The cost inflation that is effecting the price of all new electrical generating facilities all over the world is a matter of serious concern. If we assume that anthropogenic global warming is going to require the replacement of virtually every carbon based energy source in the world with a carbon-free energy sources that means that most of the world’s generating capacity must be replaced during the next 40 years. The last thing that we need right now is run away inflation of new generator costs. Advocates of renewable energy must face the same inflationary prospects as advocates of nuclear power. The inflation problems of renewable generating system are in some respects worse than the problems of nuclear systems, because renewables use more of the materials that are rapidly increasing in price.
Some forms of carbon-carbon composites do not tolerate neutron radiation well. Thus is by no means certain that carbon-carbons can be used for reactor core structures. Material scientists have by no means given up on carbon-carbons in high neutron environments, and research continues. At the very least carbon-carbons can be used for reactor coolant piping, pumps and heat exchanges in LFTRs. If material scientists can solve the radiation tolerance problem carbon-carbons could be used in reactor cores structure as well.
It should be noted that carbon-carbons are potentially ideally suited for LFTR’s, but if their neutron radiation problem can be solved, they could also be used to build reactor core structures for PBRs as well. The neutron resistant qualities of SiC/SiC composites have been studied and it would appear that some forms of SiC/SiC are fairly neutron resistant. Exactly how resistant remains to be seen. I have yet to see a definitive statement on the compatibility of SiC/SiCs with fluoride salts, yes, but in discussions of their use with fluoride salts, that is usually assumed. I have seen a statement made some 10 years ago about manufacturing difficulties with SiC/SiCs, but I am not aware if the problem was due to a lack of experience, or if it reflected an underlying problem with SiC/SiCs. It is not clear to what extent use of SiC/SiCs would lower reactor-manufacturing costs. However, its use might still be justified even if it proved more expensive, because it could enable reactors to operate at higher temperatures than would be possible with metal components. Thus if SiC/SiCs proved to be relatively expensive to manufacture, their cost might be repaid many times over by the added electrical output produced by greater thermal efficiencies.
Thus carbon-carbon composites are very promising materials for reactor structures involving movement of liquid salts outside reactors, and for heat exchanges. There use in reactor core structures cannot be discounted, but more research and development are required. SiC/SiC composites are promising materials for reactor core structures, and of course, more research is needed. Thus there appears to be a high likelihood that the use of composites would lower the costs of some Generation IV reactor designs, and could prove advantageous for the PBR and could be highly advantageous for the LFTR. Carbon-carbon composites could also be expected to lower reactor costs, and increase transportability of large reactor modules or even complete small reactors, by lowering reactor weight.
It should be noted that that this discussion points to the compatibility of advance materials with generation IV reactors, and in some cases their incompatibility with other well regarded reactor designs. Thus an unexpected consequence of the potential advantages of advanced materials would be a preference for certain Generation IV reactors – the PBR and the LFTR – over LWRs, and LMFBRs.
I would like to express my appreciation to the participants in the Energy From Thorium Engineering Materials Forum for advancing my knowledge and stimulating my thinking about advanced materials. Of course, I picked up the ball and as usual ran with it in a different direction. The Forum members are not responsible for any fumble I might have incurred.
In 1957 Alvin Weinberg presented a paper whose ostensive lead author, Raymond Clare Briant had been dead for three years. This is a procedure is science to memorialize a scientist who had made a significant contribution to a research project but who had died before the contribution could be recorded in a scientific paper. In the paper Weinberg recored:
At the Oak Ridge National Laboratory we have been investigating another class of fluids which satisfies all three of the requirements for a desirable fluid fuel: large range of uranium and thorium solubility, low pressure, and no radiolytic gas production. These fluids, first suggested by R. C. Briant, are molten mixtures of UF4 and ThF4 with fluorides of the alkali metals, beryllium, or zirconium. In order to assess better the possibilities of molten fluoride reactors, ORNL in 1954 constructed and operated a high-temperature, molten-fluoride, circulating-fuel reactor with a BeO moderator and an outlet temperature which ranged above 1500°F (1100 K). The papers which will follow are a description of this reactor. Since the work was supported by the Aircraft Reactors Branch of the U. S, Atomic Energy Commission, the reactor was called the Aircraft Reactor Experiment (ARE).
Later Weinberg, in his autobiography/ was to elaborate Briant’s role not only in the original concept of a Liquid Fluoride Reactor, but in the development of the first Liquid Fluoride Reactor.
ORNL, in the meantime, was gearing up for aircraft nuclear propulsion. At first Cecil Ellis was in charge. Cecil was a physicist who had organized the training of operators at the gaseous diffusion plant in the use of the newly invented helium mass spectrometers for the detection of leaks. He was a born teacher, and he carried out this important job effectively. He was also an optimistic showman: Cecil would adorn his office with large signs summarizing the current main line of the week; I particularly remember a huge sign that touted liquid lithium as the coolant for the indirect cycle. But Cecil, despite his great enthusiasms, was hardly equipped to head ORNL’s aircraft nuclear propulsion project. For this I turned to Ray C. Briant.
Ray was an extraordinary combination of chemical engineer and applied mathematician. When he joined ORNL in 1948 he was about 50 years old. He had spend much of his career in the marble industry and he probably knew more about marble than any other American. During the war he worked at the Johns Hopkins Physics Laboratory with Larry Hafstad, and he came to ORNL at Larry’s suggestion. Ray was brilliant, original and practical. Soon after he arrived I found myself more and more impressed with Ray’s instinct both as a chemist and an engineer. Though Ray arrived about the same time as the TAB convened, he was not a member of the TAB. Instead he spent his time thinking about high-temperature reactors.
Note that I say high-temperature reactors, not aircraft reactors. Ray had little sympathy for the nuclear airplane. Though he was familiar with the arguments proving it was not impossible, he realized that the task was hardly feasible, and he was not convinced that the goal, if achieved, would be very useful. But a reactor operating at high enough temperature to energize chemical reactions – this was a valid, even attractive, goal.
At the time Ray took over, our group had chosen to concentrate on the liquid-metal-cooled indirect cycle. The reactor, basically a souped-up version of the submarine intermediate reactor of General Electric, was to consist of a block of beryllium oxide into which many long, thin cylindrical fuel elements were placed. Liquid sodium, sodium-potassium, or lithium was to flow over the fuel elements and deliver the reactor-generated heat to a heat exchanger. There the heat was picked up by the compressed air that drove the jet engine.
From the beginning, Ray was troubled by the concept. With his great experience with high-temperature materials, Ray could not believe that the fuel elements resembling jackstraws could retain their integrity at a temperature of 1,600 degrees F or higher, under extreme heat fluxes and neutron bombardment. He would ridicule the whole concept, saying, “The damn fuel elements will come out looking like spaghetti!”
Ray tried to visualize a reactor that was not a Swiss watch operating at red, even white, heat. This naturally led him to the notion of liquid fuel: reactors that would have no solid-fuel elements to be deformed. Ray’s idea struck a responsive chord in me, with my attachment to the aqueous homogeneous breeder ideas of Eugene Wigner and Harold Urey.
Raymond Clare Briant’s death in 1954 must have been a significant blow to the ORNL Liquid Salt Reactor research. I have recently been in contact with Briant’s granddaughter, Clare King. She is attempting to develop a more complete picture of her Grandfather. – Charles Barton