The accumulation and flow resistance characteristics of LOCA-generated debris in different PWR fuel assemblies

Abstract

The debris generated by loss-of-coolant accidents (LOCA) in a pressurized water reactor (PWR) might pass through sump strainers and flow into the reactor core. That debris can potentially plug the flow channel in fuel assemblies (FAs) and adhere to the fuel rods, thereby retarding the core cooling. To investigate this safety issue, this work initiated a prototypical FA testing program under post-LOCA conditions in three different PWR FAs, QS300, AP1000 and CAP1400. The accumulation characteristics of debris in three FAs and the corresponding flow resistance were analyzed. Experimental results showed that the debris primarily distributed in the lower half of FA, especially in the bottom nozzle (BN). The BN of CAP1400 FA exhibited excellent debris-filtering capacity due to its optimized structure. The fiberglass debris is most supposed to be restricted because a dense and uniform debris bed could form with a small quantity of fiberglass and cause significant flow resistance by filtering fine chemicals.