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NRC proposes changes to its rules on nuclear materials
In response to Executive Order 14300, “Ordering the Reform of the Nuclear Regulatory Commission,” the NRC is proposing sweeping changes to its rules governing the use of nuclear materials that are widely used in industry, medicine, and research. The changes would amend NRC regulations for the licensing of nuclear byproduct material, some source material, and some special nuclear material.
As published in the May 18 Federal Register, the NRC is seeking public comment on this proposed rule and draft interim guidance until July 2.
Tuomas Viitanen, Jaakko Leppänen
Nuclear Science and Engineering | Volume 180 | Number 2 | June 2015 | Pages 209-223
Technical Paper | doi.org/10.13182/NSE14-46
Articles are hosted by Taylor and Francis Online.
This paper discusses the generation of temperature majorant cross sections, the type of cross sections required by two separate techniques related to Monte Carlo neutron tracking, namely, the Doppler-broadening rejection correction (DBRC) and target motion sampling (TMS) temperature treatment methods. In the generation of these cross sections, the theoretically infinite range of thermal motion must be artificially limited by applying some sort of a cutoff condition, which affects both the accuracy and the performance of the calculations. In this paper, a revised approach for limiting thermal motion is first introduced, and then, optimal cutoff conditions are determined for both the traditional majorant, commonly used in DBRC implementations and old implementations of the TMS method, and the revised majorant. Using the revised type of temperature majorant cross sections increases the performance of the TMS method slightly, but no practical difference is observed with the DBRC method. It is also discovered that in ordinary reactor physical calculations, the cutoff conditions originally adopted from the SIGMA1 Doppler-broadening code can be significantly relieved without compromising the accuracy of the results. By updating the cutoff conditions for majorant generation, the CPU time requirement of Serpent 2.1.17 is reduced by 8% to 23% in TMS calculations and by 1% to 6% in problems involving DBRC.