Integrity assessment of spent fuel assembly in vertically and obliquely dropping cask

It becomes important to manage adequately spent nuclear fuels (SNFs) for storage away from reactor and/or final disposal as the plant onsite capacity nearly reaches to saturation state. Although the Korean government has enacted relevant regulations and safety measures including several kinds of test for transport cask, a matter of interest should be extended to protect radioactive contents against accidents in conjunction with their future retrievability as well as transportability if necessary. The objective of this study is to demonstrate integrity of typical SNF rods in a developing dual purpose cask under six postulated 9 m free drop scenarios. At first, a series of finite element (FE) analyses of simplified spent fuel assembly (SFA) with external volume and equivalent mass were performed to find out the most severely damaged ones taking into account heavy computational cost. Subsequently, paired FE analyses were also carried out after detailed modeling of the selected SFA with fuel rods arrangement and practical material properties. Finally, structural integrity of the critical SNF rods was evaluated according to the vertical or oblique drop scenarios. The calculated maximum plastic strains at Zircaloy cladding were compared with specific failure criteria dependent on burn-up levels, of which engineering meaning and incorporated conservatism were discussed.