Publications

Fissile mass and concentration criteria for criticality in geologic media near bedded salt repository

Rechard, Robert P.; Sanchez, Lawrence C.; McDaniel, Patrick K.; Hunt, Jacob; Broadous, Gabriella

This paper describes the fissile mass and concentration necessary for a critical event to occur outside containers disposed in a bedded salt repository. The criticality limits are based on modeling mixtures of water, salt, dolomite, concrete, rust, and fissile material using a neutron/photon transport computational code. Several idealized depositional configurations of fissile material in the host rock are analyzed: homogeneous spheres and heterogeneous arrangements of plate fractures in regular arrays. Deposition of large masses and concentrations are required for criticality to occur for low enriched 235U enrichment. Homogeneous mixtures with deposition in all the porosity are more reactive at high enrichments of 235U and 239Pu. However, unlike typical engineered systems, heterogeneous configurations can be more reactive than homogeneous systems at high enrichment when deposition occurs in only a portion of the porosity and the total porosity is small, because the relationship between the porosity of the fractures and matrix also strongly influences the results.