INES-event
INES 3

DETERIORATION OF REACTOR VESSEL HEAD

On 8 March 2002, with the reactor shut down for a refueling outage, the licensee discovered a significant loss of reactor vessel head base material adjacent to a penetration nozzle that was being inspected. The licensee was performing an inspection of control rod drive nozzles in the reactor vessel head as required by the regulator (US NRC). During the repair of one of the nozzles, the licensee noted some deterioration of the base material surrounding the nozzle. The reactor vessel head is composed of a 6.63 inch thick low alloy steel base material with a stainless steel weld cladding applied to the interior surface. After removal of the nozzle and cleaning of the immediate surrounding area, the licensee discovered significant wastage of the carbon steel material adjacent to the nozzle boring with a total approximate size of 4 to 5 inches x 5 to 7 inches. The reactor vessel head material in this area had been reduced to the thickness of the clad layer, ranging in thickness from 0.24 to 0.38 inches.

Location: DAVIS BESSE-1
Event date: Fri, 08-03-2002
Nuclear event report
Legenda & explanation