Simulation of Zircaloy and SiC cladding thermal performance of a nuclear fuel rod subassembly

Abstract A thermal-hydraulic analysis of a nuclear fuel rod subassembly of a Pressurized Water Reactor (PWR) has been performed during a Loss of Flow Accident (LOFA). Two different cladding materials are studied in this exercise namely, (a) conventional Zircaloy (Zr) and (b) a Silicon Carbide (SiC) cladding concept approach using monolithic SiC and SiC composite two-layer structure. The simulation is carried out by using USNRC licensed and AERB approved RELAP5/MOD3.4 code. A short-time problem is analyzed, neglecting the burnup change and irradiation effects. A transition into film boiling is observed in the upper part of the rod during LOFA, causing the convective heat transfer coefficient to decrease. The peak cladding temperatures and the Critical Heat Flux Ratio (CHFR) values of the two cladding materials are compared. From a safety perspective, the use of SiC is considered as it will be able to maintain performance during the operational transients.