Three-dimensional numerical research on coupling heat transfer characteristics of PRHR HX under different water levels based on the experimental model

Abstract

The passive residual heat removal system (PRHRs) is an important heat transfer system to ensure the removal of residual heat in non-LOCA conditions occurring in advanced Generation III nuclear reactors. The water level of the In-containment Refueling Water Storage Tank (IRWST) decreases due to long-term water evaporation under accident conditions and the later stages of PRHRs operation. Additionally, the water level also decreases during the water leakage accidents. The reduction of water level contributes to a decrease in the heat transfer area and the passive residual heat removal ability of the core. In order to investigate the coupling heat transfer characteristics of both primary and secondary side in the heat exchanger under different water levels, Three-dimensional numerical simulations of the PRHR HX's operation under different water levels was carried out based on the scaled-down IRWST&PRHR HX experimental model. The fluid flow and heat transfer processes inside and outside the C-type tubes were analyzed in detail. The results indicate that when heat transfer area is reduced by 50%, the overall heat transfer rate is reduced by about 41%, meanwhile the average heat transfer coefficient is about 37.4% higher than that under the full water level condition. It indicates that PRHR HX can maintain high passive residual heat removal capacity even under half water level, which provides an important reference for the design and safe operation of the PRHR HX.