Thermal Analysis of Vertical Dry Storage Cask for Nuclear Spent Fuel in Off-Normal Conditions

One of the key aspects for safety assessment of spent fuel dry storage systems is evaluation of the temperature profile for spent fuel in various storage conditions. In this effort, a three-dimensional model of a vertical dry storage HI‑STORM 190 UA system for VVER-1000 fuel is developed for ANSYS CFX code. This model is then used for the analysis of spent fuel thermal state in normal conditions and in a hypothetical case of a loss of the fuel canister integrity. Canister depressurization with helium leakage and its substitution with air lead to degradation of heat removal and increase of spent nuclear fuel temperature. 
The results presented in this article demonstrate that the maximum cladding temperature of spent fuel does not exceed the design limit in normal storage conditions. In the case of loss of the fuel canister integrity, the maximum cladding temperature exceeds this design limit for normal storage conditions, but remains below the limit for short-term off-normal conditions. The results also demonstrate that loss of the fuel canister integrity leads to insignificant change in vents outlet temperature and cannot be reliably identified by temperature monitoring according to the existing procedures.