Thermomechanical and radiological investigations of storage casks for radioactive spent fuel assemblies

In this research, the Monte Carlo particle transport method and COMSOL Multiphysics were utilized to simulate and analyze the TK-13 cask, which contains spent fuel assemblies of the WWER-1000 reactor. Initially, the cask was modeled as being filled with water, and its criticality was assessed by evaluating the effective multiplication factor (Keff) while considering various neutron shielding materials, including polyethylene, borated polyethylene, ethylene glycol, and water solutions. The Keff value was calculated by varying the boron percentage in the holding basket of spent fuel assemblies and adjusting the pitch between these assemblies. Additionally, the total neutron and gamma dose rates on the cask's outer wall were measured. A thick steel wall, 34 cm in thickness, was modeled around the spent fuel assemblies, and a concrete wall was also considered, with total dose rates calculated for both cases. The uncertainty in these measurements was also quantified. The cask was further simulated in COMSOL Multiphysics to evaluate thermal and mechanical parameters. Thermal analysis was conducted in both steady and unsteady states; for steady-state analysis, the minimum and maximum fuel burnup scenarios were examined, along with the effects of fins on the outer wall. In the unsteady thermal analysis, temperature variations at different points within the cask and their distribution over a hundred-year period were investigated. The mechanical analysis focused on Von Mises stress and displacement values at various locations within the cask. Finally, the results were compared with findings from other studies, leading to comprehensive conclusions.