesday, January 25. An article in the Wenhui News followed onWednesday (Google English translation). Chinese researchers also announced this developmenton the Energy from Thorium Discussion Forum.

Led by Dr. Jiang Mianheng, a graduate of Drexel University in electrical engineering, thethorium MSR efforts aims not only to develop the technology but to secure intellectual property

rights to its implementation.



This may be one of the reasons that the Chinese have not joined the international Gen-IV effort for MSR development, since part of that involves technology exchange. Neither the US nor Russia have joined the MSR Gen-IV effort either.

A Chinese delegation led by Dr. Jiang travelled to Oak Ridge National Lab last fall to learn moreabout MSR technology and told lab leadership of their plans to develop a thorium-fueled MSR.

The Chinese also recognize that a thorium-fueled MSR is best run with uranium-233 fuel, whichinevitably contains impurities (uranium-232 and its decay products) that preclude its use innuclear weapons. Operating an MSR on the ³pure´ fuel cycle of thorium and uranium-233 meansthat a breakeven conversion ratio can be achieved, and after being started on uranium-233, onlythorium is required for indefinite operation and power generation.



Currently there is no US effort to develop a thorium MSR. Readers of this blog and CharlesBarton¶s Nuclear Green blog know that there has been a grass-roots effort underway for over five years to change this. The formation of the Thorium Energy Alliance and the InternationalThorium Energy Organization have been attempts to convince governmental and industrialleaders to carefully consider the potential of thorium in a liquid-fluoride reactor. There have beenmany international participants in the TEA and IThEO conferences, but none from China.

Chinese energy demand is growing rapidly, and despite the world¶s largest campaign of newnuclear construction, the vast majority of Chinese power generation still comes from fossil fuels.China has abundant supplies of coal, but their combustion has led to some of the worst air qualityin the world. The ability of thorium MSRs to operate at atmospheric pressure and with simplifiedsafety systems means that these reactors could be built in factories and mass-produced. They



could then be shipped to operational sites with standard transportation. Their thorium fuel iscompact and inexpensive. Chinese rare-earth miners have been rumored to have been stockpilingthorium from rare-earth mining for years, and if this is true, the Chinese will have hundreds of thousands of years of thorium already mined and available for use.

The Chinese now have the largest national effort to develop thorium molten-salt reactors.Whether other nations will follow is an open question.

24 Comments »

Google TechTalk Video: ³Save the Uranium-233

Published in Media/Outreach Nuclear Physics Strategy Uranium-233 by Kirk Sorensen on January 28th, 2011

On January 13th I had an opportunity to talk about how we could use the uranium-233 inventoryat Oak Ridge National Lab to start LFTRs and produce the plutonium-238 that we need to power

space probes to explore the solar system. We can also save thousands of lives from the uniqueradioisotopes that we would extract from uranium-233. I hope you enjoy the presentation:

Links to the slides are available here.

9 Comments »

Google TechTalk Slides: ³Save the Uranium-233

Published in Media/Outreach Nuclear Physics Strategy Uranium-233 by Kirk Sorensen on January 21st, 2011

Last week I had another opportunity to give a ³TechTalk´ at Google and I chose to spoke on howsaving the uranium-233 inventory at Oak Ridge could allow us to produce power-generatingradioisotopes to explore space and to extract life-saving medical radioisotopes.

The video might not be ready for a few weeks, so I wanted to go ahead and post the slides.

³Save the Uranium-233 to Save Solar System Exploration´ (PPT with notes, 4.6MB)

I did things a little differently on this presentation than usual, with the slides consisting almosttotally of images and a narration included in notes along with the slides. To enjoy the presentation more in the manner it was given at Google, I recorded a narration, which is a

substantially larger download, but if you¶d like to hear me telling the story this is probably the better one to watch/listen.

³Save the Uranium-233 to Save Solar System Exploration´ (PPT with audio narration,

18.1MB)

I wasn¶t terribly happy with the audio quality of the narration, so if anyone has better ideas or wants to re-record it with better equipment feel free.



11 Comments »

Spectacular LFTR infographic!

Published in Media/Outreach by Kirk Sorensen on January 18th, 2011

I don¶t know who generated this graphic, and I would love to know, because I think it¶s great.

WellHome: Thorium, the Next Generation of Nuclear Power?

(much of the content I recognize because I wrote it initially in a variety of articles«)

Update: I¶ve been contacted by WellHome, and I¶m happy to share some information aboutthem with you:

WellHome¶s energy audits help you understand the systems in your home, how these systems

function on their own, and how they contribute to your whole house comfort and energyefficiency. By testing your home¶s air and duct sealing, insulation levels, and more, WellHome

can evaluate your home¶s energy consumption and heating and cooling efficiency. Home comfort and energy-efficiency improvements don¶t always require extensive updates. All parts of a house,

including duct work, furnaces, air conditioners, insulation, and windows, should work together for maximum home performance.

2 Comments »

Liquid Fuel Nuclear Reactors

Published in Uncategorized by Robert Hargraves on January 9th, 2011

The American Physical Society forum on Physics and Society has just published its quarterlynewsletter, containing two articles about nuclear power, including one by Robert Hargraves andRalph Moir, Liquid Fuel Nuclear Reactors.

Today¶s familiar pressurized water nuclear reactors use solid fuel ² pellets of uranium dioxidein zirconium fuel rods bundled into fuel assemblies. These assemblies are placed within thereactor vessel under water at 160 atmospheres pressure and a temperature of 330°C. This hotwater transfers heat from the fissioning fuel to a steam turbine that spins a generator to makeelectricity. Alvin Weinberg invented the pressurized water reactor (PWR) in 1946 and such units

are now used in over 100 commercial power-producing reactors in the US as well as in navalvessels.

Weinberg also pursued research on liquid fuel-reactors, which offer a number of advantages over their solid-fueled counterparts. In this article we review some of the history, potentialadvantages, potential drawbacks, and current research and development status of liquid-fueledreactors. Our particular emphasis is on the Liquid Fluoride Thorium Reactor (LFTR).



Before describing the characteristics of liquid-fuel reactors we review briefly in this paragraphthe situation with PWRs. In a conventional PWR the fuel pellets contain UO2 with fissile U-235content expensively enriched to 3.5% or more, the remainder being U-238. After about 5 yearsthe fuel must be removed because the fissile material is depleted and neutron-absorbing fission products build up. By that time the fuel has given up less than 1% of the potential energy of the

mined uranium, and the fuel rods have become stressed by internal temperature differences, byradiation damage that breaks covalent UO2 bonds, and by fission products that disturb the solidlattice structure (Figure 1). As the rods swell and distort, their zirconium cladding must continueto contain the fuel and fission products while in the reactor and for centuries thereafter in a wastestorage repository.

Courtesy of Japan Atomic Energy Agency R&D Review 2008Figure 1. Solid fuel rods arestressed by fission products, radiation, and heat.

In contrast, fluid fuels are not subjected to the structural stresses of solid fuels: liquid-fuelreactors can operate at atmospheric pressure, obviating the need for containment vessels able towithstand high-pressure steam explosions. Gaseous fission products like xenon bubble out whilesome fission products precipitate out and so do not absorb neutrons from the chain reaction. LikePWRs, liquid-fuel reactors can be configured to breed more fuel, but in ways that make themmore proliferation resistant than the waste generated by conventional PWRs. Spent PWR fuelcontains transuranic nuclides such as Pu-239, bred by neutron absorption in U-238, and it is suchlong-lived transuranics that are a core issue in waste storage concerns. In contrast, liquid-fuelreactors have the potential to reduce storage concerns to a few hundred years as they would produce far fewer transuranic nuclides than a PWR.

History of liquid fuel reactors

The world¶s first liquid fuel reactor used uranium sulfate fuel dissolved in water. Eugene Wigner conceived this technology in 1945, Alvin Weinberg built it at Oak Ridge, and Enrico Fermistarted it up. The water carries the fuel, moderates neutrons (slows them to take advantage of thehigh fission cross-section of uranium for thermal-energy neutrons), transfers heat, and expandsas the temperature increases, thus lowering moderation and stabilizing the fission rate. Becausethe hydrogen in ordinary water absorbs neutrons, an aqueous reactor, like a PWR, cannot reach



criticality unless fueled with uranium enriched beyond the natural 0.7% isotopic abundance of U-235. Deuterium absorbs few neutrons, so, with heavy water, aqueous reactors can use unenricheduranium. Weinberg¶s aqueous reactor fed 140 kW of power into the electric grid for 1000 hours.The intrinsic reactivity control was so effective that shutdown was accomplished simply byturning off the steam turbine generator.

In 1943, Wigner and Weinberg also conceived a liquid fuel thorium-uranium breeder reactor, for which the aqueous reactor discussed above was but the first step. The fundamental premise insuch a reactor is that a blanket of thorium Th-232 surrounding the fissile core will absorbneutrons, with some nuclei thus being converted (³transmuted´) to Th-233. Th-233, in turn, betadecays to protactinium-233 and then to U-233, which is itself fissile and can be used to refuel thereactor. Later, as Director of Oak Ridge, Weinberg led the development of the liquid fluoridethorium reactor (LFTR), the subject of this article. Aware of the future effect of carbon dioxideemissions, Weinberg wrote ³humankind¶s whole future depended on this.´ The Molten SaltReactor Experiment, powered first with U-235 and then U-233, operated successfully over 4years, through 1969. To facilitate engineering tests, the thorium blanket was not installed; the U-

233 used in the core came from other reactors breeding Th?232. The MSRE was a proof-of- principle success. Fission-product xenon gas was continually removed to prevent unwantedneutron absorptions, online refueling was demonstrated, minor corrosion of the reactor vesselwas addressed, and chemistry protocols for separation of thorium, uranium, and fission productsin the fluid fluorine salts were developed. Unfortunately, the Oak Ridge work was stopped whenthe Nixon administration decided instead to fund only the solid fuel Liquid sodium Metal cooledFast Breeder Reactor (LMFBR), which could breed plutonium-239 faster than the LFTR could breed uranium-233.

The Liquid Fluoride Thorium Reactor

A significant advantage of using thorium to breed U-233 is that relatively little plutonium is produced from the Th-232 because six more neutron absorptions are required than is the casewith U-238. The U-233 that is bred is also proliferation-resistant in that the neutrons that produceit also produce 0.13% contaminating U-232 which decays eventually to thallium, which itself emits a 2.6 MeV penetrating gamma radiation that would be obvious to detection monitors andhazardous to weapons builders. For example, a year after U-233 separation, a weapons worker one meter from a subcritical 5 kg sphere of it would receive a radiation dose of 4,200 mrem/hr;death becomes probable after 72 hours exposure. Normally the reactor shielding protectsworkers, but modifying the reactor to separate U-233 would require somehow adding hot cellsand remote handling equipment to the reactor and also to facilities for weapons fabrication,transport, and delivery. Attempting to build U-233-based nuclear weapons by modifying a LFTR would be more hazardous, technically challenging and expensive than creating a purpose-builtweapons program using uranium enrichment (Pakistan) or plutonium breeding (India, NorthKorea).

Work on thorium-based reactors is currently being actively pursued in many countries includingGermany, India, China, and Canada; India plans to produce 30% of its electricity from thorium by 2050. But all these investigations involve solid fuel forms. Our interest here is with the liquid-fueled form of a thorium-based U-233 breeder reactor.



The configuration of a LFTR is shown schematically in Figure 2. In a ³two-fluid´ LFTR amolten eutectic mixture of salts such as LiF and BeF2 containing dissolved UF4 forms the centralfissile core. (³Eutectic´ refers to a compound that solidifies at a lower temperature than any other compound of the same chemicals.) A separate annular region containing molten Li and Befluoride salts with dissolved ThF4 forms the fertile blanket. Fission of U-233 (or some other

³starter´ fissile fuel) dissolved in the fluid core heats it. This heated fissile fluid attains anoncritical geometry as it is pumped through small passages inside a heat exchanger. Excessneutrons are absorbed by Th-232 in the molten salt blanket, breeding U-233 which iscontinuously removed with fluorine gas and used to refuel the core. Fission products arechemically removed in the waste separator, leaving uranium and transuranics in the molten saltfuel. From the heat exchanger a separate circuit of molten salt heats gases in the closed cyclehelium gas turbine which generates power. All three molten salt circuits are at atmospheric pressure.

Figure 2. In a two-fluid liquid fluoride thorium reactor the fission of U-233 in the core heatsmolten carrier salt (yellow). It attains a noncritical geometry as it is pumped through small passages in a heat exchanger. A separate circuit of molten salt (red), with no radioactivematerials, heats gases in the closed cycle helium gas turbine which spins to generate power.Excess neutrons are absorbed by Th-232 in the molten salt blanket (green), breeding U-233which is removed with fluorine gas. Fission products are chemically removed in the wasteseparator, leaving uranium and transuranics in the molten salt fuel. All three molten salt circuits

are at atmospheric pressure.

LFTRs would reduce waste storage issues from millions of years to a few hundred years. Theradiotoxicity of nuclear waste arises from two sources: the highly radioactive fission productsfrom fission and the long-lived actinides from neutron absorption. Thorium and uranium fueledreactors produce essentially the same fission products, whose radiotoxicity in 500 years drops below that of the original ore mined for uranium to power a PWR. A LFTR would create far fewer transuranic actinides than a PWR. After 300 years the LFTR waste radiation would be



10,000 times less than that from a PWR (Figure 3). In practice, some transuranics will leak through the chemical waste separator, but the waste radiotoxicity would be < 1% of that fromPWRs. Geological repositories smaller than Yucca mountain would suffice to sequester thewaste.

Figure 3. A LFTR produces much less long-lived waste than PWRs. (Adapted from SylvanDavid et al, Revisiting the thorium-uranium nuclear fuel cycle, Europhysics news, 38(2), p 25.)

Existing PWR spent fuel can be an asset. A 100 MW LFTR requires 100 kg of fissile material(U-233, U-235, or Pu-239) to start the chain reaction. The world now has 340,000 tonnes of spent PWR fuel, of which 1% is fissile material that could start one 100 MW LFTR per day for 93 years.

A commercial LFTR will make just enough uranium to sustain power generation, so divertinguranium for weapons use would stop the reactor, alerting authorities. A LFTR will have littleexcess fissile material; U-233 is continuously generated to replace the fissioned U-233, and Th-232 is continuously introduced to replace the Th-232 converted to the U-233. Terrorists couldnot steal this uranium dissolved in a molten salt solution along with lethally radioactive fission products inside a sealed reactor, which would be subject to the usual IAEA safeguards of

physical security, accounting and control of all nuclear materials, surveillance to detecttampering, and intrusive inspections.

It is also possible to configure a liquid-fuel reactor that would involve no U-233 separation. For example, the single fluid denatured molten salt reactor (DMSR) version of a LFTR with no U-233 separation is fed with both thorium and < 20% enriched uranium. It can operate up to 30years before actinide and fission product buildup requires fuel salt replacement, while consumingonly 25% of the uranium a PWR uses.



Starting up LFTRs with plutonium can consume stocks of this weapons-capable material.Thorium fuel would also reduce the need for U-235 enrichment plants, which can be used tomake weapons material as easily as power reactor fuel. U-233, at the core of the reactor, isimportant to LFTR development and testing. With a half-life of only 160,000 years, it is notfound in nature. The US has 1,000 kg of nearly irreplaceable U-233 at Oak Ridge. It is now

slated to be destroyed by diluting it with U-238 and burying it forever, at a cost of $477 million.This money would be far better invested in LFTR development.

Can LFTR power be cheaper than coal power?

Burning coal for power is the largest source of atmospheric CO2, which drives global warming.We seek alternatives such as burying CO2 or substituting wind, solar, and nuclear power. Asource of energy cheaper than coal would dissuade nations from burning coal while affordingthem a ready supply of electric power.

Can a LFTR produce energy cheaper than is currently achievable by burning coal? Our target

cost for energy cheaper than from coal is $0.03/kWh at a capital cost of $2/watt of generatingcapacity. Coal costs $40 per ton, contributing $0.02/kWh to electrical energy costs. Thorium is plentiful and inexpensive; one ton worth $300,000 can power a 1,000 megawatt LFTR for a year.Fuel costs for thorium would be only $0.00004/kWh.

The 2009 update of MIT¶s F uture of Nuclear Power shows that the capital cost of new coal plants is $2.30/watt, compared to LWRs at $4/watt. The median of five cost studies of largemolten salt reactors from 1962 to 2002 is $1.98/watt, in 2009 dollars. Costs for scaled-down 100MW reactors can be similarly low for a number of reasons, six of which we summarize briefly:

Pressure. The LFTR operates at atmospheric pressure, obviating the need for a large

containment dome. At atmospheric pressure there is no danger of an explosion.

Safety. Rather than creating safety with multiple defense-in-depth systems, LFTR¶s intrinsicsafety keeps such costs low. A molten salt reactor cannot melt down because the normaloperating state of the core is already molten. The salts are solid at room temperature, so if areactor vessel, pump, or pipe ruptured they would spill out and solidify. If the temperature rises,stability is intrinsic due to salt expansion. In an emergency an actively cooled solid plug of salt ina drain pipe melts and the fuel flows to a critically safe dump tank. The Oak Ridge MSREresearchers turned the reactor off this way on weekends.

Heat . The high heat capacity of molten salt exceeds that of the water in PWRs or liquid sodiumin fast reactors, allowing compact geometries and heat transfer loops utilizing high-nickel metals.

Energy conversion efficiency. High temperatures enable 45% efficient thermal/electrical power conversion using a closed-cycle turbine, compared to 33% typical of existing power plants usingtraditional Rankine steam cycles. Cooling requirements are nearly halved, reducing costs andmaking air-cooled LFTRs practical where water is scarce.



M ass production. Commercialization of technology lowers costs as the number of units producedincreases due to improvements in labor efficiency, materials, manufacturing technology, andquality. Doubling the number of units produced reduces cost by a percentage termed the learningratio, which is often about 20%. In The Economic F uture of Nuclear Power , University of Chicago economists estimate it at 10% for nuclear power reactors. Reactors of 100 MW size

could be factory-produced daily in the way that Boeing Aircraft produces one airplane per day.At a learning ratio of 10%, costs drop 65% in three years.

Ongoing research. New structural materials include silicon-impregnated carbon fiber withchemical vapor infiltrated carbon surfaces. Such compact thin-plate heat exchangers promisereduced size and cost. Operating at 950°C can increase thermal/electrical conversion efficiency beyond 50% and also improve water dissociation to create hydrogen for manufacture of syntheticfuels such 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 power conversion, simple intrinsic safety, factory production, the learning curve,and technologies already under development. A $2/watt capital cost contributes $0.02/kWh tothe power cost. With plentiful thorium fuel, LFTRs may indeed generate electricity at less than$0.03/kWh, underselling power generated by burning coal. Producing one LFTR of 100 MWsize per day could phase out all coal burning power plants worldwide in 38 years, ending 10 billion tons per year of CO2 emissions from coal plants.

Development Status of LFTRs

A number of LFTR initiatives are currently active around the world. France supports theoreticalwork by two dozen scientists at Grenoble and elsewhere. The Czech Republic supports

laboratory research in fuel processing at Rez, near Prague. Design for the FUJI molten saltreactor continues in Japan. Russia is modeling and testing components of a molten salt reactor designed to consume plutonium and actinides from PWR spent fuel, and LFTR studies areunderway in Canada and the Netherlands. US R&D funding has been relatively insignificant,except for related studies of solid fuel, molten salt cooled reactors at UC Berkeley and Oak Ridge, which hosted a conference to share information on fluoride reactors in September 2010.

Developing LFTRs will require advances in high temperature materials for the reactor vessel,heat exchangers, and piping; chemistry for uranium and fission product separation; and power conversion systems. The International Generation IV Forum budgeted $1 billion over 8 years for molten salt reactor development. We recommend a high priority, 5-year national program tocomplete prototypes for the LFTR and the simpler DMSR. It may take an additional 5 years of industry participation to achieve capabilities for mass production. Since LFTR developmentrequires chemical engineering expertise and liquid fuel technology is unfamiliar to most nuclear engineers today, nuclear engineering curricula would have to be modified to include exposure tosuch material. The technical challenges and risks that must be addressed in a prototypedevelopment project include control of salt container corrosion, recovery of tritium from neutronirradiated lithium salt, management of structural graphite shrinking and swelling, closed cycleturbine power conversion, and maintainability of chemical processing units for U-233 separation



and fission product removal. Energy Secretary Chu expressed historical criticism of thetechnology in a letter to Senator Jeanne Shaheen (D-NH) answering questions at hisconfirmation hearings, ³One significant drawback of the MSR technology is the corrosive effectof the molten salts on the structural materials used in the reactor vessel and heat exchangers; thisissue results in the need to develop advanced corrosion-resistant structural materials and

enhanced reactor coolant chemistry control systems´, and ³From a non-proliferation standpoint,thorium-fueled reactors present a unique set of challenges because they convert thorium-232 intouranium-233 which is nearly as efficient as plutonium-239 as a weapons material.´ He alsorecognized, however, that ³Some potential features of a MSR include smaller reactor sizerelative to light water reactors due to the higher heat removal capabilities of the molten salts andthe ability to simplify the fuel manufacturing process, since the fuel would be dissolved in themolten salt.´

Other hurdles to LFTR development may be the regulatory environment and the prospect of disruption to current practices in the nuclear industry. The Nuclear Regulatory Commission willneed funding to train staff qualified to work with this technology. The nuclear industry and

utilities will be shaken by this disruptive technology that changes whole fuel cycle of mining,enrichment, fuel rod fabrication, and refueling. Ultimately, the environmental and humandevelopment benefits will be achieved only when the cost of LFTR power really proves to becheaper than from coal.

References

Robert Hargraves and Ralph Moir, Liquid Fluoride Reactors, American Scientist, July/August2010

Alvin Martin Weinberg, The first nuclear era: the life and times of a technological fixer.

Springer, New York, 1997.

Oak Ridge National Laboratory document repository

S. David, E. Huffer, H. Nifenecker, Revisiting the thorium-uranium nuclear fuel cycle

David LeBlanc, Molten Salt Reactors: A New Beginning for an Old Idea

Ralph Moir, Edward Teller, Thorium fueled underground power plant based on molten salttechnology,http://ralphmoir.com/moir_teller.pdf

Per Peterson, Pebble Bed Advanced High Temperature Reactor,http://www.nuc.berkeley.edu/pb-ahtr/

Oak Ridge National Laboratory, Fluoride Salt-Cooled High-Temperature Reactor Agenda,https://www.ornl.gov/fhr/agenda.html



A Technology Roadmap for Generation IV Nuclear Systems,http://gif.inel.gov/roadmap/pdfs/gen_iv_roadmap.pdf

Tags: chu, LFTR , molten salt, NRC, Thorium 8 Comments »

³Is Nuclear Waste Really Waste?´

Published in Media/Outreach by Kirk Sorensen on January 5th, 2011

I sure don¶t think so, and I try to make my case in about 20 minutes in a TechTalk I gave atGoogle on November 1 of last year:

7 Comments »

Merry Christmas!

Published in Uncategorized by Kirk Sorensen on December 25th, 2010



³ But the gift of God is eternal life through Jesus Christ our Lord«´



±Romans 6:23

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Not So Fast With Thorium

Published in Uncategorized by Robert Hargraves on December 7th, 2010

Keith Schwartztrauber, a self-declared ³old nuke´, wrote a letter in the November/December 2010 issue of American Scientist , which had published Liquid Fuel Nuclear Reactors by RobertHargraves and Ralph Moir.

To the Editors:

Robert Hargraves and Ralph Moir¶s article ³Liquid 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 thecommercial failures of the thorium-based high-temperature gas-cooled reactor (HTGR) and thedemise of the thorium-based Shippingport light-water breeder reactor (LWBR), however, I don¶tenvision 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 pipecould instantly rupture and release reactor coolant to the containment. It was assumed that largefractions 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) andgraphite-air reactions (yielding fire) in the core.

With the liquid fluoride thorium reactors (LFTRs), a total loss of coolant is equivalent to a totalloss of the liquid core, fuel and blanket materials to the containment. Since the liquid fluorideoperates 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 sucha 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 thematerials would leave the compact geometry that permits criticality. Also the neutron fissioncross sections will reduce as the materials leave the reactor and moderator, thereby hardening theneutron spectra. By design, the reactor room is steel-lined with strongly sloping floors leading todrains. Spilled molten salt would flow to holding tanks designed to treat such an event as³normal´ rather than a big ³accident.´ The continuous chemical processing removes most fission products, especially the gaseous ones that would build up a pressure as they are created, reducingthat 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 nationallaboratories and are used in the aluminum and uranium fuel manufacturing industries, but notwithin today¶s U.S. power reactors. Acceptance of LFTR, ³the chemist¶s reactor,´ will requirenew skills within the NRC, the nuclear industry and the utilities. These LFTR safety featuresrequire validation that can only be achieved by a concerted research and development effort² estimated to cost less than a billion dollars excluding new reactor construction²to bring thetechnology to a level exceeding that already demonstrated at Oak Ridge.

21 Comments »

Alvin Weinberg¶s MSR ³Protohistory´

Published in Uncategorized by Kirk Sorensen on November 11th, 2010



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

The talk was called ³The 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 ³The First Nuclear Era´ doesn¶t say nearly as much about his experienceswith MSR technology as I would have hoped, but it still says the vast majority of what we knowabout what he thought. I have extracted a number of key quotes from the text and kept them in aPPT 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? Iwas 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, andEugene Wigner, the designer of Hanford, both Nobel Prize winners who always argued that weought to investigate whether chain reactors, engineering devices that produced energy from thechain reaction, ought to be basically mechanical engineering devices or chemical engineeringdevices. And Wigner and Urey insisted that we ought to be looking at chemical devices²thatmeans 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 liquidsthat 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 futureof nuclear energy; it was generally believed you that you would have burner reactors such as wehave 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 NationalLaboratory 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 EnergyCommission to divide the breeder business into the plutonium breeder, which was generallyviewed 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 wellto 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 theAtomic 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, asecond-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 EnergyCommission 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. Andthat basically was the reason why the system did not prosper the way it should have, although inthose early discussions there were considerable arguments about which reactor was safer ± thefast 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, TommyThompson, (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.

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