The Monitored Geologic Repository (MGR) Waste Package Operations of the Civilian Radioactive Waste Management System Management & Operating (CRWMS M&O) contractor performed calculations to provide input to the design of a waste package (WP). This document analyzes the degradation processes of two types of pressurized water reactor (PWR) spent nuclear fuel (SNF): • Fuel fabricated from low enriched uranium oxide, which has been used, or will ~ used, in commercial nuclear power plants.

Expanding interest in nuclear power and advanced fuel cycles indicate that use of mixed-oxide (MOX) fuel in the current and new U.S. reactor fleet could become an option for utilities in the coming decades. In light of this renewed interest, EPRI has reviewed the substantial knowledge base on MOX fuel irradiation in light water reactors (LWRs). The goal was to evaluate the technical feasibility of MOX fuel use in the U.S. reactor fleet for both existing and advanced LWR designs (Generation III/III+).

The objective of this analysis is to evaluate accumulations within the thermally altered tuff surrounding a drift. The evaluation examines accumulation of uranium minerals (soddyite), plutonium oxide (Pu01), 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 or clayey material fraction in the accumulation and the water fraction in the tuff