Improvements of interfacial friction and heat transfer models for rectangular narrow channel reflood simulation based on RELAP5

Abstract

Abstract Plate fuel assembly is widely used in reactor cores due to benefits of the narrow rectangular channels. Compared with rod assembly, the heat transfer area and power density can be increased in narrow rectangular channel, where little researches on post-CHF thermal-hydraulic characteristics have been done. Once the loss of coolant accident happens, post-CHF thermal-hydraulic characteristics are important for accident mitigation. This paper mainly evaluates the corresponding reflood models in RELAP5/MOD3 code. Combined with the post-CHF thermal-hydraulic characteristics in the narrow channel, interfacial friction model and post-CHF heat transfer models are modified. According to the comparison results with Saxena reflood experiments, conclusions can be obtained that the original RELAP5/MOD3 code overestimates quench front velocity and heat transfer in the film boiling region. The results from the code with new models agree better with the experimental data.