Possibility of experimental validation of criticality safety methodology in support of underground fuel storage efforts

摘要

Critical systems which might be formed in geologic repositories as a result of long-term degradation of the storage media, leaching of plutonium from the storage media, and the redistribution of low concentrations of plutonium into underground sand layers or lenses can be characterized by positive reactivity feedback. Formation of such a systems can not be excluded when considering the burial of high enriched uranium or plutonium contaminated wastes or spent nuclear fuels. Although the probability of formation of a critical systems under such conditions is very low, the reliable prediction of neutron multiplication properties appears to be of great interest from a criticality safety view point. At the present time, all estimations of criticality are based only on evaluated neutron data because critical experiments are not available for large systems containing small quantities plutonium distributed throughout a typically encountered matrix material such as silicon dioxide. The possibility of providing such an experiment using the large Russian critical assemblies, BFS-1 or BFS-2, is considered. It is shown that critical systems containing small amounts of hydrogenous material (polyethylene) with positive reactivity feedback can by modeled in the BFS Facility.