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Thorium Research in the Manhattan Project Era University of Tennessee, Knoxville TRACE: Tennessee Research and Creative Exchange Masters Theses Graduate School 5-2014 Thorium Research in the Manhattan Project Era Kirk Frederick Sorensen University of Tennessee - Knoxville, [email protected] Follow this and additional works at: https://trace.tennessee.edu/utk_gradthes Recommended Citation Sorensen, Kirk Frederick, "Thorium Research in the Manhattan Project Era. " Master's Thesis, University of Tennessee, 2014. https://trace.tennessee.edu/utk_gradthes/2758 This Thesis is brought to you for free and open access by the Graduate School at TRACE: Tennessee Research and Creative Exchange. It has been accepted for inclusion in Masters Theses by an authorized administrator of TRACE: Tennessee Research and Creative Exchange. For more information, please contact [email protected]. To the Graduate Council: I am submitting herewith a thesis written by Kirk Frederick Sorensen entitled "Thorium Research in the Manhattan Project Era." I have examined the final electronic copy of this thesis for form and content and recommend that it be accepted in partial fulfillment of the equirr ements for the degree of Master of Science, with a major in Nuclear Engineering. Ondrej Chvala, Major Professor We have read this thesis and recommend its acceptance: Laurence Miller, Howard Hall Accepted for the Council: Carolyn R. Hodges Vice Provost and Dean of the Graduate School (Original signatures are on file with official studentecor r ds.) Thorium Research in the Manhattan Project Era A Thesis Presented for the Master of Science Degree The University of Tennessee, Knoxville Kirk Frederick Sorensen May 2014 © by Kirk Frederick Sorensen, 2014 All Rights Reserved. ii to my patient and wonderful wife Quincy... iii Acknowledgements I gratefully acknowledge the assistance and patience of Dr. Ondrej Chvala and Dr. Laurence Miller of the University of Tennessee. I also am very grateful for the help that Dr. Jess Gehin of the Oak Ridge National Laboratory provided in helping to procure a paper copy of the third volume of Seaborg's wartime history and several other memos of historical significance. Personnel at Lawrence Berkeley National Laboratory and Oak Ridge National Laboratory also made several historical photographs available for inclusion in this work, and their help is gratefully acknowledged. iv Abstract Research on thorium as an energy source began in 1940 under the direction of Glenn Seaborg at the University of California, Berkeley. Following the discovery of plutonium-239 and its fissile qualities, similar experiments demonstrated that uranium-233 bred from thorium was also fissile. Seaborg viewed uranium-233 as a potential backup to plutonium-239, whose production was one of the Manhattan Project's primary efforts. The central appeal of U-233 was that the chemistry of uranium was well understood, unlike plutonium, but plutonium-239 had the potential to be produced from natural uranium in a critical nuclear reactor. Natural thorium lacked fissile isotopes and so a critical nuclear reactor (to produce U-233) from thorium alone was not possible. Not until the X-10 graphite reactor was constructed at Oak Ridge in 1943 was sufficient U-233 created to conclusively assess its nuclear properties, which were found to be superior to Pu-239 in a thermal-spectrum reactor. Early production of plutonium at X-10 showed significant contamination by Pu-240, which made plutonium unsuitable for simple "gun-type" nuclear weapons. Researchers in the "Metallurgical Laboratory" at the University of Chicago, which included Seaborg's chemistry group, suggested that the plutonium produced be used as a fuel in a special reactor to convert thorium to uranium-233 for weapons. This effort encountered many severe difficulties in fuel fabrication and dissolution. Seaborg also recognized the severe issue that uranium-232 contamination would play in any effort to use uranium-233 for weapons. Through tremendous effort, weapons designers at Los Alamos were able to design workable weapons using the implosion v principle, which accommodated for the impure plutonium produced. Interest in U- 233 for weapons effectively disappeared by 1945, but the Metallurgical Laboratory continued to investigate the potential of a thorium-U-233 "breeder" reactor, based on a homogeneous mixture of uranium salts in heavy water. This effort also came to an end in early 1945. With the end of World War II, the United States was fully focused on growing its nuclear weapons stockpile, and thorium/uranium-233 lacked relevance to that mission as the Manhattan Project concluded at the end of calendar year 1946. vi Preface Historians may one day lament that the discovery of nuclear fission in 1939 by Otto Hahn in Germany and the initiation of World War II by Hitler's Nazi regime took place in such close spatial and temporal proximity. Because of these proximities, the process of nuclear fission was immediately seen as a military threat against the United States by European refugee scientists, many of whom were Jewish or had Jewish relatives. They urged a national response that led to the development of nuclear weapons on an industrial scale without modern precedent. The discovery of fission, along with the advent of powerful particle accelerators in the United States, also made possible the discovery of new elements and new isotopes of existing elements. Their existence and potential was immediately viewed through the prism of war and destruction. This paper is an attempt to understand the early history of thorium as a source of nuclear energy. In discussing thorium, I often refer to the isotope thorium-232 and its fissile daughter product uranium-233 as if they were one material. I realize that they are distinct and the manufacture of uranium-233 depends on neutron absorption in thorium from a source such as a nuclear reactor, but it is also true that thorium-232 is the only significant source of uranium-233, and that energy from uranium-233 is energy from thorium, abstracted by the step of neutron bombardment. There have been scores of accounts written about the early history of the nuclear age, specifically the wartime program code-named the "Manhattan Project" which led to the development of nuclear weapons. These histories focus on the two strands of effort that led to successful nuclear weapons, namely the isotopic separation of U-235 vii from natural uranium and the creation of plutonium in dedicated production reactors fueled by natural uranium. One could easily wonder when the story of thorium as an energy source really began. The official history of the Atomic Energy Commission that covered this era, The New World 1939-1946 (Hewlett and Anderson(1962)), gives scant mention of thorium and its potential, and no details as to the discovery of uranium-233, its fissile nature, nor the potential of thorium as an energy source. Other important works chronicling this time, including Richard Rhodes' Pulitzer- Prize-winning work The Making of the Atomic Bomb, also give little mention to thorium. This can easily be forgiven, for thorium and uranium-233 did not lead to the production of nuclear weapons, but the question of why they did not is a subject that has persistent historical relevance. Today we consider whether thorium is a natural energy source of sufficient magnitude and merit to power human civilization for many hundreds of thousands of years, and it is necessary to understand why decisions were made long ago, and what lessons those decisions could have for us today. This thesis began originally as an attempt to tell the story of the thorium-fueled molten-salt reactor effort at Oak Ridge National Laboratory, strongly motivated by the discovery of a series of books (Seaborg and Loeb(1981), Seaborg and Loeb (1987), Seaborg and Loeb(1993)) written by Glenn Seaborg and Benjamin Loeb covering Seaborg's years as the chairman of the US Atomic Energy Committee. In the last of these, The Atomic Energy Commission Under Nixon (Seaborg and Loeb (1993)), Seaborg describes budget cuts early in the Nixon Administration that led the AEC to curtail research into breeder reactors. He describes how Alvin Weinberg, head of the Oak Ridge National Laboratory (ORNL) and ardent proponent of the thorium- fueled molten-salt breeder reactor (MSBR), argued for the continuation of that line of research. Seaborg goes on to describe how the MSBR program was cancelled in favor of the plutonium-fueled, liquid-metal fast-breeder reactor (LMFBR) but concedes later that that may have been a mistake. (Seaborg and Loeb, 1993, pg.179) viii This significant admission led me to probe deeper into the earlier histories of both the fast-breeder and the molten-salt reactor. At the time of the molten-salt reactor's cancellation, the fast-breeder reactor effort was at a far greater stage of maturity. A commercial fast-breeder reactor called "Fermi-1" had been built near Detroit, Michigan, and had operated briefly in 1966 before suffering a partial core meltdown. (Alexanderson and Wagner(1979)) Fermi-1 had been built using the private funds of a large industrial consortium that included some of the most prominent utilities and nuclear suppliers of the time. In today's funds, it had cost hundreds of millions of dollars. The AEC had facilitated its construction and operation through fee waivers on nuclear fuel and a generous approach to siting and licensing. Several other smaller test reactors, such the Experimental Breeder Reactors -1 and -2 (EBR-1 and -2) and the Southwest Experimental Fast Oxide Reactor (SEFOR) had also been built and operated, with varying degrees of success. There was also a large international effort underway to develop the sodium-cooled fast breeder reactor. In contrast, the effort to develop the molten-salt reactor was much smaller and almost entirely confined to ORNL. Why had there been so much more industrial and governmental interest in the fast breeder than the molten-salt reactor? That search took me further back in history, to the early 1950s when the Fermi project began as a commercial effort under the leadership of Walker Cisler of the Detroit Edison Company.
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