 INES 1 |
Manual shutdown of Tsuruga Power Station Unit 2 |
Tsuruga Power Station Unit-2 (PWR, rated power 1160 MWe), Japan Atomic Power Company, was operated at the rated power. At 6.05 a.m. on July 12, 1999, the alarm of the fire monitors, installed at the entrance of C loop and D loop compartments inside reactor containment, were initiated. The containment sump level alarm was also initiated, indicating high level increasing rate, and the increase of dust monitor indication inside reactor containment was also recognised. The unit-2 was started to reduce power at 6.24 a.m. on the same day and was shut down manually at 6.48 a.m. on the day.
After the reactor was put into cold shutown condition (about 93 degrees C) at 6.00 p.m., the staff entered into the reactor containment. As a result of inspection at about 7.20 p.m., it was recognized that the reactor coolant was leaking from the insulation portion close to the regenerative heat exchanger of the Chemical and Volume Control System. At 8.16, system isolation was made for the leaking portion, and at 8.29, termination of the leakage was identified. The total amount of the leaked coolant is now estimated as 89 cubic meters. As a result of evaluation, total leakage is concluded as 61 tons based on the coolant volume transferred from the containment sump to the Waste Processing System. The leaked coolant into the reactor containment sump and on to the floor is being transferred to the liquid waste processing system from 10.00 p.m. As a result of inspection of the concerned portion after removing the insulation, about 80 mm length crack was identified on the surface of piping connecting to the regenerative heat exchanger.
Detailed inspections and the cause investigation will be done from now on.
Justification of Rating:
According to the defence in depth criteria of the INES manual, it is evaluated as level 1.
Event date: Mon, 12-07-1999
