Thermal-Hydraulic Safety Assessment in Advanced Boiling Water Reactors due to Fuel Failure and Loss of Offsite Power

This work presents the safety assessment of thermal-hydraulic parameters in Advance Boiling Water Reactor (ABWR) due to fuel failure at full power concurrently with loss of offsite power transient. Overall thermal-hydraulic of ABWR with various control passive safety systems, trip, accident progression, actuation logics were calculated with system ASYST thermal-hydraulic program. No operator’s interference was involved during simulation. This study was carried out in reference to the main safety margins of the fuel surface temperature, primary coolant flow-rates and primary pressure. Following the postulated events, the accident progression and changes in pressure, mass flow rates, fuel clad temperature and the responses of safety emergence core cooling systems were investigated. The results showed that actuation of passive safety systems in the ABWR enhanced accident mitigation. Primary coolant flow-rates and pressure in the pressure vessel changes did not compromise with the integrity of the reactor. This affirms the inherent concepts and principles of defence-in-depth within the design of ABWR. The results provide confidence in the inherent robustness of the ABWR design with respect to fuel failure at full power concurrently with a full off-site power loss in the validity of a two-tier calculation method. This could be useful in, probabilistic safety assessment, severe accident management guidelines and public acceptance for the ABWR.