Preliminary hydrologic release scenarios for a candidate repository site in the Columbia River basalts

The National Waste Terminal Storage program is examining a number of different rock types for possible construction of a repository for the storage of radioactive waste. One of the geologic settings being considered is the basalt underlying the Hanford Site of southcentral Washington. The Basalt Waste Isolation Project (BWIP) of Rockwell Hanford Operations is responsible for this feasibility study. As part of this effort, the BWIP is undertaking a consequence analysis of disruptive events that could affect the siting of a nuclear waste repository. Preliminary to a full-consequence analysis, a scenario analysis was first performed to select and rank some of the potentially important disruptive events or processes. In addition to the no-disruptive base case, four scenarios were selected using the expert opinion approach and expected of perceived risk as selection criteria. The geologic and hydrologic conditions associated with each scenario were estimated using available information. The four disruptive scenarios considered were ranked in order of decreasing significance: fault near or through the nuclear waste repository; shaft seal degradation or failure; microearthquake swarm near the repository; and magmatic intrusion