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General Kenneth Nichols and the Manhattan Project
Nichols
The Oak Ridger has published the latest in a series of articles about General Kenneth D. Nichols, the Manhattan Project, and the 1954 Atomic Energy Act. The series has been produced by Nichols’ grandniece Barbara Rogers Scollin and Oak Ridge (Tenn.) city historian David Ray Smith. Gen. Nichols (1907–2000) was the district engineer for the Manhattan Engineer District during the Manhattan Project.
As Smith and Scollin explain, Nichols “had supervision of the research and development connected with, and the design, construction, and operation of, all plants required to produce plutonium-239 and uranium-235, including the construction of the towns of Oak Ridge, Tennessee, and Richland, Washington. The responsibility of his position was massive as he oversaw a workforce of both military and civilian personnel of approximately 125,000; his Oak Ridge office became the center of the wartime atomic energy’s activities.”
Isao Murata, Shigeo Yoshida, Akito Takahashi
Fusion Science and Technology | Volume 36 | Number 2 | September 1999 | Pages 181-193
Technical Paper | doi.org/10.13182/FST99-A101
Articles are hosted by Taylor and Francis Online.
Heavy concrete is a promising candidate material for a fusion reactor shield. It provides strong shielding performance, though it has a heterogeneous structure due to random arrangement of the heavy aggregates contained as absorbers. To obtain data for future fusion reactor shield designs, D-T neutron irradiation experiments using both heterogeneous and homogeneous heavy concrete samples were carried out to investigate how much the heterogeneity due to the aggregates affects shield performance. Leakage neutron spectra and reaction rates of activation foils were measured, and they were compared with the analyses by the Monte Carlo code MCNP-CFP. From the comparison of results, the measured heterogeneity effect was well reproduced by MCNP-CFP, though there was a slight disagreement in the thermal region. For a point neutron source, a heterogeneous shield was found to be advantageous compared with a homogeneous one from the standpoint of shielding performance above 1 MeV. This conclusion was exactly opposite to what was anticipated. Analysis of the results confirmed that the effect was strongly associated with the manufacturing process used for the heavy concrete. For thermal neutrons, a homogeneous shield is still regarded to be most preferable. To suppress the heterogeneity effect above 1 MeV, it is necessary to use a sufficiently large heavy concrete shield. Then analysis with a conventional calculation method is feasible except for the thermal neutron region. If a smaller shield is employed, a specialized Monte Carlo code with a heterogeneous treatment like MCNP-CFP should be used for the precise analysis.