Modeling of SRS Aluminum-clad Spent Nuclear Fuel in Standard DOE Sealed Canisters

Abstract

At the Savannah River Site (SRS), approximately 7 MTHM of aluminum-clad spent nuclear fuel is currently in wet storage at L-Basin. Current baseline planning is to process the spent nuclear fuel at H-Canyon. A potential alternative to H-Canyon processing is to dry the fuel and package in a road ready configuration using a multi-purpose canister, such as the DOE standard canister. To understand the potential for gas generation in the canisters, first the thermal and dose rate profiles need to be resolved. A computational fluid dynamics model is built to resolve the 50-year trend for the thermal profile, and MCNP is used to resolve the decay heat and surface dose rate of the fuel. This report will focus on a few fuel types, which should bound all other fuel stored at SRS. These consist of the reference fuel assembly, the MURR fuel and the HFIR fuel. These bound a hypothetical maximum scenario for MTR box fuel, a maximum for decay heat in an assembly, and a maximum for the aluminum surface area, respectively. The geometry for the packages was created from DOE specifications for storage of each of the fuels. As long as the minimum time from reactor discharge to sealed storage is 3 years, then the highest temperatures which occur within the sealed canisters do not exceed 100 C for all scenarios considered here. If the minimum time from reactor discharge to sealed storage is 10 years, the maximum temperature does not exceed 50 C for all the scenarios considered. In the geometry considered, while the HFIR fuel has a large surface area, the packaging configuration leaves large void areas, such that the aluminum surface to free volume ratio is about 30% less than an ATR or MURR packaging configuration. Due to the highest surface area to volume ratio for a loaded DOE standard canister, and a high maximum temperature for the aluminum surface, the MURR loaded DOE standard canister should provide a bounding case for all aluminum-clad fuel currently stored at SRS.

Technical basis for extended dry storage of aluminum-clad spent nuclear fuel

“…This includes sealed and vented dry storage configurations of ATR and other ASNF types within canisters with different backfill gases, such as He. 23,24,25,26,27,28,29 All work completed to close this knowledge gap supports the conclusion that extended ASNF dry storage is both safe and viable.…”

Technical Basis for Extended Dry Storage of Aluminum-Clad Spent Nuclear Fuel

“…This includes sealed and vented dry storage configurations of ATR and other ASNF types within canisters with different backfill gases, such as He. 23,24,25,26,27,28,29 All work completed to close this knowledge gap supports the conclusion that extended ASNF dry storage is both safe and viable.…”