THERMAL PERFORMANCE SENSITIVITY STUDIES IN SUPPORT OF MATERIAL MODELING FOR EXTENDED STORAGE OF USED NUCLEAR FUEL

The work reported here is an investigation of the sensitivity of component temperatures in a specific storage system, including fuel cladding temperatures, in response to modeling assumptions that differ from design-basis, including age-related changes that could degrade the thermal behavior of the system. Preliminary evaluations of representative horizontal and vertical storage systems at design basis conditions provides general insight into the expected behavior of storage systems over extended periods of time. The sensitivity analyses were performed using the detailed computational fluid dynamics (CFD) model of a horizontal storage module developed for the inspections performed at the Calvert Cliffs Nuclear Power Station’s Independent Spent Fuel Storage Installation (ISFSI) in June 2012.
This storage module (designated HSM15) is a site-specific variant of the standard NUHOMS® module, and contains a 24P dry shielded canister (DSC) loaded with twenty-four CE 14x14 spent fuel assemblies. The total decay heat load for the DSC in HSM15 was 10.58 kW at the time of loading (November 1996), after the fuel had spent approximately 12 years in wet storage. At the time of inspection (June 2012), after approximately16 years in dry storage, the total decay heat in the canister was calculated to be 7.58 kW. For the sensitivity analyses, the decay heat load for this fuel was projected to 300 years, and evaluations were performed for 6 kW, 4 kW, and 2 kW, corresponding to fuel approximately 50 years, 100 years, and 300 years old, respectively.