ANALYSIS OF OPERATOR ACTIONS DURING THE ACCIDENT CAUSED BY TOTAL LOSSOF SECONDARY HEAT SINK

The accident with total loss of secondary heat sink was analyzed for t he Krsko nuclear power plant using the RELAP5/MOD2 computer code and c onsidering the emergency operating procedures foreseen by operator act ions. Particular attention was given to the phenomenological descripti on of thermal-hydraulic processes which may take place in the reactor coolant system during the accident. The investigation aimed to evaluat e the minimal success criteria for various availabilities of plant saf ety systems and operator response times. The longest allowed operator response time for successful accident management was shown to be stron gly dependent on the initial event. Among potential initial events, tw o secondary side originating events were demonstrated to be the bounda ry cases, the turbine isolation results in the longest allowed operato r response time and the loss of main feedwater in the shortest allowed operator response time.