10 February 2000

Measures to Prevent Reoccurrence of Power Loss (Failure) at the Rokkasho Vitrified Waste Storage Center

Japan Nuclear Fuel Limited

Japan Nuclear Fuel Limited (JNFL) has conducted investigations to determine the cause of the loss (failure) of external power that occurred at the Rokkasho Vitrified Waste Storage Center on January 26, 2000. Based on the results of its investigations, JNFL has decided to implement the following measures to prevent reoccurrence.

Measures to Prevent Reoccurrence of Power Loss (Failure)

(1) Loss of External Power The misoperation was caused by the lack of clarity regarding which procedures needed to be confirmed and the lack of markings clearly distinguishing the current-carrying side and the spare-power side of the operating rope that cuts the electric power system. To prevent future misoperation by workers in the switching of power sources, the procedures manual will be revised, and the current-carrying side of the operating rope will be clearly marked. (Scheduled to be completed by February 10) (2) Interruption of the Collection of Exhaust Samples from the Ventilation Cylinder Monitor The starting program for the sample pump was revised because of some deficiencies in the program for the sample pump which had been designed to restart with the starting of the spare-power diesel generator. (Completed on January 27) (3) Fluctuations in Differential Pressure between the Controlled Area and the Examination Room The air supply and exhaust air became unbalanced because of a defect in the temperature sensor which controls the starting and stopping of air supply and exhaust. For this reason, the temperature sensor in question in the electric equipment room was replaced. (Completed on February 9) (4) Period until the Repair of the Ventilating Equipment in the Controlled Area The procedures manual for operations at the time of loss of external power will be revised, and the manual will clearly forbid the start up and operation of equipment that is not designated to be feed power from the spare-power diesel generator. (Scheduled to be completed by February 10)