Review and analysis for events of damage of electric circuits for safe shutdown in postulated fires at PWR power plants and countermeasures for preventing loss of inventory water caused by malfunction of valves

The United States Nuclear Regulatory Commission (NRC) has been collecting reports on events concerning postulated fires from the viewpoint of fire protection for nuclear power plants. First of all, we reviewed these reports on the US nuclear power plants and analyzed (1) location of a fire, (2) part where the fire occurred and (3) the cause of the fire. The results revealed that the postulated fires had often occurred in areas dense with cables, such as central control rooms and cable connecting rooms, and the events caused by ground faults and short circuits resulting from cable fires had been predominant. Then, a comparison was made between PWRs in the United States and those in Japan in terms of the items and details of analysis on fire-caused damage of the electric circuits as described above. The comparison revealed that ''the event of loss of inventory water resulting from malfunction of valves caused by a fire'' was given consideration at the PWRs in the United States but not for those in Japan. Accordingly, countermeasures against this event were proposed. (author)