Comparative analysis of RIA and LOCA with and without fuel rod behavior modeling in THEATRe code

Fuel rod behavior during accidents and transients is one of the important safety issues especially under Design Base Accidents (DBA) such as LOCA and RIA. Not only accidents and transients have their impact on fuel behavior but fuel behavior also affects the accident progression. In this study, a comparative analysis has been performed. In that, LOCA and RIA are analyzed with and without fuel rod behavior modeling in THEATRe code. The code is modified by adding fuel rod behavior models. The AP1000 reactor is considered as a reference reactor for this analysis which uses typical cylindrical UO2 fuel rod. Three RIA cases and initial phases of small break LOCA are simulated. The RIA cases include the reactivity addition at 100%, 50% and 1% of nominal reactor power. The results indicate that the inclusion of fuel rod behavior models in the modified THEATRe code affects the temperature distribution in the fuel rod and some nuclear plant conditions both for steady state and accidents conditions as compare to the original code. The analysis performed in this study is conducted for un-irradiated fuel. However, the effects of fuel behavior during steady state, transients and accidents conditions would be more pronounced in case of burned fuel. Therefore, for more consistent safety analysis, fuel behavior modeling is important as far as all relevant phenomena are precisely addressed and modeled.