Fuel integrity evaluation method for BWR-6 plant Kuosheng during ATWS events

Anticipated Transients without Scram (ATWS) are evaluated to demonstrate that during ATWS the fuel’s integrity prevents fission product release, and that the safety features the BWR-6 plant is equipped with mitigate the ATWS event. For analyzing this scenario, a RETRAN-3D system model and hot channel model of Kuosheng NPP have been developed. From all possible events those are analyzed where the main steam isolation valves close (MSIVC) when the reactor is operating at rated power conditions. For cases with low core flows this results in higher peak cladding temperatures and thicker oxidation thicknesses. All results confirm the ATWS acceptance criteria. For sensitivity cases, increasing the boron concentration of standby liquid control system (SLCS) or injecting boron of SLCS earlier were investigated. The results show, that these measures cannot decrease the PCT value immediately, but can shorten the period of peak cladding temperature over 850 °C which results in smaller oxidation thickness.