Applicability Review of Safety Function for Kori NPP Unit 1 after shutdown permanently

Whether to maintain the safety functions required for safety related structures, systems and components has become an important current issue. This is due to the change in the operating condition of the plant where all fuel is permanently unloaded from the core to Spent Fuel Pool (SFP) with the unit permanently shutdown. In this paper, the aim is to perform accident analysis for permanent shutdown of the Kori unit 1 and based on the results, to review if the safety functions would require to be applied to structures, systems and components (SSC) classified as safety class so that it could be used for exemption of design requirements such as single failure criterion and amendment of documents requiring submission for operating license change. The fuel handling accident (FHA) analysis showed that after 60 days from permanent shutdown, radiation dose for general public are reduced well below allowable limits even without placing heating ventilating and air conditioning system (charcoal filter) in service. This means that exceeding offsite dose limits is of no concern. This means that Kori unit 1 may maintain the safety functions until 60 days after permanently defueled condition where fuel is stored in SFP and after 60 days, these safety functions may not need be implemented. This brings changes in complying with design requirements including single failure criteria. Therefore, according to this accident analysis results, operating license change documents were revised and submitted to maintain one diesel generator for backup power supply and discard operating alternate alternating current diesel generators (AAC D/G).