Fermi's folly, Wignor's wisdom

Both Eugene Wigner and Enrico Fermi were brilliant scientists. Both made enormous contributions to the theoretical and practical development of atomic energy. Their educational background was different, and for this reason there thinking about long range reactor design diverged. Fermi was a classic physicist. Fermi thought of reactors first in terms of physicis experiments. The CP-1 the ancestor of almost all solid fuel reactors was first of all a physic experiment. Physicists depend on other people to deliver to them the materials they need to conduct their experiments. Once the materials are present, they are assembled, and the physicist then runs his experiment. Bye products from the experiment may be carted off or turned over to other people for reprocessing. The experiment is never designed with easy disposition of byproducts in mind.
Eugene Wigner was trained as a chemical engineer. The orientation of chemical engineers is qyite different from that of theoretical physicists. First theoretical physicists usually think in terms of very large scale entities and events, or in terms of very small scale entities or events. Chemical engineers think of intermediate, human scale objects and events.  The difference in scale and purpose of the events is makes a major difference in the professional outlook of chemical engineers.  Chemical engineers expect to work for profit making enterprises.  For that reason the cost of inputs must be minimized, and the sale of outputs maximized.   The chemical engineer thinks of waste as a potential new profit sources rather than something to be exposed of.   It was, after all an engineer, Herbert Hoover, who introduced the United States to its first war on waste.  The word "Hooverizing" signifies a parcimonious use of resources in order to cut down on waste.  Wigner, who had worked asa a chemical engineer at his father's Tannery, would undoubtedly understood the "Hooverizing" impulse.

Another important aspect of chemical engineering is process and flow.   Chemical engineers seek to produce materials and objects through the transformation of materials throughcomples chemical processes that invlove the flow of chemicals in liquid or gaseous form.  

  

Wigner was a great deal more that a chemical engineer.  He made notable contributions to both chemistry and physics.   Wigner was probably the greatest of all reactor designers.   And eventually the chemical engineer in came to the fore in Wigner.  The fluid core reactor actually predates Fermi's CP-1.    Fermi was interested enough in the early Cavendish reactor experiment to develop  a fluid core reactor at Los Alamos during World War II.  For Fermi the experiment was a dead end, but Wigner realized that the fluid core reactor concept had promise.  

The great flaw of the Fermi reactor was that it used fuel that required expensive and technically difficult chemical processes.  Indeed the fuel required chemical and mechanical processing both before it entered the reactor and after it left the reactor if the fuel was to be reprocessed.  The Fermi solid core reactor concept is at the heart of the so called problem of nuclear waste.   

Wigner, the trained chemical engineer, saw the potential of Fermi's fluid core reactor and along with associates  Alvin Weinberg, Gale Young and Harold Urey developed the concept of a fluid core reactor with a thorium blanket, that could produce electricity at a price that was competative with the price of coal.  The development of the molten salt reactor concept represented a major advance over Wigner's initial heavy water fluid reactor, but it did not significant departure from the concept.  

Fermi was also interested in nuclear breeding, but, unlike Wigner, Fermi saw the problem as a pure physicist, not as a chemical engineer.  Fermi had the poor judgement to pick liquid sodium as his working fluid, and the uranium breeding cycle.   Fermi's rational was that liquid sodium was a poor moderator, thus a sodium cooled reactor would be a reactor would produce fast neutrons.  Plutonium functions best as a nuclear fuel in a fast neuron environment.  The down side to a fast neutron reactor is that it takes a lot of fissionable materials to get a chain reaction going inside one of them.  A more significant disadvantage was the difficulty of working with sodium.  Fermi's Lab, Argonne National Laboratory managed to solve, or at least believes that it solved, the sodium problem, but others were unimpressed with the Argonne solution, and billion of dollars of  have been wasted on unsuccessful sodium cooled reactor projects.    

Fermi chose the sodium cooled fast breeder approach as a physicist, primarily because of its neutron economy.  The downside of the LMFBR is that it uses solid fuel that must be processed at a separate and very expensive chemical reprocessing plant, in an expensive and messy chemical process.  The power produced by the LMFBR would never compete in price with the price of coal.  No doubt the chemical engineers at Argonne do what they are told by the physicists, and don't talk back.  

It is an utter illusion to think that the LMFBR could ever produce electricity at as low a price as the LFTR could.  Nor will the LMFBR ever be as safe.  There is no more reason to assume core breach in a LFTR as in a LMFBR, yet I have demonstrated that a number of safety features could prevent a core breach of a LFTR from ever turning into a disaster.  Not so with the LMFBR.  If there is ever a LMFBR core breech, there would be hell to play.   The notion that Sodium cooled reactors like the Integral Fast Reactor are inherently safe are illusions, as long as they use a fluid sodium coolant.

Liquid metal fast breeders will never hope to compete on construction or electrical production cost with LFTRs , as Eugene Wigner and Alvin Weinberg understood. And Liquid Fluoride salts would never, never, never catch fire.

Many years ago, Alvin Weinberg pointed out the issue of LMFBR safety:

We have no real estimates of accident probabilities for liquid metal fast breeder reactors (LMFBR’s). The Rasmussen estimate (one in 20,000 per reactor year with an uncertainty of five either way) 6 would lead to a meltdown every 3 years. This is probably an unacceptable
rate; an accident rate at least ten times lower, and possibly 100 times lower may be needed if the system is to be acceptable.

Weinberg pointed to another, very significant problem with the LMFBR, the issue of nuclear waste:

Each 5,000 MW LMFBR produces about 75 cubic feet of high-level solidified waste per year, contained i n about 50 steel cans. According to present plans, these would occupy about 1.5 acres of burial space. Thus the entire system of 7,000 reactors would require about 15 square
miles of burial space per year. After 1,000 years, 15,000 square miles level wastes wi l l have decayed sufficiently to allow fresh wastes to be will have been used up; by that time, the radioactivity in the high layered over the older wastes. Thus the 15,000 square miles devoted to high-level wastes might be usable for much longer than 1,000 years.

To summarize, although we cannot identify physical limits that make a world of 7,000 large LMFBR's impossible, one would have to concede that the demands on the technology would be formidable. Two issues appear to me to predominate: first, the acceptable accident rate will probably have to be much lower than the Rasmussen report suggests. If one uncontained core meltdown per 100 years is acceptable (and we have no way of knowing what an acceptable rate really is), then the probability of such an accident will have to be reduced to about one in 1 million per reactor per year. This is the design goal for the LMFBR project in the United States. Second, a nuclear world such as we envisage will have long since had to make peace with plutonium. Ten tons of plutonium per day is mind-boggling. It is hard to conceive of the enterprise being conducted except in well-defined, permanent sites, and under the supervision of a special cadre -perhaps a kind of nuclear United Nations.

I for one do not morn the passing of the Integral Fast Reactor. Sodium cooled reactors are bad ideas as Weinberg subtly suggested. It would be most unfortunate if a sinble cent more is wasted on Fermi's folly.  Let's nail the coffin of the sodium cooled fast breeder shut once and for all.

A Brief History of the Fluid Fuel Reactor: The Aqueous Homogeneous Reactor

The history of the nuclear reactor usually begins with the first successful operation of Enrico Fermi’s Stagg Field reactor on December 2, 1942. In fact scientist working at the Cavendish Laboratory at Cambridge, England built the first successful reactor in 1940. British scientists mixed 112 liters of heavy water with U308 powder inside an aluminum sphere that was 60 cm (2 feet) in diameter. The mixture was mud like and was called slurry. The aluminum sphere was immersed in a bath of heavy mineral oil to serve as a neutron reflector. The British researchers had already found that although a chain reaction was not possible if the U3O8 mixture was suspended in ordinary water, but they were able to witness signs of a chain reaction with heavy water.

During World War II the Canadians were able to successfully produce heavy water so in 1943, Harold Urey and Enrico Fermi suggested repeating the Cavendish experiment. Eugene Wigner became interested in the experiment and began working on an optimal design for a reactor. The original Wigner design called in which the slurry was pumped through a lattice of tubes immersed in a heavy water moderator.

After the value of heavy water as a moderator was better understood, researchers suggested building a large heavy water-uranium slurry reactor as an alternative to the Hanford pile reactors for Plutonium production. The reactor provide top be too great a technological project to be useful as a wartime project. Wigner and other researchers however noted the advantage of using fluoride-uranium salts, rather than U3O8 in the reactors. Of course the mixture of fluoride-uranium salts and heavy water would have created a significant corrosion problem in the reactors.

Beginning in 1943 developed a small aqueous homogeneous reactor was built and operated at Los Alamos. Like the early Cavendish experiment the core of the little reactor was a pot into witch a mud like mixture of water and a uranium compound was poured. Several similar reactors were developed Los Alamos during and after World War II, but eventually Los Alamos scientists began to see the project as a dead end.

Oak Ridge scientists were also interested in the aqueous homogeneous reactor concept during World War II. Meanwhile, Eugene Wigner, who was still in Chicago, had become interested in breeder reactors, and their siblings, converter reactors. Wigner became intrigued by the potential of a thorium breeding cycle. Wigner concerned about future uranium supplies envisioned a reactor that would burn Pu239 and would be surrounded by a blanket of Th232. The reactor would produce U-233, a fissionable nuclear fuel. But, it was noted that the cost of fuel reprocessing for such a reactor would make it not competitive with coal as a power source.

At that point Wigner and Harold Urey realized that the aqueous homogeneous reactor offered a solution to the problem of fuel reprocessing costs. Unlike Fermi who was strictly a classical physicist, Wigner was trained as a chemical engineer. For Wigner, the fluid fuel approach meant that the fuel could be withdrawn without difficulty from the reactor, reprocessed, and returned in a process that would cost much less than the cost of reprocessing solid reactor fuel. It is a tribute to the genius of Eugene Wigner, that he understood the problem that would create nuclear waste in conventional civilian power reactors, and that started the process of developing a solution to the problem.

Wigner, and his bright young assistant, Alvin Weinberg, together with engineer Gale Young, wrote a report outlining the concept in the spring of 1945. Thus the notion that the aqueous homogeneous reactor could serve as a basis for a civilian power industry remained a focus of Wigner for some time. Weinberg, both a research director and later as general director of Oak Ridge National Laboratory, championed Oak Ridge research on the aqueous homogeneous reactor until the end of the 1950’s.

Critics of nuclear power often depict nuclear scientists, as lacking in vision or a concern for human well being, and impractical. In fact the opposite is the case. Eugene Wigner was a scientist who could look long into the future and anticipated resource shortages. He was practical enough to see that low cost power was highly desirable, and as someone who had actually worked as a chemical engineer, he applied a sound chemical engineering approach to the reprocessing of nuclear fuel, and worked that approach back into the design of the reactor. Alvin Weinberg, Wigner’s young assistant, was to learn from Wigner’s long vision, and was to elaborate it during the coming years. Both Weinberg and Wigner were profoundly concerned about human well being, and both saw the possibility that nuclear power could be directed from war to the improvement of the quality of human life.

Sources
ORNL Review, History of Oak Ridge National Labratory, Chapter 4.

Alvin M. Weinberg, "The First Nuclear Era: The Life and Times of a Technological Fixer"

James A. Lane and W. E. Thompson, Fluid Fuel Reactors, Part I, Chapter 1, Addison-Wesley, 1958

Early reactor conceptual developments

Eugene Wigner (left), Enrico Fermi (right)

Some of the best scientist of the 20th century hung around around the "Metallurgical Laboratory" of the University of Chicago. The "Metallurgical Lab" was a cover for the nuclear research establishment which Author H. Compton set up at the University of Chicago during World War II. The Metallurgical Lab was to later give birth to Argonne National Laboratory. The Lab was dominated by two extremely brilliant men, who both made undoubtably made tremendous contributions to establishing the nuclear age. They were the Italian Enrico Fermi, already the holder of a Nobel Prize in Physics, and Eugene Wigner, a Hungarian engineer/physicist who was later to receive a Nobel Prize.

Although no one speaks of a rivalry between the two men, scientist associated with Metallurgical Lab began to form networks around them. After the war Fermi was to lead Argonne National Laboratory, while Wigner took a brief stint as director of the naissant Oak Ridge National Laboratory. It was a young Wigner associate from the Metallurgical Laboratory, Alvin Weinberg, who was to Lead ORNL during its years of glory.

During the war, the atomic energy research establishment quickly expanded.  J. Robert Oppenheimer, of the University of California, organized the Los Alamos team. Fermi was clearly a player in the Los Alamos project.  Wigner focused on reactor development in Oak Ridge and Hanford.   Thus the division of labor between Fermi and Wigner thus made Fermi responsible for the bomb, and Wigner responsible for the reactors.

Weinberg was drawn to Wigner, an became his assistant at the Metallurgical Lab. Both had minds that were not compartmentalized in one discipline.  Wigner was educated as an chemical engineer, and had made significant contributions to theoretical chemistry, but although Wigner never formally studied physics, his is a great name in the history of the discipline.   Weinberg's PhD crossed the lines between physics, math, and biology, and for a brief time before he got caught up in the Manhattan Project, he appeared headed for a career in biology.   Weinberg, who had studied cell devision from the viewpoint of physics and math, was well equipped to understand nuclear fission and the chain reaction. For 35 years, Weinberg stood on the stage of history, and because he was an observant and thoughtful man, he left us an invaluable record of that history. 

It is a mark of Wigner's genius that between 1942 and 1945 Wigner headed both the theoretical-physics research and reactor-engineering and development at the Metallurgical Laboratory. Wienberg was a close Wigner associate. As a reactor developer, Wigner thought like an engineer. Both the original Stagg Field reactor and the ORNL pile reactor were air cooled. It was suggested that the larger Hanford reactors be cooled with helium. He objected to the use of helium as a reactor coolant, because the then existing reactor building materials would not tolerate the high heat found in helium cooled reactors. Wigner decided that the Hanford reactors should be water cooled. Weinberg observed, "making that proposal was a very brave thing for him to do because, at that early time, it had not yet been experimentally demonstrated that any chain reaction was possible. But Wigner had so much confidence in the accuracy of his calculations (backed, of course, by Fermi's experiments) that he insisted that, though the presence of water in the reactor would reduce the multiplication factor by perhaps 3%, enough reactivity would be left to make a reactor of modest size. Moreover, Wigner emphasized that a water-cooled machine could be built much more quickly than a helium-cooled reactor."

A.H. Compton backed Wigner's plan to build the Hanford reactors with water rather than helium cooling. And the Hanford reactors were designed and built as large, water cooled, graphite moderated piles.

The British, despite their participation in the World War II Chalk River project, which developed heavy water reactor technology, were to follow the path which Wigner rejected. Their first reactors were air cooled graphite piles. They were to pay dearly for this technological regression. The infamous Windscale fire, one of the three great reactor accidents in reactor history, was a result of the British use of this primitive technology. The British air and Helium cooled, graphite moderated Magnox reactors, have proven far less durable than American Water cooled reactors, and far more expensive to decommission.

After The Hanford reactor design project was complete. Weinberg states, "there wasn't much left for Wigner's group to contribute to the project, . . ."   In another account of the the period, Weinberg reports, 

We organized a New Piles Committee which met weekly for three months during the spring of 1944. Here the senior luminaries, such as Fermi, Wigner, Szilard, and Franck, together with a few younger assistants like myself, discussed various ideas for reactors: for power, for submarines, for production of plutonium, even for inducing endothermic chemical reactions. Our imaginations ranged widely as we considered various moderators, coolants, and configurations. Inventing a new reactor was an everyday occurrence, simply because no one else had thought about these matters. At that time we were under the impression that uranium would always be scarce.

What happened next was one of the most amazing episodes in the history of science. "Wigner obtained 37 engineering patents on various kinds of reactors: reactors moderated with heavy water, homogeneous reactors, fast reactors, air-cooled research reactors, and water-cooled compact reactors enriched with uranium-235. In all those instances, Wigner served as the spark behind the designs."

Weinberg, of coursed patented the the pressurized water reactor, the basis of naval and civilian power reactors. Farrington Daniels, a chemist in Wigner's reactors group, patented the pebble bed reactor in 1945. Among the reactors that Wigner patented, along with Harry Soodak was the liquid metal fast breeder reactor. Developing the homogeneous reactor became a Fermi project at Los Alamos.

Wigner advocated a homogeneous thorium breeder reactor over his own invention, the Liquid Metal Fast Breeder Reactor. Fermi preferred the fast breeder. The advantage of the homogeneous reactor concept was that it allowed continuous processing of nuclear fuel, and the extraction of fission products, in an environment in which nuclear breeding is possible. Wigner's background in chemical engineering played a critical role in his preference. A liquid core reactor would solve many of the chemical processing problems associated with nuclear breeding. Thorium held numerous advantages over uranium in nuclear breeding. The possibility of a shortage of Uranium was one of the Metallurgical Lab concerns, and breeders were the agreed on solution to that problem. Of course uranium turned out to be anything but in short supply.

The New Piles Committee was anything but short sighted. During a April 26, 1944 meeting, Fermi outlined the plans for a Pu-239 fast breeder that would supply fissionable fuel for other reactors, he noted, "There may be nontechnical objections to this arrangement, for example, the shipment of Pu-239 to smaller consuming plants offers the serious hazard of its falling into the wrong hands."

Weinberg also states that Fermi warned in a New Pile Committee meeting that "for the first time mankind would be confronted with enormous amounts of radioactivity; we must not assume that this will be accepted easily by society."

The devision between Fermi and Wigner about breeding technologies had long term institutional consequences. Fermi's Argonne National Lab developed and championed the LMFBR concept, while Wigner's lab, ORNL, under the leadership of his former assistant, Alvin Weinberg, experimented with homogeneous reactors until the late 1950's before abandoning the technology for the Molten Salt Reactor concept.

The idea for the Molten Salt Reactor originated with V.P. Calkins, Kermit Anderson, and Ed Bettis in about 1947. By 1950, Alvin Weinberg, Warren Grimes, R.C. Briant, and my father, C.J. Barton, Sr. were supporting the project. Although technologically more challenging, the use of liquid salt fuel solved many of the problems associated with homogeneous reactor. The MSR/LFTR concept thus is very much a part of the intellectual heritage of Eugene Wigner, even though he did not invent it.