Current methods in qualification of CANDU heat transport pumps for operation under loss-of-coolant accident conditions

The Heat Transport (HT) pumps in a CANDU reactor circulate heavy water coolant through the reactor core under all normal operating conditions. For a Loss-of-Coolant-Accident (LOCA) in the heat transport system, depressurization of the system occurs. It is desirable to establish that the HT pumps will continue to operate under two-phase flow conditions resulting from a LOCA for a short duration. Evaluating the operational behaviour of large centrifugal pumps under two-phase flow conditions is complex. Various techniques have been used with different degrees of reliability and associated costs. This paper presents the current methods used for evaluating the post-LOCA operational capability of CANDU HT pumps. Conclusions from the recent research studies suggest the possibility of using the LOCA test data generated by Ontario Hydro for qualification of future CANDU HT pumps. A methodology for such a cost-effective approach is also presented