Unavailabilty of containment cooling fans

The Doel 1 NPP is equipped with 4 internal cooling fans to provide for cooling capacity inside the reactor containment after a Design Basis Accident. These fans are operating together with the spray system to reduce pressure and temperature inside the reactor containment in case of loss of energy in this building due to the postulated accident.
During the last outage period, the licensee performed additional verifications (as-found tests) of the tightness of the containment cooling fans motors. These motors should be able to operate under severe environmental conditions (high pressure and temperature) and their tightness is required, according to the original qualification tests, to prevent significant introduction of water and/or steam into the motor casing which could cause failure of the motors.
The leak tightness tests showed that all the motors were not in conformity with the test acceptance criteria. The consequence of this non-conformity is that the Licensee cannot demonstrate the availability of these motors under accident conditions. According to the technical specification requirements, all the containment cooling fans have to be operable while the unit is in normal operation.
Due to the observations made on Doel 1, the Licensee decided to stop Doel 2 unit which has the same components (Doel 1&2 are twin units). The leak tests performed on the fan cooling motors on this last gave the same results as for the Doel 1 unit: none tests of the 4 motors were successful.

Location: DOEL-1
Event date: Thu, 05-10-2006
Nuclear event report
Legenda & explanation