 INES 2 |
DEFECTIVE WELDS IN LOW PRESSURE SAFETY INJECTION SYSTEM |
On Saturday 22 June, during a shutdown of reactor no. 2 for partial inspection and refueling, cracks were observed in the small-diameter branch-pipes in the two low-pressure safety injection system circuits.
The function of this circuit is in the event of an accident (such as a break in the reactor primary cooling system) to introduce borated water into the vessel in order to stop the nuclear reaction and to ensure that there is enough water to cool the core.
In the case in question, the activation of the circuit could have resulted in the cracks (several centimeters long) bursting open and could thus have jeopardized the safety of the reactor. However, a preliminary study seems to indicate that the safety margins used in the circuit calculations would have made it possible to bring the reactor to a safe shutdown state.
As soon as the faults were discovered, checks were carried out on other 1300 MW(e) pressurized water reactors. The first investigations revealed that the Golfech 1, Cattenom 3 and Cattenom 4 units were also affected by this fault but to a lesser degree, since only one circuit was affected at these three reactors and the cracks were smaller.
Inspectors from the nuclear division of the DRIRE Centre will carry out an inspection in connection with the discovery in the next few days.
BASIS FOR RATING: As an identical fault (common mode) was discovered in the two circuits of an important safety system, this anomaly is classified at level 2 on the severity scale.
DIFFICULTIES IN RATING:
Event date: Sat, 22-06-1991
