Heat transfer analysis and assessment of trans-critical pressure transient

For SCWR, the occurrence of pressure transient across critical point (22.064MPa) is possible during startup, shutdown and also loss of coolant accident. Under subcritical condition, CHF decreases rapidly as the pressure tends toward the critical point, which would even lead to severe wall temperature rise. Hence, the study of trans-critical processes is of crucial importance to safety analysis of SCWR. In this study, the validation work for trans-critical pressure transient is launched based on transient experiment on SWAMUP in SJTU and ATHLET-SC, a system code modified in SJTU. As demonstrated, ATHLET-SC could calculate the trans-critical process successfully. The wall temperature could be predicted well at supercritical pressure. But for subcritical condition, the wall temperature increase and rewetting phenomena are not presented as expected. Therefore, heat transfer mechanism is analyzed during the trans-critical process and new heat transfer methodology is applied to ATHLET-SC. (author)