Transition from EOP to SAMG at Wolsong NPPs

Emergency Operating Procedures (EOPs) are provided for operators to respond properly when accident occurs in nuclear power plants. EOP does not cover severe accident which may cause core damage or core melt. It is trend to develop Severe Accident Management Guidance(SAMG) which gives guidance to staffs in technical support center (TSC) and operators in the main control room to control and make plant stable when severe accident is in progress. If operators fail to control and to make plant stable state in accordance with EOPs and accident progresses to severe accident, TSC staffs decide to stop use of EOPs and start use of SAMG. Core exit temperature is used to determine occurrence of severe accident in Light Water Reactors. The core of CANDU reactor consists of 380 fuel channels and each channel is submerged in moderator which is heavy water. Moderator can remove decay heat and does not lead to severe core damage even though coolant is not injected in the fuel channel by emergency core cooling system. Previous paper proposed that it is believed severe accident has occurred if fuel channels are not covered by moderator. Pipe break in the moderator system may reduce moderator level even though the cooling is established. So in addition to the moderator level, new parameter is added to determine the occurrence of severe accident