Fast Breeder Reactors : Molten Salt Based

How the Fast Breeder Won the Great Breeder Sweepstake

As must be clear to the reader by now, the earliest ideas about commercial nuclear power were dominated by the mistaken belief that uranium was very scarce. Moreover, in America at least, electricity generated in conventional coal-fired plants was very cheap. Thus we could hardly imagine that nuclear energy based on burning scarce 235U could compete with coal, or if it could, that the necessary uranium ore would last long. As Eugene Wigner put it, the ultimate purpose of nuclear energy was not to replace coal when fossil fuel was abundant; rather it was to substitute for fossil fuel when the latter became scarce. Energy would then be very expensive: nuclear energy based on breeders would be an inexhaustible energy source, and its cost would be perhaps two times the present cost of fossil energy, rather than ten or fifteen times that cost. (Were energy cost to rise so steeply, a large share of our GNP would be spent for energy, and this would reduce our standard of living.)

About this time I wrote two essays on the role of the breeder. The first, "Power Breeding as a National Objective," appeared in Nucleonics in 1958 (vol. 16, no. 8, pp. 75-6): in this piece I argued that current economics alone should not be the sole basis for choosing which reactor system to pursue. Efficient use of the raw materials of nuclear energy—uranium and thorium—was equally important. Indeed it would eventually be more important than estimates of the cost of power. Once inexpensive ores were used up, nuclear power from nonbreeders would be very expensive. This general argument remains valid today, except for one point: if the capital cost of the breeder is too high, the price of uranium ore at which the breeder, with its more efficient utilization of ore, becomes competitive may be extremely high—say, $300 per kilogram. At this price, uranium resources are vast: the breeder can price itself out of business if its capital is too high. Unfortunately, this seems to be the case at the moment, but with Japan and France actively pursuing "power breeding as a national objective," capital costs may come down within the next fifty years.

The other essay, "Energy as an Ultimate Raw Material, or Burning the Rocks and Burning the Sea," appeared in 1959 in Physics Today (vol. 12, no. 11, p. 18). In this essay I speculated on the very long-range future-hundreds, even thousands, of years in the future. Where will our energy come from at that distant time when coal, oil, and natural gas have been used up? Solar energy is one obvious inexhaustible source. Another, if it works, could be controlled thermonuclear energy based on deuterium from the sea (thus "Burning the Sea"). My main point, however, was to stress what Phil Morrison and then Harrison Brown had already noticed: that the residual and all but infinite uranium and thorium in granite rocks could be burned with an energy yield larger than the energy required to mine and refine the ore—but only if breeders, which could burn nearly all the fertile material, are used. I spoke of "Burning the Rocks": the breeder, no less than controlled fusion, is an inexhaustible energy system. Up till then we had thought that breeders, burning 50% instead of 2% of the uranium, extended the energy derivable from fission "only" 25-fold. But, because the breeder uses its raw material so efficiently, one can afford to utilize much more expensive—that is, dilute—ores, and these are practically inexhaustible. The breeder indeed will allow humankind to "Burn the Rocks" to achieve inexhaustible energy!

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.

The fast-breeder project in the United States centered around the Clinch River Breeder, a 250-megawatt sodium-cooled breeder to be built in Oak Ridge by Westinghouse. But, by this time, objections to the breeder were being voiced, ostensibly because the breeder, with its coupled chemical reprocessing system, lent itself to the clandestine diversion of plutonium for nuclear weapons. But in my view the real aim of some of the more dedicated opponents of Clinch River was the extirpation of nuclear energy. The Clinch River Breeder was a handy and vulnerable target, particularly since it could not produce power at a competitive cost. And the opponents eventually won—Clinch River was killed in 1975.

Although the molten-salt system was never allowed to show its full capability as a breeder, a 233U-232Th thermal breeder was demonstrated in Admiral Rickover's Shippingport reactor. Operating with 233U fuel and a thorium blanket, this reactor actually demonstrated a breeding ratio of 1.03—i.e., for every 233U burned, 1.03 new 233U was produced. This accomplishment has gone unnoticed since the cost of power from Shippingport is much higher than from other sources. Whether, as cheap uranium becomes scarce, other reactors will be fueled with 233U and thorium remains to be seen. Thus, as Wigner once said, breeders may emerge from incremental improvements of existing light-water or heavy-water reactors, or may spring from entirely new technologies specifically designed for the breeder. As for fast uranium breeders, the latter path is being followed in France, Japan, India, and Russia. (The French fast breeder PHENIX has demonstrated a breeding ratio of 1.13.) But as for thermal thorium breeders, it seems that these will emerge from the existing nonbreeder LWR or CANDU rather than from molten-salt technology.

Why didn't the molten-salt system, so elegant and so well thought-out, prevail? I've already given the political reason: that the fast breeder arrived first and was therefore able to consolidate its political position within the AEC. But there was another, more technical reason. The molten-salt technology is entirely different from the technology of any other reactor. To the inexperienced, molten-salt technology is daunting. This certainly seemed to be Milton Shaw's attitude toward molten salts—and he after all was director of reactor development at the AEC during the molten-salt development. Perhaps the moral to be drawn is that a technology that differs too much from an existing technology has not one hurdle to overcome—to demonstrate its feasibility—but another even greater one—to convince influential individuals and organizations who are intellectually and emotionally attached to a different technology that they should adopt the new path. This, the molten-salt system could not do. It was a successful technology that was dropped because it was too different from the main lines of reactor development. But if weaknesses in other systems are eventually revealed, I hope that in a second nuclear era, the molten-salt technology will be resurrected.

credit to : http://nucleargreen.blogspot.com/2008/02/how-fast-breeder-won-great-breeder.html