Criticality Analysis of Pu and U accumulations in a Tuff Fracture Network

The objective of this analysis is to evaluate accumulations within the thermally altered tuff surrounding a drift. The evaluation examines accumulation of Uranium minerals (sddyite), Plutonium oxide (Pu2O), and combinations of these materials. A hypothetical model of the tuff is used to provide insight into the factors that affect criticality for this near-field scenario. The factors examined include: the size of the accumulation, the fissile composition of the accumulation, the water of clayey material in the accumulation and the water fraction in the tuff. The solution method is to use the MCNP4A computer program (CSCI:30006 V4A) to calculate k-effective for criticality safety evaluations.