Emergency water/reheater drains distribution header damage inside the steam generators

The reactor was shutdown on 96-09-29 to inspect the secondary side of Boiler #3 to determine the cause of level disturbance anomalies. Entry to Boiler #3 into the area of the Emergency Water Supply/Reheater Drains Distribution Header was made on 96-10-04 as part of the boiler fitness for service assessment. During the inspection, it was discovered that the header had severe erosion/corrosion damage. Through wall holes in the header were found at the tee connection, and the sleeve connection at the shroud was displaced and damaged. Consequently, a decision was made to inspect the headers in all boilers. Similar damage was found in each boiler. The headers in all boilers were removed and replaced with an erosion/corrosion resistant material. It was subsequently assessed that the boilers were fit for service as no other damage affecting structural integrity was observed. The defective headers were assessed as not being related to the boiler level indication anomalies. Following completion of this work the reactor was returned to operation.
The basic rating of Level 1, on degradation of defence in depth due to structural defect that could result in various initiators, was uprated to level 2 on the additional factor of an inadequate surveillance program for the EWS headers.

Event date: Fri, 04-10-1996
Nuclear event report
Legenda & explanation