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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.
Mark S. Jarzemba, James Weldy, English Pearcy
Nuclear Science and Engineering | Volume 131 | Number 2 | February 1999 | Pages 275-281
Technical Paper | doi.org/10.13182/NSE131-275
Articles are hosted by Taylor and Francis Online.
Two subcritical assemblies (consisting of a subcritical reactor plus a neutron emitter such as 252Cf) designed for conducting neutron activation analyses in the field are described. The size of the assemblies has been minimized (compared to conventional, graphite-moderated assemblies) to allow for field portability. Although less powerful than using a research reactor as the source of neutrons, these assemblies will provide an adequate source of neutrons for detecting gold concentrations in rock or soil samples down to the limits of economic importance. Using a field-portable source of neutrons eliminates the need for shipping samples back to the reactor for analysis, which may be important for reasons of sample security and measurement turnaround time. The two subcritical assemblies are composed of natural uranium metal as the multiplying material and high-density polyethylene as the moderator, and they have keff approximately equal to 0.8 for the smaller assembly (~692-kg assembly mass) and 0.9 for the larger assembly (~3059-kg assembly mass). The larger assembly was found to be more desirable from a neutronics standpoint; however, it may be too massive to maintain field portability. It was found that the optimal location for the irradiation facility (a 4.0-cm-high, 2.0-cm-diam right cylinder) in the subcritical assemblies is the grid location as close to the neutron emitter location as possible. It was also found that the total, epithermal plus thermal (i.e., neutron energy <0.5 eV), and thermal (i.e., neutron energy <0.05 eV) volume-averaged neutron fluxes were as follows (assuming a neutron emitter source strength of 109 n/s): 1.72 × 108, 4.47 × 107, and 2.15 × 107 cm-2s-1 for the smaller assembly, and 3.43 × 108, 9.09 × 107, and 4.37 × 107 cm-2s-1 for the larger assembly. Although the purpose for which the assembly was designed was for conducting neutron activation analyses for gold, the assemblies should also work equally well for analyzing sample compositions of other elements at both the bulk and trace levels.
