Development of PHWR (CANDU-6) safety analysis methodology using parallel coupling method with thermal hydraulics/reactor physics computer codes

Abstract

A new safety analysis method for a moderator system failure event in a PHWR (CANDU-6) has been developed using a coupling analysis method with the thermal hydraulic code - CATHENA and reactor physics code - RFSP-IST. This sophisticated method can replace the non-qualified and legacy method with the MODSTBOIL and SMOKIN-G2 for the thermal hydraulics and reactor physics, respectively. The CATHENA thermal hydraulics model for the moderator system can simulate the thermal hydraulic behaviors of all the moderator systems, such as the calandria tank, head tank, moderator circulating circuit and cover gas circulating circuit, and therefore can predict the thermal hydraulic properties of the moderator, such as the moderator density, temperature and water level in the calandria tank, as moderator system failures progress. Further, these calculated moderator thermal hydraulic properties are provided to the 3-Dimensional neutron kinetics solution module - CERBRRS module of RFSP-IST as input data, which can predict a change in the reactor power and provide the calculated reactor power to the CATHENA in turn. These coupling analysis are performed at every time step using parallel coupling method of both codes. The safety analysis results using this newly developed method reveal that the reactor operation enters into the self-shutdown mode without any engineering safety system and/or human interventions for the postulated moderator system failure events (Loss of Moderator Heat Sink and Loss of Moderator Inventory).