System Pressure Effect on System and Core Cooling Behavior during Reflood Phase of PWR LOCA

Abstract

The system pressure is one of the most important parameters for the thermal-hydraulic behavior during the reflood phase of a PWR LOCA. System reflood tests are performed using the Cylindrical Core Test Facility (CCTF) to study the system pressure effect during the reflood with the same ECC water injection method as the actual PWRs. Through the comparisons with the FLECHT SET results, the qualitative differences of the system pressure effect are identified for the downcomer water head, core inlet subcooling and differential pressure through primary loops between two facilities. The differences of the system pressure effect between the FLECHT SET and the CCTF are caused by the differences of the flow area scaling of the broken cold leg and the ECC water injection method. The higher system pressure resulted in the better core cooling in the CCTF tests are observed in the FLECHT SET tests. It was confirmed quantitatively that the predominant factor for the core heat transfer enhancement with the system pressure is the steam density increase with the system pressure. The CCTF results support the assumption that the lower system pressure should give conservative core cooling behavior during the reflood phase of a PWR LOCA.

KEYWORDS:

• heat transfer
• loss of coolant
• pressure dependence
• PWR type reactors
• reactor cooling system
• reactor safety
• reflood
• steam density
• two-phase flow