Fuel rod behaviour in normal operation, in case of malfunctions and during long-term storage

The RS1518 project aims to develop methods for the analysis of the fuel rod behaviour, based on the findings of the precursor project RS1193. The project is divided into the work packages for behaviour with reactivity initiated accidents (RIA), loss of coolant accidents (LOCA), behaviour during load follow operation, and behaviour during long-term storage. The latter applies to the interim storage of spent nuclear fuel after reactor operation and before a possible geological disposal or alternative treatment. In the context of an OECD-NEA RIA benchmark, the fuel rod code TESPA-ROD was compared with other simulation codes on the subject of reactivity initiated accidents. The resulting code predictions were subjected to an uncertainty and sensitivity analysis. The partial large uncertainties in the results show the necessity for the continuative validation on experimental data. The QUENCH-LOCA tests performed by KIT investigating the hydrogen up-take in the ballooned cladding during LOCA have been utilized for modelling the hydrogen up-take in the TESPA-ROD code. In addition to that, a model for fuel relocation within the strained cladding has been developed for the fuel rod code TESPA-ROD. Studsvik-SCIP-HRX experiments on the cladding creep behaviour have been analysed and specific creep models have been deduced from that. These new creep models provide the basis for the understanding of mechanical phenomena in pellet/cladding (mechanical) interaction (PCI / PCMI) which might occur during load follow operation. The applicability of fuel rod code TESPA-ROD has been extended to perform analyses for the fuel rod behaviour of irradiated fuel during long-term storage. In this case the long-term storage covers a period of more than 100 years. It is shown by means of multiple code predictions under varying boundary conditions that the TESPA-ROD code can be applied in safety analyses. Compliance with fuel rod criteria, such as permanent cladding strain and circumferential stress in the cladding can be assessed by the TESPA-ROD code.