Thermal modeling and performance analysis of interim dry storage and geologic disposal facilities for spent nuclear fuel

Thermal models are constructed and analyses are performed of aluminum-based spent nuclear fuel (Al-SNF) in interim dry storage and geologic disposal configurations. Two models are developed referred to as the interim storage model and the codisposal waste package (WP) model. Time-dependent source terms of Al-SNF forms and the defense high-level waste (DHLW) canisters are also developed for thermal performance analysis of the geologic codisposal WP. The interim storage model is a three-dimensional conduction-convection conjugate model to investigate the natural convection cooling of a sealed dry storage canister with vertical orientation in a dry storage vault. The analysis is made for various decay heat sources (Equivalent to 25 to 35 kW/m(3)) using various boundary conditions around the canister wall and,with backfilled nitrogen or helium gas. Based on the data obtained from the Savannah River Site experimental work and available from the literature, an improved dimensionless correlation for the external heat transfer of the canister by the airflow crossing normal to the staggered tubes is developed. The codisposal WP model considers heat transfer driven by conduction and convection processes combined with radiation for the thermal performance study of an enclosed WP containing one Al-SNF canister and five DHLW glass canisters. Two-dimensional analysis for a representative cross-sectional area of the codisposal WP is performed because each component has a lar ge aspect ratio of package length to diameter and the package is laid down horizontally in a drift tunnel repository. The results showed that the codisposal disposition options for the helium- and air-filled WPs satisfied the present waste acceptance criteria for the WP design under the reference conditions.