Alvin Weinberg’s MSR "Protohistory"

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

The talk was called “The proto-history of the molten salt system” and it was given by Weinberg on February 23, 1997 to a delegation of Korean scientists visiting Oak Ridge National Lab.

Weinberg’s biography “The First Nuclear Era” doesn’t say nearly as much about his experiences with MSR technology as I would have hoped, but it still says the vast majority of what we know about what he thought. I have extracted a number of key quotes from the text and kept them in a PPT file for some time.

This talk is full of fascinating insights, some of which I have wondered about for years. For instance, who REALLY invented the idea of a nuclear reactor running on liquid fluoride salt? I was pretty sure that it wasn’t exactly Ray Briant, although he led the effort. I had wondered, from what I had read, if some of the K-25 personnel had conceived the idea first.


It was none other than Eugene Wigner himself:

There were two people at the metallurgical laboratory, Harold Urey, the isotope chemist, and Eugene Wigner, the designer of Hanford, both Nobel Prize winners who always argued that we ought to investigate whether chain reactors, engineering devices that produced energy from the chain reaction, ought to be basically mechanical engineering devices or chemical engineering devices. And Wigner and Urey insisted that we ought to be looking at chemical devices—that means devices in which the fuel elements were replaced by liquids. Even in the earliest days people began thinking what kind of liquid would you have in a chain reactor. One of the liquids that was first looked at was slurry of uranium oxide in heavy water, but Wigner was not satisfied with that, and he had one of his people look into whether molten fluorides would be a possibility. So the ideas of molten fluorides first came into the chain reaction community by 1945.

What did the Atomic Energy Commission think of thorium and MSR technology?

In 1962 when there was a big report put out by the Atomic Energy Commission about the future of nuclear energy; it was generally believed you that you would have burner reactors such as we have now or low conversion-ratio converters, and that these would then be gradually replaced by breeder reactors. But at that time we were very careful especially here at the Oak Ridge National Laboratory not to say fast breeder. The word was breeder reactors, not necessarily fast breeders. But Oak Ridge in a way was alone in insisting that thermal breeders, as well as fast breeders, ought to be considered. And there was indeed at that time a tendency within the Atomic Energy Commission to divide the breeder business into the plutonium breeder, which was generally viewed as a fast breeder, and the thorium breeder, and Oak Ridge elected to be the thorium breeder laboratory, because of our history and because the Molten-Salt Reactor lent itself so well to thorium breeding. Now this turned out in retrospect to be, I suppose you say, a political mistake, because the people in Washington were very much influenced by the bulk of the opinion which held that breeder meant fast breeder. Breeder meant sodium cooling. Breeder meant heterogeneous solid fuel element, and for the upstarts in the little town of Oak Ridge, Tennessee, to claim, now wait a minute, there’s another way to go, and this is based on thorium, is based on liquid fuel, that was too far out of the mainstream, and so the thorium breeder, although it was mentioned quite prominently in this 1962 report by the Atomic Energy Commission the thorium breeder never received the political support and the organizational support within the Atomic Energy Commission that the fast breeder received. And therefore, the thorium breeder always has been, until I suppose rather recently, a second-class citizen. What is going to happen now, I don’t know.

And more insight into the quintessential question–why didn’t this happen?

Because the technology was too different from what they were doing then.

I often have asked myself now why was it t his beautiful idea we really had, these wonderful things about these fluid fuels and so on, why is it that the powers that be in the Atomic Energy Commission never quite took the matter fully seriously. And I think the answer is, that the technology of fluid fuel is so different from the technology of solid fuel, the whole question of the maintainability of the system is so many orders of magnitude different than the problem of maintainability of the solid systems, that the people who were prepared to spend hundreds of millions of dollars on fast reactors just couldn’t make that jump. And that basically was the reason why the system did not prosper the way it should have, although in those early discussions there were considerable arguments about which reactor was safer – the fast breeder reactor, heterogeneous, plutonium, the molten salt breeder. And generally speaking, and this was a view that was supported by one of the very important commissioners, Tommy Thompson, (who died in an airplane crash, he was kind of a safety expert for the Atomic Energy Commission), always insisted that the Thorium Molten Salt Reactor was fundamentally safer, than the LMFBR (Liquid Metal Fast Breeder Reactor).

Read the whole thing. It’s in the document repository now.

5 thoughts on “Alvin Weinberg’s MSR "Protohistory"

  1. Thanks for the story Kirk. I hope that someone will invest big in LFTR soon, as it looks to me now, it seems that the Indian three-step-program is to be the first civilian energy from thorium.

    My best Gunnar

  2. Alvin's memory may have been slipping by the time he gave this talk. Ray Briant did not come up with the idea of a Molten Salt Reactor, Ed Bettis and his associates did. I do not doubt that Eugene Wigner at one point fequested that an associate investigate the use of liquid salts in reactors, but nothing came of this, while Bettis had worked up the idea enough to impress Ray Briant, who passed it on to Weinberg.

  3. Out of curiosity, does anyone know what the difficulties with a heavy water/uranium oxide slurry were? Continuing that train of thought, can anyone make an informed guess how a fluidised bed of uranium oxide or carbide and carbon powder would behave?

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