PNO-III-02-006, Significant Metal Loss Observed in Reactor Vessel Head
| ML020670776 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse  |
| Issue date: | 03/08/2002 |
| From: | Mel Holmberg, Jeffrey Jacobson NRC/RGN-III |
| To: | |
| Jacobson J | |
| References | |
| PNO-III-02-006 | |
| Download: ML020670776 (1) | |
March 8, 2002 PRELIMINARY NOTIFICATION OF EVENT OR UNUSUAL OCCURRENCE -- PNO-III-02-006 This preliminary notification constitutes EARLY notice of events of POSSIBLE safety or public interest significance. The information is as initially received without verification or evaluation, and is basically all that is known by the Region III staff on this date.
Facility Davis-Besse Nuclear Power Plant FirstEnergy Corporation Oak Harbor, Ohio Docket: 50-346 Licensee Emergency Classification Notification of Unusual Event Alert Site Area Emergency General Emergency x Not Applicable
SUBJECT:
SIGNIFICANT METAL LOSS OBSERVED IN REACTOR VESSEL HEAD DESCRIPTION:
During recent ultrasonic examination of vessel head penetration (VHP) nozzles required by NRC Bulletin 2001-01 "Circumferential Cracking of Reactor Pressure Vessel Head Penetration Nozzles," dated August 3, 2001, the licensee identified that five VHP nozzles required repair due to cracking in the nozzle adjacent to the J-welds which attach the VHP nozzles to the vessel head. The repair procedure involved machining the cracked portion of the tubes and placing a new weld between the tube and the vessel head.
On March 5, 2002, during VHP nozzle repair activities, the licensee identified an unexpected rotation and lateral movement of one of the nozzles during the machining operation. On March 6, the licensee removed the VHP nozzle and discovered significant metal loss in the head adjacent to the VHP nozzle. The area of the metal loss is not easily observable because of permanent insulation on the exterior of the vessel head.
The licensee has begun to assess the extent of the damage and has formed a root cause team to investigate the cause of this phenomenon. Repair or replacement options are being considered.
The resident inspectors are monitoring the licensees ongoing assessment activities. Region III (Chicago) will conduct follow-up inspections which will focus on extent of condition, causal factors, and repair or replacement activities.
The reactor is currently in a refueling outage, in Mode 6 (Refueling), and depressurized.
The State of Ohio will be notified. The information in this preliminary notification has been reviewed with licensee management.
There has been news media interest in the licensees VHP nozzle inspection activities.
This information is current as of 4:00 p.m. (CST) on March 8, 2002.
CONTACTS:
Melvin Holmberg John Jacobson 630/829-9748 630/829-9736