Safety evaluation of an extended refilling mode operation after the permanent shutdown of a BWR/4 reactor

According to the steady state analysis of the extended storage pool, the early transition phase with RHR system cooling to the core will be three days, to assure the maximum water temperature in the core below the technical specification limits. Moreover, an assessment of a LBLOCA with rupture at recirculation line was performed by RELAP5 model. It was indicated that the existing makeup system cannot provide effective makeup coolant to the reactor core, unless the makeup coolant could be directed into the core shroud. It was also demonstrated by RELAP5 simulation that only the core spray can provide effective cooling to the reactor core, even under the worst recirculation line break scenario.