A Thermal Analysis of TN-24P Dry Storage Cask System

The capability of on-site storage of used nuclear fuels (UNFs) generated in the domestic nuclear power plants is project to reach the limit from the year of 2024. It seems necessary to utilize dry storage casks for the interim storage of used nuclear fuels at near future. In this work, the temperature distributions in the UNFs in the TN-24P vertical cask were obtained by conjugate heat transfer simulations. The COMSOL MULTIPHYSICS 5.2a computer program was used to evaluate the conjugate heat transfer simulations coupling with three types of heat transfer by solids and fluids and the natural convection fluid flow. Three cases of the simulations under helium, nitrogen gases and vacuum condition were performed to get the temperature distributions of the UNFs in the cask. From the results, the following conclusions are drawn. Comparison of the simulation results and measured values from the tests for the three conditions showed good agreement within 10% in the active region. The temperature profile for the vacuum backfill condition without any natural convection was significantly higher than the other backfill condition. The temperature profile for the two backfill gases with natural convection were skewed toward the upper one half of the active fuel length. The peak temperature and its location for the nitrogen natural convection was higher than that for the helium natural convection. Because the Nusselt number for the nitrogen backfill gas was about four times higher than that for the helium backfill gas. In other words, the nitrogen backfill gas occurred more natural connectively than helium gas or the helium backfill gas occurred more natural conducively than nitrogen gas.