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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.”
Enzo Curti, Matthias Krack, Daniel Grolimund (Paul Scherrer Inst), Sergey V. Churakov (Paul Scherrer Inst/Univ of Bern)
Proceedings | 16th International High-Level Radioactive Waste Management Conference (IHLRWM 2017) | Charlotte, NC, April 9-13, 2017 | Pages 281-285
The long-lived nuclide 79Se plays a key role in safety assessments for underground radioactive waste repositories. In general, Se is assumed to diffuse out of the fuel grains and to migrate toward the periphery of fuel pellets due to the high thermal gradient during LWR reactor operation, similarly to the volatile elements I and Cs. According to this model, a significant part of the 79Se inventory in spent fuel would be readily accessible to leaching after water ingress in the repository. However, contrary to these expectations, leach experiments did not show measurable Se release after exposing spent UO2 fuel samples to aqueous solutions during up to one year.
In order to explain this result, X-ray absorption near edge structure (XANES) spectra were measured on microsamples of high-burnup UO2 spent fuel from two light water reactors. The results indicate that Se occurs in the fuel as sparingly soluble, almost immobile Se(-II) ion (selenide). The occurrence of soluble oxidized forms of Se could be ruled out. Theoretical XANES calculations proved to be consistent with Se occupying oxygen sites in the UO2 crystal structure.
From these results we conclude that the release of 79Se from UO2 spent fuel in an underground repository will be controlled by the slow dissolution of the fuel matrix and not by early short-term release. Our spectroscopic data thus explain why dissolved Se was not detected in the leach experiments. Moreover, they are essential to reliably define critical source term parameters, specifically the "Instant Release Fraction" (IRF), in performance assessment calculations.