Saturday, August 10, 2013

My Father and the LFTR

A number of years ago I wrote several posts about my father's ORNL career, including his contributions to Molten Salt Reactor chemistry.  My father, Dr. C.J. Barton, Sr., worked at ORNL from 1950 until his retirement in 1977.  He also worked at Y-12 where he made an important contribution to nuclear technology, namely the development of an industrial process for separating Zirconium from Hafnium. Zirconium plays a major role in all conventional reactors.

My study of my father's career lead me to an appreciation of his skills as a scientist.  This in turn has helped me have a better understanding of why certain events took place during his career. In particular, the current focus will be on my father's conversation with Alvin Weinberg which took place in the ORNL cafeteria during the late 1960's.

My father probably misunderstood the implications of the conversation because shortly after it took place the problem he was assigned to solve, namely the separation of Protactinium from molten salt core fluids was taken away from him and assigned to a different division of the laboratory. My father felt disappointed and believed that he had been unfairly treated because he had not received enough support in his division for his research. This probably was the problem that Weinberg thought need addressing by moving the research to another division. The problems that my father was having were related to his division director and Weinberg probably concluded that the problems lay mainly with the division director since his division was broken up and he received a demotion.

It was necessary to separate Protactinium from core fluids in order to produce a Molten Salt Breeder, at least with 1960's ORNL technology.  The alternative, a two fluid breeder would separate blanket salts from fuel salts. Protactinium did not need to be separated from the blanket salts. The problem with the two fluid approach was that it required interlacing tubes for fuel salts and blanket salts. Those tubes would be built using graphite. Graphite shrinks then swells in the presence of intense neutron bombardment which would happen in the core of a Molten Salt Reactor. The so called "plumbing problem" the shrinking of graphite tubes meant that the cores of Molten Salt Reactors would have to be rebuilt every two or three years. One solution to this problem would be to build a large number of small graphite cored Molten Salt Reactors and replace the cores in relays so that one reactor was being repaired while several reactors were producing electricity. This was an approach favored by ORNL in the 1960's and has been revived by LFTR supporters within the last decade.

A second approach was to build a one fluid Molten Salt Breeder Reactor. There was a problem with a one fluid breeder, however. When Thorium is bombarded by neutrons, a nuclear process produces Protactinium which eventually turns into U-233. Protactinium has a love affair with neutrons. It wants to capture them willy-nilly. This leads Protactinium to be transformed into U-234 which is useless as nuclear fuel. Thus, Protactinium is not good for nuclear breeding. In a two fluid reactor, the Protactinium can be shuffled off into a corner until it converts into U-233, but in a one fluid Molten Salt Reactor, Protactinium is likely to have a love affair with a neutron before it can convert into U-233.  For a one salt breeder reactor to work, a method of capturing Protactinium and moving it out of the reactor core must be found.

My father was working on that problem. Alvin Weinberg would have asked my father if he thought the one fluid Molten Salt Breeder was feasible. My father did, although he preferred the two fluid Molten Salt Breeder. The ORNL decision makers, however, wanted to get the highest possible breeding ratio out of their Molten Salt Breed. They believed this could be accomplished with the one fluid breeder. Thus, what they were looking for was confirmation that a one fluid breeder was feasible. Weinberg probable could have gotten the question answered and it seems likely that he would have. Thus, it seems likely that my father made a contribution to the decision to go ahead with the one fluid LFTR.

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