The effect of storage conditions and computer model simplification on the thermal state of the RBMK-1500M2 cask

Interim storage of spent nuclear fuel is a very important part of the overall nuclear power generation cycle. At Ignalina NPP, spent nuclear fuel is stored in interim storage facilities in specially designed casks before being transferred to a geological repository. The internal structure of spent nuclear fuel casks and the processes involved are quite complex. Therefore, simplifying and optimizing simulations for evaluating decay heat removal from the cask is worthwhile. In this paper, the effect of computer model simplifications on the thermal characteristics of the CONSTOR RBMK-1500/M2 cask stored in building-type and open-type storage facilities is presented. The modeling was carried out using the ANSYS Fluent code. The analysis showed a substantial impact of solar insolation. Also, in the case of the homogenization of the SNF load in the basket, higher temperatures are obtained compared with the case when detailed modeling of the internal basket structure is performed. Hence, it was demonstrated that the homogenization model can be used in safety assessment as a conservative approach for the modeling of decay heat removal from the cask.