Modeling of dimensional changes of spent WWER fuel rods during dry storage

The engineering model of anisotropic creep is developed to predict the behavior of WWER fuel rods in dry storage of spent fuel. The model considers several deformation mechanisms, the main one being the dislocation creep. The effects of radiation defects accumulation and its partial annealing during storage, as well as work hardening are taken into account. Based on the available experimental data preliminary verification of the developed model is performed. The model adequately describes the data set used. Conditions of experiments conducted up to date are more severe in temperature and stresses than ones in dry storage. It is shown that in dry storage additional deformation mechanisms play an important role. One such mechanism is the creep induced by temperature cycling that occurs during the experiments. Thermal cycles produce internal stresses caused by thermal expansion anisotropy in α-Zr crystallites. This mechanism makes a significant contribution to the experimentally measured strain at stresses characteristic for spent fuel claddings. Additional experimental research is planned to expand the range of Verification Matrix to the prototype conditions for dry storage and to improve prediction accuracy of the model. (author)