Impacts of MPC thermal limits on cooling storage requirements at the repository

A companion paper investigates the relationship between bounding cases of waste characteristics received and the recently articulated Multi-Purpose Canister (MPC) reference thermal limits in the MPC Design procurement Specifications. That work indicated that benefits appear to accrue to both the Civilian Radioactive Waste Management System (CRWMS) and the utilities if fuel is delivered to the system generally Oldest Fuel First (OFF) with some modifications to handle so-called {open_quote}outlier{close_quote} assemblies with powers at pick up in excess of single assembly shipping limits. Two approaches are examined in that paper to address the outliers. Those two approaches are also used in this analysis, but the measures of effectiveness (MOEs) are extended to include potential storage requirements to cool MPCs to the disposal thermal limit. The first approach, referred to as derating, assumes that assemblies hotter than the single assembly limit could be loaded as long as the total cask power is below the average thermal limit times the cask capacity. This method results in partially full casks and a net increase in cask purchases, loadings, and shipments which in turn increase cost and risk for both the utilities and the CRWMS. The second approach, referred to here as blending, assumes casks couldmore » be licensed to accommodate a mix of assemblies, some above the single assembly limit and some below. Two types of blending were examined: within-year blending and total pool inventory blending. These approaches were analyzed by computing total MPCs required for the OFF case only. Other approaches, such as phasing in the {open_quote}enhanced{close_quote} MPC design later in the system or reducing system throughput rates, were not examined. Results show that the heat mitigating approaches examined reduce the total numbers of MPCs required and alleviate potential cooling storage requirements.« less