(Posted by Charles Barton, cross posted on Nuclear Green)
Introduction: I wrote Dr, Ralph Moir last week, seeking an email interview. Dr. Moir was an extremely distinguished scientist at Lawrence-Livermore Laboratory, and a personal associate of Dr. Edward Teller. Dr. Moir was extremely gracious in answering all of my questions. I have split the three pasts of the interview into three separate posts. The first questions address Dr. Moir’s work with fission/fusion hybrid reactors.
On Mar 13, 2008, at 9:49 AM, Charles Barton wrote:
Dear Dr. Moir, There are numerous questions I would like to ask you. This would be of course contingent on your willingness to spend the time required to respond to my questions. I take the view that scientists are people who work on important questions, and their views should be known to a broader public. I have posted a number of my father’s public papers along with an account of his career at ORNL on my blog, Nuclear Green. I have also given a considerable focus to the writings and career of Alvin Weinberg. Since you are a senior scientist, your knowledge and experience should be of considerable public interest. If you so choose, I would very much appreciate if you answer some or all of these questions.
During much of your own working career, you worked on the fusion/fission hybrid concept. I have a number of questions in connection with that:
1. Do you still think that concept is viable?
2. What would see as its strengths and weaknesses?
Fusion holds the promise–yet to be fulfilled–of providing a supply of neutrons that can be used to produce fissile fuel for fission reactors. Even if fusion cost twice that of fission per unit of thermal power produced, its fuel would be competitive with mined uranium at $200/kg. Fusion will be even more competitive as its costs come down. This produced fuel can be used in fission reactors to completely burn up the fertile fuel supply, that is depleted uranium or thorium. Its weakness is fusion is not here and past slow progress suggests future progress might be slow. Furthermore, we are not assured that fusion’s costs will be less than twice that of fission.
That fusion can produce or breed fissile fuel is an advantage and simultaneously any facilities must be guarded against their misuse towards making fissile material for unauthorized explosives.
3. What technical advantages, if any would you see for a fusion/fission hybrid over a conventional molten salt reactor?
A conventional molten salt reactor can produce almost all of its own fuel but needs initial fuel for start up and needs some makeup fuel and also some fuel to be used to burnout certain wastes. So the fusion/fission hybrid can be this fuel supplier. In this way the combination of a hybrid fuel supplier and molten-salt burners can supply the planet’s power for many hundreds or even thousands of years at an increased nuclear power level enough to make a big impact in decreasing carbon usage. Such a combination might have one hybrid fusion fission reactor for every fifteen fission reactors.
If a hybrid reactor produces both fuel and power by fissioning this fuel in-situ, I am afraid the system will be uneconomical relative to the combination of a fuel producer and separate burner fission reactors and relative to other fission reactors.
4. In what timeframe might we expect to see an technically and economically viable product?
So far fusion concepts that are approaching the feasibility stage suffer from being very expensive. Tokamak magnetic fusion and laser fusion facilities are very expensive making “productizing” uneconomical based on our present state-of-the-art. The next tokamak called ITER might be built and tested in 15 years and with advances the projected costs in a follow-on might be low enough that a product or viable product can come out after another 15 years or 30 years from now.
The laser fusion facilities are also too expensive but with advances in the next five years a follow-on set of facilities might be an economical product in another 15 years or 20 years from now. A key to progress in fusion is getting better performance in smaller lower cost facilities.
(Posted by Charles Barton, cross posted on Nuclear Green)
1. Can you tell us why you shifted your interest from fission/fusion hybrids to more conventional Molten Salt Reactors?
My job at Lawrence Livermore National Laboratory involved studying and designing fusion/fission hybrid reactors. I led the effort of many terrific researchers including those at other labs: ORNL, ANL, INL, PPPL and industries: Westinghouse, GE, GA, Bechtel. During this time I became increasingly more familiar with all the fission reactor concepts. My favorite technology for fuel production was the use of molten salt pumped through the blanket surrounding the fusion reactor.
My favorite fission reactor was the molten-salt reactor whose program was terminated in the 1970s. While others were forgetting about the molten-salt reactor I became more interested but this was not a part of my job. After retiring from full time work in 2000 I increased my effort on the molten-salt reactor.
2. Why do you think that the Molten-Salt Reactor is important?
It holds the promise of being more economical than our present reactors while using less fuel. I published a paper on this topic that the ORNL people did not feel they could publish. It can come in small sizes without as much of a penalty as is usually the case and can be in large sizes. It can burn thorium thereby getting away from so much buildup of plutonium and higher actinides.
3. What is your relationship to the Fuji Molten-Salt Reactor project?
I became familiar with this effort and its leader Professor Furukawa in about 1980 and appreciate his carrying on the ORNL work after they stopped. He has been a friend and colleague ever since.
4. What project is that project making?
The next step in molten salt reactor development should be the construction and operation of a small <10 MWe reactor based largely on the MSRE that operated at ORNL at about 7 MWth but without electricity production. The FUJI project has not gotten funding and is making no progress other than a paper here and there on some particular aspect.
5. Do you believe that a crash development of the Molten-Salt Reactor concept is warranted?
Yes, that is in fact the conclusion of the paper Teller and I wrote. Surprisingly the cost of a crash program is not so great, less than $1B but its progress could be rapid owing to the feasibility proven by the work at ORNL so long ago on MSRE.
6. What is your opinion of the use of carbon-carbon composites in Molten-Salt Reactors?
I am impressed by the ideas for use of carbon-carbon composites for high temperature heat exchangers and maybe piping and vessels. If metals are not used in the primary system then the temperature could jump from the 700°C of MSRE to 1000°C by use of carbon-carbon composites. This development could be rapid by building on the work taking place in industry today.
7. What is any techniques would you suggest to counteract the effects of neutron radiation of graphite and carbon-carbon composites?
I am not very knowledgeable on graphite technology and can only assume small incremental improvements in its radiation damage abilities can be expected. However, I am intrigued by the dedicated effort of a number of individuals who are studying ways of eliminating the use of graphite as a moderator in the molten-salt reactor. Perhaps carbon-carbon composites might be used as replaceable shields to protect walls from the direct neutron damage or be used to separate two fluids, an old concept at ORNL that was dropped over three decades ago but composites might resurrect it.
(Posted by Charles Barton, cross posted on Nuclear Green)
Questions on Edward Teller
1. Edward Teller remained a controversial figure at the time of his death. Since you worked with Teller, what do you think the public should know, in order to better understand him?
He was brilliant, multi-dimensional and focused. He promoted action via the political process that gave him fame and infamy but most importantly gave results. His writing and that written about him tells the story. It is most inspiring and I recommend its reading to anyone interested.
2. My own understanding of Teller was that he was a complex person. Can you give us some insights?
Yes he was complex but getting to know him told you he was in depth on many axes. He focused on one topic at a time. Sequentially he could switch to another topic but preferred to stay on the topic at hand and work it hard. He treated science as having fun. It was a joy to him to discuss ideas.
3. Teller appears to have had a long time interest in the molten-salt reactor. How important did Teller think the development of the Molten-Salt Reactor was?
Teller had a long term interest in seeing fission reactors built for mankind’s benefit. His interest was to encourage that end rather than work directly in pursuit of reactor development. He strongly favored thorium and thermal reactors and undergrounding them. He periodically over the past 25 years of his life would call on me to review the characteristics of various reactor types. I always treated all of them but ended by saying I preferred the molten-salt reactor. He finally agreed with me and we wrote the paper together. In other words he was not a strong advocate of the molten-salt reactor over a lot of years. He thought the program must have been terminated for good reasons. After examining the reasons for terminating the program he came up with the phrase, “it was an excusable mistake.” He believed building a small molten-salt reactor to get the development going and get deployment going was most urgent because our energy options are running out (especially natural gas).
4. Did Teller have any time frame in which he anticipated to molten-salt reactor development?
At a spending level of $100M per year for R&D and $100M per year for construction, such a program could have a ~10 MWe unit operating in a decade and be well on the way towards a large scale power plan.
5. Teller was interested in setting up reactors underground. Why did he prefer underground placement, rather than using conventional containment structures?
He used the word “obvious” safety. Bomb tests conducted underground contained the radioactive products very well. It was this fact and the fact that waste are to be stored underground both suggest building the reactors themselves underground. I repeatedly brought up the point that under grounding increases the cost and if the cost increase is too much, perhaps over 20% the reactor will most likely not be built. He accepted the idea that 10m underground was a good compromise between the safety benefits of undergrounding while keeping the cost add on small enough to not preclude the deployment.
My web site gives links to downloading my paper with Teller on the thorium-fueled underground power plant based on molten-salt technology. Also there are papers on the cost of electricity compared to other reactors and recommendations for a restart of molten-salt reactor development.
Our world is beset by global warming, pollution, resource conflicts, and energy poverty. Millions die from coal plant emissions. We war over mideast oil. Food supplies from sea and land are threatened. Developing nations’ growth exacerbates the crises.
Few nations will adopt carbon taxes or energy policies against their economic self-interests to reduce global CO2 emissions. Energy cheaper than coal will dissuade all nations from burning coal. Innovative thorium energy uses economic persuasion to end the pollution, to provide energy and prosperity to impoverished peoples, and to create energy security for all people for all time.
We can solve our global energy and environmental crises straightforwardly – through technology innovation and free-market economics. We need a disruptive technology – energy cheaper than coal. If we offer to sell to all the world the capability to produce energy that cheaply, all the world will stop burning coal. It’s as simple as that. Rely on the economic self-interest of 7 billion people in 250 nations to choose cheaper, nonpolluting energy.
Energy is about 7% of the economy. We, and especially developing nations, can not afford to pay much more for energy. Many environmentalists advocate replacing fossil fuel energy with wind and solar energy sources, blind to the fact that these are 3-4 times more costly! Global economic prosperity requires lower energy costs, not higher costs from taxes or mandated costly wind and solar sources. THORIUM: energy cheaper than coal advocates lowering costs for clean energy – a market-based environmental solution.
1 Introduction: an introduction to world crises related to energy and the environment, and the potential for good solutions.
2 Energy and civilization: the relationship between energy, life, and human civilization, easy energy science, life’s dependence on energy flows, civilization’s progress with the energy of the Industrial Revolution, and the 21st century crises of global warming and energy consumption.
3 An unsustainable world: global warming and its terrifying implications for water, agriculture, food, and civilization; depletion of economical petroleum reserves, deadly air pollution from burning coal, increased competition for natural resources from a growing population, and the solution of new energy technology, cheaper than coal.
4 Energy sources: the character and cost of current and principal emerging energy sources: coal, oil, natural gas, hydropower, solar, wind, biomass, and nuclear.
5 Liquid fluoride thorium reactor (LFTR): the history and technology of liquid fuel nuclear reactors, the Oak Ridge demonstration molten salt reactors, thorium, LFTR, the denatured molten salt reactor (DMSR), builders, and possible contenders for energy cheaper than coal.
6 Safety: the safety of molten salt reactors, comparisons to alternative energy sources, radiation risks, waste, weapons, and fear.
7 A sustainable world: environmental benefits of thorium energy cheaper than coal: reduced CO2 emissions, reduced petroleum consumption, synthetic fuels for vehicles, hydrogen power, water conservation, desalination.
8 Energy policy: current confused policies; failure to reduce CO2 emissions, subsidies, recommendations, leadership.
“This book presents a lucid explanation of the workings of thorium-based reactors. It is must reading for anyone interested in our energy future.”
Leon Cooper, Brown University physicist and 1972 Nobel laureate for superconductivity
“As our energy future is essential I can strongly recommend the book for everybody interested in this most significant topic.”
George Olah, 1994 Nobel laureate for carbon chemistry
“Hargraves’ book contains a wealth of information that I’ve never seen anywhere. Very informative and insightful.”
Steve Kirsch, San Jose entrepreneur and philanthropist
“The book describes mankind’s hope for a sustainable and prosperous future: high-temperature thorium-based reactors. The writing is clear and factual, and the book will helpful to anyone interested in energy choices.”
Meredith Angwin, Director of Energy Education for the Ethan Allen Institute
“A terrific book-length description of the need for energy solutions for this century, leading the reader to the advantages of thorium fissioning in a fluid of of molten salt. He explains the technical basis for how such a power plant works and why it can be cheaper than making power from coal — the dominant fuel for power plants today. This book will be a valuable aid for the many people who will take this demonstrated technology of the 1960s at the Oak Ridge National Laboratory in Tennessee through the rebirth phase and into deployment in this century possibly to dominate the power plants by the later part of the 21st century. Another book about why the molten salt reactor development option was abruptly stopped in early 1970s, even though its demonstration was successful and the use of thorium held great promise is Super Fuel by Richard Martin (2012). For background the reader is referred to The First Nuclear Era by Alvin Weinberg (1994).”
Ralph Moir, retired Lawrence Livermore Laboratory physicist, expert in fusion and molten salt reactors
One of the leaders of the MSRP effort was Paul Haubenreich, who was the co-author along with Dick Engel of the journal article “Experience with the Molten-Salt Reactor Experiment” in February 1970. Mr. Haubenreich is a WWII veteran and graduated from the University of Tennessee and the Oak Ridge School of Reactor Technology (ORSORT). Mr. Haubenreich worked on the earlier Homogeneous Reactor Experiment-2 (an aqueous homogenous reactor) and then went on to supervise the construction and operation of the Molten-Salt Reactor Experiment (MSRE).
Sorensen: Please tell me what you just said, about shutting down the Molten Salt Reactor Experiment:
Haubenreich: OK, my recollection is that we had been told that we would have to shut the reactor down in 1969, by the end of 1969, and by the way, the reason that we heard was from an old classmate of mine, Milton Shaw, who was head of reactor development in Washington. He was an enthusiast for the fast breeder reactor. The way I got the story … he called up Alvin Weinberg and says “stop that reactor experiment…MSRE…fire everybody, just tell them to clear out their desks and go home, and send me the money!” Weinberg says “Milt, if we do what you say, you’re going to have to send us more money because we have contracts to pay everybody off, the termination allowances are not in this year’s budget”. And so anyway, the bottom line was that we had to shut down around the end of 1969. We had been together for five years, the crew had, operations, analysis, and maintenance sections. The reactor had first gone critical in June of 1965 and from that time…sometime earlier in ‘65 to late in ‘69 we had kept it hot, salt molten, with around the clock coverage, three shift coverage, 24 hours a day. As the end approached, and the curtain had to come down, it occurred to some of us it might be a nice thing to do to let everybody go home for Christmas. Up to that time we had kept people operating Thanksgiving, Christmas, every Easter weekend and everything else. So, that sounded like a good idea and I said “we have to get this place secured before we can close the door and take the day off”. So everybody agreed to that, we put the salt in the storage tanks and by Christmas day we said “everybody go home, have a good holiday, come back, we’ll see if there’s anything else we need to do”. And that’s what happened, that is my recollection of it, and I guess that’s pretty accurate. We didn’t mean for it to end that way. We had a facility there that we could strip the uranium out of the salt, and had done so with the first charge in which partially enriched U-235 was our fuel for the first… what? 4 years? no, 3 years. And then we loaded in U-233. U-233 had never been used, it had been discovered by Ray Stoughton and Glenn Seaborg –yeah, the chairman of the Atomic Energy Commission at that time, Glenn Seaborg out in California. We stripped the U-235 and U-238 out and put the U-233. The volatility process did not remove plutonium, so we had a smacking of plutonium in the salt at the time, at the last period of operation. This is all very interesting from the dynamics reactor
Paul Haubenreich: Anyway, if you don’t register you can take notes. Anyway, there were 40 of us at Oak Ridge who constituted the student body of the Oak Ridge School of Reactor Technology [ORSORT] and we were enrolled in a program to last twelve months. I don’t know why that’s interesting but — oh yeah, twenty of the forty were new graduates like me, twenty were from the Navy and Milt Shaw had been working for [Admiral Hyman] Rickover and the Navy, we had people from the Electric Boat Company that were overseeing the Nautilus reactor submarine, and from General Electric, Westinghouse, all these people. Twenty of them and twenty recent graduates. Shaw and I were among the forty students in the Reactor Technology. He was a little older and had had the experience with the Navy and I was first-out-of-school and the twenty who were new graduates had the option at the end of their year of ORSORT…they were free agents. Because of the jobs situation and all, each of us got several offers and I was the only one of the twenty that opted to stay at ORNL [Oak Ridge National Laboratory] and a couple of others straggled back later but Shaw went back to Washington and I stayed at ORNL on the Aqueous Homogeneous Reactor Experiment and then with…in 1964 they organized a department at ORNL to do the operations and analysis of the Molten Salt Reactor Experiment [MSRE]. We trained and practiced for the better part of a year and the criticality was achieved during June the first of ‘65. And I guess… when was it? oh!, part of the reason why I was tapped to be the manager of that department was that I had meanwhile turned into a nuclear engineer. I had that year of ORSORT and when the ORNL wanted its engineers to do the Tennessee Professional Engineering Exams, get the PE after their name, I was grandfathered for the Basic Engineering, didn’t have to take that. They said “what branch of engineering do you want to take the test in? You’ve got a bachelors and masters in mechanical engineering” and I said “yeah, but I have the ORSORT stuff so I believe I’ll take it in nuclear engineering”. Well, in the lull between aqueous homogeneous and molten salt UT [University of Tennessee] Knoxville said “we want a Nuclear Engineering department”. My advisor on my Masters in mechanical was Pete Pasqua. He said “I don’t know anything about Nuclear Engineering” they named him to be the head of the department…
Sorensen in the background: was he whom the Pasqua building is named after?
Sorensen: Ok, yeah
Haubenreich: Pete Pasqua. He jumped down to UT from Purdue, just a few years before being my advisor on my Masters thesis. But he came to me and said “can you come up with a curriculum for graduate students in Nuclear Engineering?”, well, yeah, I guess I could, so I had all of my textbooks from ORSORT and knew the people at Oak Ridge and was working out there, so I came up with a one year course in Basic Nuclear Engineering using Glasstone and Edlund
Haubenreich: When I took the [professional engineering] exam at Knoxville, the written exam, I didn’t have much trouble, because I had taught that graduate course in nuclear engineering. And when I went down to Nashville for the oral, they said “Mr. Haubenreich, we have a question: did you see these questions before you took the exam?”
Sorensen laughs hard on the background
Haubenreich: I said “well, in a sense yes”. They said “yes!?” I said “well I taught this course and every one of these questions on your exam are what I gave my students. [Sorensen laughs again] I would’ve been disgraced if I didn’t ace this exam”, which they said “you did!”, I had a perfect score. So anyway that helped to get me the job of managing the Molten Salt Reactor Experiment. But I had some very able people. And I will tell you another little sideline: the operation of the MSRE was not too difficult…wasn’t too burdened with problems…but there’s some. And the people that I had working for me, that was in the 1960s, had grown up, most of them, in East Tennessee, and one of the things they all had besides hound dogs under the porch were old cars out in the yard that didn’t run very well. And every one of these country boys had to learn how to raise the hood and get…uh…fix things. And when 10 or 15 years later they were assigned to the Molten Salt Reactor, if anything came up… we cut the rope on the windlass one time, I’ll tell you about that if you wanna hear it [Sorensen agrees] for sampling and feeding fuel in and… and I said “Oh my goodness, we’re out of business” and they said “we can fix that!” and I said “how are you going to do it” and they said “I don’t know but we will fix it!”, and they did! Several things happened like the time the skunk went to sleep in the trash can and they got him out without having to fumigate the place…a lot of fun things happened. We had a good…well organized… we had a fun time. I went deer hunting a couple of years with my technicians who operated the facility in… so we were almost family, I think. So, it grieved me when at the end of the operation we had to tell some of the people: “we don’t have a job for you anymore”. But that was the way it was.
Sorensen: Can you tell me a little more about Milt Shaw and why it was he instructed them to shut down the experiment?.
Haubenreich: Milton Shaw was sold on the sodium-cooled fast reactor…breeder reactors. And I am not familiar with his… why that was. At the time he was working for Rickover, the Navy was still pursuing the sodium-cooled reactor which went in the Seawolf submarine [SSN 575, not the modern SSN 21] and the pressurized-water reactor that went into the Nautilus. And so, by the late 60s Milt Shaw still had it in his mind that the sodium-cooled reactor which was the type of reactor EBR-I (Experimental Breeder Reactor I) out at Idaho was still viable. But it needed more money to develop it, and so he said “well we can get some money from shutting the Molten Salt Program down”, and as far as I know, that was his idea. But that was a true story I said that Shaw told Weinberg “you gonna have to shut the Molten Salt down and give me some more money for fast breeders”. And the fast breeder persisted for quite a while, as you know…
Sorensen: The money that they were spending on the MSRE, I’ve seen the budget, what they spent on the sodium versus what they spent on molten salt, and the molten salt was a little tiny fraction…
Haubenreich: Oh, yeah, yeah, we were minor-league, money-wise compared to some of the other programs. So we realized that. And I won’t say that the penny-pinching affected our operation any, but it did, we wanted to strip the uranium out and put it back in the hot cell over the next in(?) and do something about the salt where the fission products remained, and they said “well, here’s what you do: Everybody go home, but once a year go by you can heat the salt up and let the [ Sorensen interjects: “fluorine recombine?” ] radiation damage to the frozen salt heal itself. And next year we’re going to have a permanent waste facility in New Mexico”…that was before Yucca Mountain was conceived [the waste disposal proposal to bury at Yucca Mountain long term decaying radioactive waste]. and they said: “We will just take that salt out there to New Mexico and bury it in the salt, in a sodium chloride salt dome and that’ll be a good enough place for it,” that was in ‘69, and we don’t have it yet!. So anyways, the upshot was that “chemical transuranics, you’re redundant, we don’t need you, we’re not going to strip the fission products, we are not going to strip the uranium out of the salt and ship the salt with the fission products to a storage facility” and that’s the way it went. So we were, you might say, forced back into the dugout, shutdown, the game was over, Christmas ‘69.
Sorensen: So, the program continued for a few more years after that.
Haubenreich: Yes it did, and Rosenthal was the director of the Molten Salt Reactor…they gave me a post as assistant director or something like that and I did a lot of spare time work on nuclear safety journal, and the environmental impact statement for Duke’s Oconee plant but three years, in the spring of ‘73, the fusion program needed somebody and so Weinberg told me “you have your pick, you can stay in the fission reactor with Paul Kasten on the gas-cooled reactor, or you can go to fusion”. I thought about it, prayed about it, Mary and I did, and we said I am going to stay with something I know something about…in the fission [program]. A few days after that, Floyd Cutler, who was the associate lab director came in and said “I need to talk to you in private”, and I said “come in Floyd” and he said: “I know we told you you had a choice, but you made the wrong the choice!” [Sorensen laughs] “and I am here to tell you why fusion is better”, he convinced me and I went to fusion. Of course that was a good move. I spent the rest of my… how many years? ‘73 to ‘91 in fusion. But they said “you know how to work with people” and I said “I don’t know anything about…”
Haubenreich: His secretary answered the phone, “Mr. Weinberg’s office”. He was not “stuck up”, we would say in East Tennessee. But he was top notch, he was a good friend of Eugene Wigner. Wigner was another down-to-earth genius and that I had some contact with. He was an advisor on the Molten Salt program. MacPherson was another top-notch person. He didn’t have the recognition that Weinberg and Wigner did. Ask me a question about Weinberg!
Sorensen: Weinberg in his memoir said that he was told he needed to leave Nuclear Energy in the fall of 1972, and in January 1st 1973 he took an extended leave of absence from the lab but he knew… he says in his memoir, that he knew basically…he was being canned. You know? and it was on orders from Chet Holifield [member of the JCAE or Joint Commission on Atomic Energy] and Milt Shaw [Haubenreich says “yeah!”] and what I’m wondering about is how’d you feel and the team feel when you found out that Weinberg was leaving the team?
Haubenreich: That was… I felt let down, I had to say. But I was aware that times had changed. Weinberg was not a convenient but an inconvenient originator of ideas and during the 1950s and 60s his ideas… the climate was such… the timing was such that the AEC [Atomic Energy Commission] gave him a couple of million dollars and said “see what you can do about with that idea” and that was a lot of fun. And Weinberg ran with that ball and thought of another one or two while that was happening and by the early 70s there wasn’t any place for a person with his stature and even though he was extremely well qualified to guide nuclear programs, the AEC, Washington, felt like they had plenty of people up there who could guide the programs “and we want people somewhere down in the laboratories that knew what we want done and not to bother us with all these ideas”. I guess MacPherson was one of the prime advocates of “let’s dig some of this shale that’s underlying East Tennessee and get the thorium out of it! and make U-233 out of it in a reactor!” He said “we’ve got worlds of fuel material, shale has enough thorium in it to make recovery feasible.” Weinberg was… had the… he said… “fluid-fuel reactors are nothing but a pot, a pipe, and a pump” And pumping that kind of stuff around and of course that ignores a lot of reality. The Aqueous Homogeneous Reactor was summarized by one utility executive to come to visit one time, he said: “you’re pumping uranyl sulfate solution at 257 centigrade or a little higher around” and we made enough steam, we’ve got a steam whistle out of a Southern Railroad steam locomotive put one in on the end of our building. We made steam with the Homogeneous Reactor Experiment and piped it up. Everybody had to turn on our last day before everybody had to go home we got to pull the cord, blow that whistle. We got a phone call from over in security the next day “what’s goin’ on over there? We heard that whistle blowing”, [Sorensen laughs] We were just having fun. But anyway, I got sidetracked with the whistle, let’s go back to your chart.
Sorensen: What I was thinking is that you drive a good point here that Weinberg had inconvenient ideas versus the way the Atomic Energy Commission…
Haubenreich: Yeah, I don’t… I wasn’t privy to his latest ideas… by that time “I had my nose in a different book” and so I had the impression that there wasn’t any statement made that… for the staff at ORNL that really gave a good clue as to why he was being… his status was being changed. The impression was that he was doing it under pressure because he was still enthusiastic when he would come to our meetings and gave every impression of thinking we really ought to do something about this…
Sorensen: About? you say “about this”
Haubenreich: Well about the thorium-U233 cycle and the potential of molten salt for being used in that cycle. They were not identical but they were… they had some connection.
Sorensen: So Weinberg was very enthusiastic about thorium and the Molten Salt Reactor?
Haubenreich: I did not detect any diminishing, diminution of his enthusiasm. So, I would feel safe in saying he was still enthusiastic. You would have to ask someone else, Murray Rosenthal about Weinberg’s enthusiasm, but his enthusiasm and his position were not sufficient to get the kind of money that we, Rosenthal, and MacPherson felt like we needed to keep the program going. So when I left in 1973 I was too preoccupied, Herman Posma was a division director at that time, and later became the lab director [in 1974], and Posma kept looking over my shoulder and when I said “I don’t understand this fusion business, I don’t understand how magnetic fields interact with plasma, and how everybody around here seemed pleased when they get a burst of a few seconds in length”, and I said “I’m used to running… we were in the Molten Salt reactor, I think, hot one time–for 10,000 hours, that’s more than a year!–without shutting down and freezing. So, I was… I had a totally different frame of reference”, so for the first couple of years in fusion I would be bothering the physicists, “can you explain to me what’s going on in there, how that works? I don’t get it” –they said “well, you’re too dumb”, [snickering] “well, that may be but until you get some more dumb people on board, you ain’t gonna have a program”, so they had to do that.
Sorensen mutters “tape recorder”, a female voice asks “what is that instrument?”, Sorensen replies “it’s a phone, it’s a phone but it will record your voice and I went and saw Murray Rosenthal and had a great conversation this good with him and I didn’t record it. And I was just kicking myself afterwards”.
Sorensen: “whoa! and I did have a recorder, so I thought if Paul would let me, I’m definitely wanna record it because these reminiscings are precious to have”.
Haubenreich: “Yeah, retrospect is good, I kick myself a couple of days ago. We had a big noise in the night during the wind storm. I looked up and there was a tree sticking down through the roof and the ceiling of the car porch [female voice says: “just missed the car”] and it was a six inch diameter trunk. It’s patched now, they fixed it. But there was this big trunk, came down and stopped this short of the car. And staring back it looked as if there was a tree coming out of the roof, because that treetop would blow out of next door, came down butt-first and rammed through the roof. And the big branches, some of them bigger than my arms held it up and I should have gone out and shot a photograph of that, but I didn’t.”
Sorensen: I really appreciate your time and I don’t want to take too much of it, but there is a question I’d really like to ask: Here we are in 2012 and it’s been a long, long time since you all shut down the MSRE and you’ve had a lot of experiences with fusion, you’ve seen what our country has and has not done with nuclear energy. You’ve seen what we’re doing now burning gas and coal. Looking back on all that, on thorium and MSR, what are your thoughts now looking back, was it a good a idea?, was it a bad idea?, should we have done it? where do we make the right move? [Haubenreich, forcefully: “Molten Salt Reactors!”] …just a big picture, kinda if you could talk to the President and give him some advice, you know, what would you say?
Haubenreich: I think this is a concept whose attractive features are very high temperature source of energy… well maybe I shouldn’t say “very” because there are higher sources, but high temperature and low pressure! [Sorensen: “Yeah!”] Just the opposite of the aqueous homogeneous where we had to have 2000 psi of pressure to keep the stuff from boiling at 300 centigrade. So anyway, I said it has these attractive features. The Atomic Energy Commission through ORNL designed and operated a facility, a device, that was appropriately called a reactor experiment, and its purpose, first principal purpose was to see “can you operate this thing and when it breaks down, can you fix it? can you operate it reliably enough and when it breaks down, can you fix it?” there’s lots of subsidiary questions to that. That reactor experiment operated at high temperature, low pressure from 1965 through 1969 and the answers were positive. I have a notebook down there near my computer. I got congratulations on the successful operations of the MSRE.
So it got some recognition, and the answers were mostly very positive. The materials which had been an Achilles’ heels of the aqueous-homogeneous reactor… …Oh yes! this utility executive who came out and said “if you gave me a stream of hot sulfuric acid and said make steam, make electricity, I would say, I would laugh at you. I would turn it down”. Because we depended on an oxide film on the container material to protect it, to keep it from having catastrophic corrosion.
The Molten Salt Reactor had a container material –let me think–INOR-8, yeah we called it that, Hastelloy-N later, and we had graphite, and we had molten-salt, salt. And the components of each of those three materials in my mind I said “they like to be where they are and they don’t try to attack their neighbors”. So the materials compatibility was a thing that we demonstrated. We pulled out graphite after tens of thousands of hours, I don’t remember, 20 or 30 thousand hours and it looked just like it did when it went in.
There was some sticky points in the operations, the design. The pump worked fine. And the pipes, and we pumped the salt through a radiator, just like on your car. But we didn’t have any anti-freeze and the air was 800 degrees below the freezing point of the fluid, and you were here when the air is 10 degrees below the freezing point of your automobile coolant.
So, anyway, the pipes and everything were red hot, makes nice photographs [Sorensen: “yes, I’ve seen that photograph”] but how do you design a valve to shut off the fuel from the storage site? and the only answer we came up with, before the reactor was built, the experiment was built, was freeze-valves. One of the freeze valves led to a crack in a pipe that released probably a thimble-full of salt into the reactor cell. We detected it immediately. But it was because the freeze-valve was not manufactured to the design, you have a section of the pipe with the salt in it that is flattened and there is a shroud surrounding that section, and you blow air in. And you had baffles to keep the air on the section of the pipe you want. Those baffles are mounted in a sleeve that does not contact the red-hot pipe, and the baffles are thin metal that are not fastened to the pipe, hot pipe, except for a welder that evidently said “look at here, this piece of metal is not welded to the pipe!” and he welded it to the pipe. So, every time you froze and thawed that valve that baffle tried to work the pipe and eventually it cracked. Not bad, but it cracked. And that happened very late in the game. In fact, during the final shutdown period. And we didn’t mess things up. Anyway that’s what happened.
Reminds me the story when they built the gaseous diffusion plant, acres and acres of it, the drawings were not perfect and the craftsmen got tired of interpreting and making them go to the right place and they put compressed air onto the urinals. When you got to do with your business, flushed the urinals and compressed air blew out everything in the urinal out in your face. That’s a true story, I’m told. So that little baffle in the freeze valve was another place where the craftsman thought he knew better than the designer. But the other thing that had us stop for a couple of weeks or more, but less than a month, but a couple of weeks, was the arrangement for putting concentrated fuel salt into the molten salt and dipping samples out for chemical analysis to figure out what’s going on. We had a lot of chemists who wanted to see if it was corroding, and they wanted to take samples periodically. The arrangement was that we had a windlass up here and a can, air-tight can, and we had a flexible steel cable that passes on to the capsule, and I can show you the capsule. And to get it into the business, the reactor, we went through a gate valve, big valve that you’d turn, actually it had a motor that turned it. And the escape valve comes in. One time the cable got tangled up and I said “is it in that gate valve?” –and they said “we don’t know” the driver up here says “it’s far enough down in there it could be on the gate valve, we think we’ve got to hoist it up” and I said “can you put a crank on there instead of that motor and ease that gate valve then and if you run into the cable, could you feel it?” –and they said “we don’t know” it’s got a pretty good mechanical advantage on that drive but after a few days I said “try it and you won’t be fired if things don’t go the way you think”, so they did and they came in “we have bad news, here is the end of that cable” [Sorensen laughs]. Cut off [Sorensen: “oh-oh”] “the sample capsule is down in the pump, it’s on a cage and here is the raw end of the cable up here”.
So I said “what are we going to do?” and there’s the good old boys for you, they said “we’re go in there and fish that thing out, with the cable, and we’ll make another one, put it in there and not get it tangled up next time” I said “you’re kidding, what does it look like down in there?”, they said “we don’t know”. I said “is there such a thing as fiber optics?” “fiber optics? I’ve heard of that” and at that time the only manufacturer of fiber optics only made lengths like 50, 60 ft. long. but we made up a viewing device, that would be put down in there, and there’s the capsule. “Can we make up something to hang on to cable, that would grab that cable, on the capsule, and let us pull it out?”, they said “let us think about that” and they thought about it and came up with something, and they fished that capsule out and we were back in business after a while.
But that was a little sore point … so, the freeze valve, sampling and fuel addition are such thorny problems, though not surprising, that at the end of the experiment we got problems with them.
So, back to the question, what would I tell the President? I would say that we worked for several years on an experiment that in our estimation proved what it went out to prove, that you can handle this molten salt reliably and when things go wrong, the things that went wrong with us, anyway, we were able to fix. And that the dynamics, the chemistry, the materials situation was better than anybody, well except enthusiasts might have dreamed that it might be that good, but everybody else was sure to have their fingers crossed. Anyway, it turned out wonderful materials-wise. The freezing, we had a radiator that blew air across the red-hot tubes with the salt on them and the air went up a big stack. And in the wintertime, when it was bitter cold, all the birds in Anderson County perched at the top of that stack to get warm, meanwhile down there it was red hot, but up there it was just nice. But that worked for years, it never froze up. The radiator never froze. So, that was one that was more of a challenge than the freeze valves, but the freeze valves had a glitch and the radiator didn’t. At one time we had to scram, we had doors that dropped down on either side of the radiator, salt still going through, to stop the air flow. And the big doors made by Joy Blower Company had a hub that was about this big of cast aluminum, big veins that went around and I was down at scout camp and they didn’t bother to tell me that hub blew up! [Sorensen: “I’ve heard that story, yeah”], it cracked and pieces went everywhere. So the doors dropped down like they were supposed to, we got the salt down in tanks, cooled it down, went in and inspected it, there weren’t any crumbs of the blower hub on the hot tubes, the tubes that would be red-hot. We thought that might be a problem, but that ended up alright after a while. Joy had made a lot of these same blowers for NASA, and they were fine.
Anyway, my word to the President would be, in my opinion, the potential, the advantages outweigh the difficulties and the concept is ultimately going to be a practical application, so that’s my bottom line. [Sorensen: well, good!, good... I’m getting stuff on that, thank you, thank you!]
Sorensen Note: Many thanks to Eduardo Madrid for the transcription of the interview.
I really enjoyed watching Alex Pasternack’s new short video on Dr. Edward Teller:
Ralph Moir had told me this story about Teller before, but watching it presented this way with the video interviews of Teller and short descriptions of projects that we worked on, was much richer. Teller was indeed a very unique kind of person, whose early experiences with Communism in Hungary shocked his mind into responses that others struggled to understand. I hesitate to cast any judgements since I certainly did not go through what Teller went through, but I have noticed that among Hungarian emigres to the US of a particular age (and I have met several) there is an intensity of personality that I have come to believe must be a product of this environment.
In posting this, I went back to reference an earlier post I had made for Alex’s previous effort, “The Thorium Dream”, and discovered to my horror that I had never posted it on the blog! So in attempting to rectify for that past oversight, here is his enjoyable short documentary on the growing effort to bring an understanding of thorium and the molten-salt reactor to the world.
Finally, Moir references the paper that he and Teller co-wrote, which was Teller’s final paper. For those of you who would like to read it, here it is in PDF form:
Thorium-Fueled Underground Power Plant Based on Molten Salt Technology, by Ralph Moir and Edward Teller, 2004
September 26, 2011
Huntsville, Ala. – Flibe Energy Inc. has named six members to the Flibe Energy Board of Advisors. The board members will provide direction and guidance in the continued development and commercialization of the liquid fluoride thorium reactor or LFTR (pronounced “lifter”).
Flibe Energy Inc. is the leader in development of LFTR technology, which harnesses the energy stored in thorium, the Earth’s most abundant and dense natural energy source. A small handful of thorium can supply a lifetime’s energy needs, a small grain silo of thorium could power North America for a year and known thorium reserves could power society for thousands of years.
LFTR can produce not only safe, sustainable electricity, but lifesaving medical radioisotopes, desalinated water and ammonia for agriculture and synthesized fuels in the process. LFTR technology will have tremendous impacts in global energy, medical, agricultural and industrial sectors. Read about the board members…
In trying to answer the persistent question about LFTRs: “why wasn’t this done before?” I’ve obtained a report from 1962 made to President Kennedy where future development options for nuclear power were laid before him. Alvin Weinberg specifically references this report in his 1994 memoir (“First Nuclear Era”) and goes on to say that it recommends both the plutonium fast-breeder reactor and the liquid-fluoride thorium reactor as technologies that should be developed. Here’s what Weinberg had to say in his book:
“Until then I had never quite appreciated the full significance of the breeder. But now I became obsessed with the idea that humankind’s whole future depended on the breeder. For society generally to achieve and maintain a living standard of today’s developed countries depends on the availability of a relatively cheap, inexhaustible source of energy. (As I write these words, I realize that until recently I tended to dismiss solar energy as too expensive, and fusion as probably infeasible. I really don’t know whether this will always be the case.)
“The breeder became central in my thinking about nuclear-energy development. And, with Glenn Seaborg’s becoming the chair of AEC in 1960, the breeder acquired ever-increasing status with AEC—especially recognition as an essentially inexhaustible source of energy.
“In 1962, the AEC issued a report to the president on civilian nuclear power. Lee Haworth, a superbly responsible physicist-administrator, was in charge of drafting the report. He projected a nuclear deployment by 2000 of about 700 gigawatts (compared with the actual deployment in 1993 of 102 gigawatts), which seemed at the time quite reasonable. Both the fast breeder based on the 239Pu-238U cycle and the thermal breeder based on the 233U-232Th cycle figured prominently in the report. Indeed, the report implied that both systems should be pursued seriously, including large-scale reactor experimentation. It particularly favored molten uranium salts for the thermal breeder. But the molten-salt system was never given a real chance. Although the AEC established an office labeled “Fast Breeder,” no corresponding office labeled “Thermal Breeder” was established. As a result, the center of gravity of breeder development moved strongly to the fast breeder; the thermal breeder, as represented by the molten-salt project, was left to dwindle and eventually to die.”
At any rate, I have obtained a copy of this report and scanned it and made it available as a PDF. I think it is worthy of our study in an attempt to figure out why decisions were made that led us to the current situation.
Here are some interesting passages from the report:
In the thorium-uranium-233 cycle, the situation is quite different. U-233 emits more neutrons in thermal fission than does U-235; on the other hand, it is only slightly better in fast fission than in slow. Hence, thermal breeders offer greatest promise, minimizing as they do the power density and fuel endurability requirements. However, thermal breeders have a different complication in that fission products act as strong absorbers of slow neutrons, requiring that these products not accumulate too much. Among the most promising solutions of this difficulty is to use the fuel in fluid form, thus permitting continuous extraction and reprocessing to remove the fission products. Various fluid fuels have been studied for this purpose. The currently most promising approach is the use of fused uranium salts which can be circulated, both for reprocessing purposes and for heat transport. This technology is, however, in a fairly early stage.
Even when breeder reactors become economic and begin to be installed there will be a complication regarding fuel supplies. At least for some time to come, economic breeders will have breeding gains so low that they will produce not more than 3% or 4% of their fuel inventory each year. Hence, since the annual growth in energy consumption is about 6%, it will be necessary, if nuclear power increases its fractional share of the total load, to fuel some portion of the installations with fissionable uranium-235.
This leads to no great problem in the thorium-uranium thermal breeders. The fuel demand can be fulfilled simply by charging some of them, initially at least, with U-235, though at some sacrifice in economics and in the amount of U-233 that they produce.
On the other hand the “fast” reactors required to breed an excess of plutonium are economically attractive only when plutonium rather than U-235 is used to fuel them. Hence the most promising arrangement for incorporating them in a rapidly expanding nuclear power economy would undoubtedly be to use thermal converters to help provide the plutonium needed for added installations. This combination would continue until increases in the relative “yield” of plutonium from the breeders, together with a lower relative rate of growth of electrical energy consumption enabled the breeders to catch up and produce enough plutonium by themselves.
We get somewhat of an insight into the thinking of the Atomic Energy Commission with regards to breeder reactors. If they were to use uranium-plutonium, then plutonium supplies were crucial due to the fact that each fast breeder needed 10 to 15 times as much fissile material to generate a unit of power as a thermal reactor did. The light-water reactors at the time were producing plutonium as a byproduct. The fast-breeder needed and wanted that plutonium. Reactors like LFTR needed a tiny fraction of the fissile inventory as the fast breeder did and could be started on HEU.
Here’s an image of how the AEC envisioned light-water reactors running on enriched uranium and producing plutonium, and fast-breeder reactors needing that plutonium, working together.
The picture begins to become clearer, especially when we consider how Weinberg described what the AEC did with this report, establishing a “Fast Breeder” office but no “Thermal Breeder” office.
More thoughts on this later…
The American Physical Society forum on Physics and Society has just published its quarterly newsletter, containing two articles about nuclear power, including one by Robert Hargraves and Ralph Moir, Liquid Fuel Nuclear Reactors.
Today’s familiar pressurized water nuclear reactors use solid fuel — pellets of uranium dioxide in zirconium fuel rods bundled into fuel assemblies. These assemblies are placed within the reactor vessel under water at 160 atmospheres pressure and a temperature of 330°C. This hot water transfers heat from the fissioning fuel to a steam turbine that spins a generator to make electricity. 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 naval vessels.
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, potential advantages, potential drawbacks, and current research and development status of liquid-fueled reactors. Our particular emphasis is on the Liquid Fluoride Thorium Reactor (LFTR).
Before describing the characteristics of liquid-fuel reactors we review briefly in this paragraph the situation with PWRs. In a conventional PWR the fuel pellets contain UO2 with fissile U-235 content expensively enriched to 3.5% or more, the remainder being U-238. After about 5 years the 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, by radiation damage that breaks covalent UO2 bonds, and by fission products that disturb the solid lattice structure (Figure 1). As the rods swell and distort, their zirconium cladding must continue to contain the fuel and fission products while in the reactor and for centuries thereafter in a waste storage repository.
In contrast, fluid fuels are not subjected to the structural stresses of solid fuels: liquid-fuel reactors can operate at atmospheric pressure, obviating the need for containment vessels able to withstand high-pressure steam explosions. Gaseous fission products like xenon bubble out while some fission products precipitate out and so do not absorb neutrons from the chain reaction. Like PWRs, liquid-fuel reactors can be configured to breed more fuel, but in ways that make them more proliferation resistant than the waste generated by conventional PWRs. Spent PWR fuel contains transuranic nuclides such as Pu-239, bred by neutron absorption in U-238, and it is such long-lived transuranics that are a core issue in waste storage concerns. In contrast, liquid-fuel reactors 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 Fermi started it up. The water carries the fuel, moderates neutrons (slows them to take advantage of the high fission cross-section of uranium for thermal-energy neutrons), transfers heat, and expands as the temperature increases, thus lowering moderation and stabilizing the fission rate. Because the 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 unenriched uranium. 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 by turning 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 in such a reactor is that a blanket of thorium Th-232 surrounding the fissile core will absorb neutrons, with some nuclei thus being converted (“transmuted”) to Th-233. Th-233, in turn, beta decays to protactinium-233 and then to U-233, which is itself fissile and can be used to refuel the reactor. Later, as Director of Oak Ridge, Weinberg led the development of the liquid fluoride thorium reactor (LFTR), the subject of this article. Aware of the future effect of carbon dioxide emissions, Weinberg wrote “humankind’s whole future depended on this.” The Molten Salt Reactor Experiment, powered first with U-235 and then U-233, operated successfully over 4 years, 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 unwanted neutron absorptions, online refueling was demonstrated, minor corrosion of the reactor vessel was addressed, and chemistry protocols for separation of thorium, uranium, and fission products in the fluid fluorine salts were developed. Unfortunately, the Oak Ridge work was stopped when the Nixon administration decided instead to fund only the solid fuel Liquid sodium Metal cooled Fast 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 case with U-238. The U-233 that is bred is also proliferation-resistant in that the neutrons that produce it 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 and hazardous 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 protects workers, but modifying the reactor to separate U-233 would require somehow adding hot cells and 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-built weapons program using uranium enrichment (Pakistan) or plutonium breeding (India, North Korea).
Work on thorium-based reactors is currently being actively pursued in many countries including Germany, 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 “two-fluid” LFTR a molten eutectic mixture of salts such as LiF and BeF2 containing dissolved UF4 forms the central fissile core. (“Eutectic” 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 Be fluoride salts with dissolved ThF4 forms the fertile blanket. Fission of U-233 (or some other “starter” fissile fuel) dissolved in the fluid core heats it. This heated fissile fluid attains a noncritical geometry as it is pumped through small passages inside a heat exchanger. Excess neutrons are absorbed by Th-232 in the molten salt blanket, breeding U-233 which is continuously removed with fluorine gas and used to refuel the core. Fission products are chemically removed in the waste separator, leaving uranium and transuranics in the molten salt fuel. From the heat exchanger a separate circuit of molten salt heats gases in the closed cycle helium gas turbine which generates power. All three molten salt circuits are at atmospheric pressure.
LFTRs would reduce waste storage issues from millions of years to a few hundred years. The radiotoxicity of nuclear waste arises from two sources: the highly radioactive fission products from fission and the long-lived actinides from neutron absorption. Thorium and uranium fueled reactors 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 from PWRs. Geological repositories smaller than Yucca mountain would suffice to sequester the waste.
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 diverting uranium for weapons use would stop the reactor, alerting authorities. A LFTR will have little excess 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 could not 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 detect tampering, 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 30 years before actinide and fission product buildup requires fuel salt replacement, while consuming only 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 to make weapons material as easily as power reactor fuel. U-233, at the core of the reactor, is important to LFTR development and testing. With a half-life of only 160,000 years, it is not found 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. A source of energy cheaper than coal would dissuade nations from burning coal while affording them 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 generating capacity. 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 Future 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 large molten salt reactors from 1962 to 2002 is $1.98/watt, in 2009 dollars. Costs for scaled-down 100 MW 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 intrinsic safety keeps such costs low. A molten salt reactor cannot melt down because the normal operating state of the core is already molten. The salts are solid at room temperature, so if a reactor 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 in a drain pipe melts and the fuel flows to a critically safe dump tank. The Oak Ridge MSRE researchers 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 sodium in 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 using traditional Rankine steam cycles. Cooling requirements are nearly halved, reducing costs and making air-cooled LFTRs practical where water is scarce.
Mass production. Commercialization of technology lowers costs as the number of units produced increases due to improvements in labor efficiency, materials, manufacturing technology, and quality. Doubling the number of units produced reduces cost by a percentage termed the learning ratio, which is often about 20%. In The Economic Future 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 with chemical vapor infiltrated carbon surfaces. Such compact thin-plate heat exchangers promise reduced 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 synthetic fuels 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 to the 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 MW size 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 theoretical work 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 salt reactor 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 are underway 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 to complete 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 development requires 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 to such material. The technical challenges and risks that must be addressed in a prototype development project include control of salt container corrosion, recovery of tritium from neutron irradiated lithium salt, management of structural graphite shrinking and swelling, closed cycle turbine power conversion, and maintainability of chemical processing units for U-233 separation and fission product removal. Energy Secretary Chu expressed historical criticism of the technology in a letter to Senator Jeanne Shaheen (D-NH) answering questions at his confirmation hearings, “One significant drawback of the MSR technology is the corrosive effect of the molten salts on the structural materials used in the reactor vessel and heat exchangers; this issue results in the need to develop advanced corrosion-resistant structural materials and enhanced reactor coolant chemistry control systems”, and “From a non-proliferation standpoint, thorium-fueled reactors present a unique set of challenges because they convert thorium-232 into uranium-233 which is nearly as efficient as plutonium-239 as a weapons material.” He also recognized, however, that “Some potential features of a MSR include smaller reactor size relative to light water reactors due to the higher heat removal capabilities of the molten salts and the ability to simplify the fuel manufacturing process, since the fuel would be dissolved in the molten 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 will need 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 human development benefits will be achieved only when the cost of LFTR power really proves to be cheaper than from coal.
Robert Hargraves and Ralph Moir, Liquid Fluoride Reactors, American Scientist, July/August 2010
Alvin Martin Weinberg, The first nuclear era: the life and times of a technological fixer. Springer, New York, 1997.
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 salt technology,
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,
A Technology Roadmap for Generation IV Nuclear Systems, http://gif.inel.gov/roadmap/pdfs/gen_iv_roadmap.pdf
The July/August 2010 issue of American Scientist magazine has a ten-page article, Liquid Fluoride Thorium Reactors, by Robert Hargraves and Ralph Moir. The article ends with a link to this web site, so welcome to you and other newbies.
This redesigned site is rich with information; here’s a guide for those with inquiring minds. Start at the very top of the page at the eight links in lower case separated by bars. Click on “about” for a short introduction to thorium, the research history, and a graphic representation of the liquid fluoride thorium reactor, LFTR.
Click “msrp” to read the summary of the molten salt research program at the Oak Ridge National Laboratories in 1958-1976, where these nuclear reactors ran. Click “plan” to read Kirk Sorensen’s vision of a deployment strategy that starts up a global fleet of LFTRs using up the fissile material from spent fuel “waste” and excess weapons.
In the right hand column under “Pages” are a timeline, a LFTR fuel cycle summary, and a plea to save the DOE’s U233 slated to be destroyed.
Under “Top Links” is the cited online forum, where engineers and scientists openly exchange ideas about LFTR technology. If you would like to contribute your knowledge, spend some time reading the posts in your area of expertise, register, and post.
Also under “Top Links” is the rich “PDF Document Repository” which is an index of all the LFTR R&D done by Oak Ridge National Laboratories, plus many recent papers by current researchers worldwide.
Scroll down to explore more of the right hand column links, pausing at “Archives” to peruse earlier posts to this blog.
Welcome to American Scientist readers and all newbies at Energy from Thorium.