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Thermal Hydraulics
The division provides a forum for focused technical dialogue on thermal hydraulic technology in the nuclear industry. Specifically, this will include heat transfer and fluid mechanics involved in the utilization of nuclear energy. It is intended to attract the highest quality of theoretical and experimental work to ANS, including research on basic phenomena and application to nuclear system design.
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ANS Student Conference 2025
April 3–5, 2025
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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.”
M. M. R. Williams
Nuclear Science and Engineering | Volume 146 | Number 2 | February 2004 | Pages 152-175
Technical Paper | doi.org/10.13182/NSE04-A2400
Articles are hosted by Taylor and Francis Online.
The classic minimum critical mass problem, posed and solved by Goertzel using multigroup diffusion theory, is revisited and reformulated in terms of the two-group transport equation with isotropic scattering. A new variational principle is constructed from which it is possible to derive the conditions necessary for a minimum critical mass. This condition is that the angular thermal flux t([bold]r, [bold]) and a quantity t([bold]r, [bold]) related to the adjoint flux, must obey the constraint[integral]dt([bold]r, [bold])t([bold]r, [bold]) = constant.Contrary to the behavior noted in diffusion theory, this condition does not correspond to a flat thermal flux in the core. This is a major conclusion of the present work.To find the associated solutions, we develop a coupled set of integral equations for the components of the angular flux in the core. We then show that, for weakly absorbing moderators, the lowest order approximation to this set provides an accurate representation of the minimum mass conditions. It also emerges that the flat flux is a very good representation of the true flux. With the above assumptions, the problem reduces to that of solving a Fredholm equation of the first kind for the fuel mass distribution across the core. We solve this equation numerically for the case of an infinitely reflected, infinite slab and compare the results with those from diffusion theory. The transport theory results show one very interesting and important feature, namely, a steep rise in fuel concentration as the boundary is approached which goes to infinity at the boundary. This is in contrast to the diffusion theory result which requires an ad hoc addition of surface delta functions for a solution to exist. Thus we come to the conclusion that the increased surface concentration of fuel is a natural consequence of transport theory but not of diffusion theory. This is the second major conclusion of this work. Detailed numerical results are presented for 235U-graphite and 235U-water mixtures.
