<p>A large break Loss of Coolant Accident (LOCA) is one of the design basis accidents in the safety analyses of a pressurized light water reactor (PWR). Generally, there are four phases under LOCA conditions, i.e., blowdown, refill, reflood and long-term cooling phases. In particular, the reflood phase is an important phase to remove the core residual heat and ensure the core safety. However, the existence of spacer grids may disturb the flow of subcooled water and enhance the convective heat transfer in the region downstream of the fuel bundles during the reflood phase, thereby reducing the peak cladding temperatures (PCTs) and the risk of core melting. Currently, the system analysis code LOCUST has been independently developed in China, which is mainly used for the reactor safety analysis. In order to evaluate the ability of the code to simulate the phenomenon of reflood heat transfer, it is necessary to conduct benchmark study of the Rod Bundle Heat Transfer (RBHT) experiment for the effect of spacer grids on reflood heat transfer with LOCUST code.</p><p>In this study, the system thermal-hydraulic code LOCUST is applied to simulate reflood heat transfer experiments conducted in the RBHT facility, and the effect of spacer grids are considered. The calculation results of LOCUST are compared with experimental data and the calculations of RELAP5. The results show that both LOCUST and RELAP5 are capable of predicting the reflood behaviors at a satisfactory level. Besides, the calculations of cladding temperature and heat transfer coefficient are generally in good agreement with experimental data. When spacer grids are introduced, PCTs calculated by RELAP5 and LOCUST are 1178K and 1182K, respectively. However, the calculations without spacer girds are 1184K and 1187K, respectively. The comparison reveals that a decrease of around 5K in the PCTs occurs due to spacer grids.</p>

Benchmark Study of RBHT Experiment for the Effect of Spacer Grids on Reflood Heat Transfer With LOCUST Code

Paper Proceedings: https://asmedigitalcollection.asme.org/ICONE/ICONE28/volume/85246

2021 28th International Conference on Nuclear Engineering (ICONE28)

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