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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.
R. N. Hill, K. O. Ott, J. D. Rhodes
Nuclear Science and Engineering | Volume 103 | Number 1 | September 1989 | Pages 25-36
Technical Paper | doi.org/10.13182/NSE89-A23657
Articles are hosted by Taylor and Francis Online.
Analytical exploratory investigations indicate that transition effects such as streaming cause a considerable spatial variation in the neutron spectra across resonances; streaming leads to opposite effects in the forward and backward directions. The neglect of this coupled spatial/angular variation of the transitory resonance spectra is an approximation that is common to all current group constant generation methodologies. This paper aims at an accurate description of the spatial/angular coupling of the neutron flux across isolated resonances. It appears to be necessary to differentiate between forward- and backward-directed neutron flux components or even to consider components in narrower angular cones. The effects are illustrated for an isolated actinide resonance in a simplified fast reactor blanket problem. The resonance spectra of the directional flux components φ+ and φ‾, and even more so the 90-deg cone components, are shown to deviate significantly from the infinite medium approximation, and the differences increase with penetration. The changes in φ+ lead to a decreasing scattering group constant that enhances neutron transmission; the changes in φ‾ lead to an increasing group constant inhibiting backward scattering. Therefore, the changes in the forward- and backward-directed spectra both lead to increased neutron transmission. Conversely, the flux (φ = φ + + φ‾) is shown to agree closely with the infinite medium approximation both in the analytical formulas and in the numerical solution. The directional effects cancel in the summation. Therefore, flux-weighted (“diffusion theory”) group constants cannot accurately describe the transmission problem, even using transport theory, as the use of flux weighting eliminates the significant directional effects. The forward- and backward-directed flux components are used as weighting spectra to illustrate the group constant changes for a single resonance. Results indicate that these changes have a magnitude that can likely account for calculational underpredictions observed in fast reactor blanket regions.
