ML020920750
| ML020920750 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse  |
| Issue date: | 03/29/2002 |
| From: | NRC/IRO |
| To: | International Atomic Energy Agency (IAEA) |
| References | |
| Download: ML020920750 (2) | |
Text
THE INTERNATIONAL NUCLEAR EVENT SCALE (INES)
EVENT RATING FORM (ERF)
TO BE SENT TO THE IAEA INES CO-ORDINATOR BY
! FAX: + 43 1 2060 29723
! PHONE: + 43 1 2060 22685 IAEA, WAGRAMERSTRASSE 5. P.O. BOX 100, A-1400 VIENNA, AUSTRIA
! E-MAIL: D.J.C.DELATTRE@IAEA.ORG EVENT TITLE UNEXPECTED DETERIORATION OF REACTOR VESSEL HEAD MATERIAL IN VICINITY OF PENETRATION EVENT DATE 08.03.02 RATING PROVISIONAL O FINAL G GG G
RATING DATE OUT OF SCALE BELOW SCALE ON SCALE SAFETY ATTRIBUTE DEGR. DEFENCE IN-DEPTH O
0 1
2 3
4 5
6 7
ON-SITE IMPACT 29.03.02 O
OFF-SITE IMPACT COUNTRY USA FACILITY NAME DAVIS-BESSE NUCLEAR POWER STATION FACILITY TYPE PWR ASPECTS OF SIGNIFICANCE TO THE PUBLIC:
YES NO ACCIDENT G INCIDENT O DEVIATION G RADIOACTIVE RELEASES OFF-SITE G
O RADIOACTIVE RELEASES ON-SITE G
O WORKERS INJURED BY RADIATION G
O WORKERS INJURED PHYSICALLY G
O PLANT SAFETY IS UNDER CONTROL O
G THE EVENT REPORTED IS A DISCOVERY OF A DEFICIENCY BY ROUTINE SURVEILLANCE G
O A PRESS RELEASE WAS MADE O
G (IF YES, PLEASE ATTACH IT)
SHORT DESCRIPTION OF THE EVENT: 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 repaired. The licensee had performed 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 an approximately 6.5 inch thickness of carbon 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 5 inches by 7 inches. The reactor vessel head material in this area had been reduced to a minimum thickness of less than 0.3 inches, which is the thickness of the cladding.
JUSTIFICATION OF THE RATING: This event was rated in accordance with Section IV-3.2.3 of the INES User's Manual "Potential Events (including structural defects)". The potential initiator (major LOCA) is considered to be an unlikely occurrence. According to Table III, this event, with safety function operability within Operating Limits and Conditions (applicable due to normally scheduled outages of safety equipment during long periods of operation of the unit) results in a base rating of 2/3.
A rating of level 3 was chosen based upon the extent of the structural degradation and the increased possibility of a structural failure. Since the basic rating of level 3 was obtained using the impact on defense in depth, no additional escalation was warranted. However, the inspection revealing the condition was not part of the normal surveillance inspection process at this facility and the discovery of the degraded condition occurred only during inspections specifically required by the regulator.
CONTACT PERSON FOR FURTHER INFORMATION NAME Joseph J. Holonich ADDRESS USNRC, Washington, DC 20555 PHONE (301) 415-7482 FAX (301) 816-5151 PLEASE ATTACH ADDITIONAL INFORMATION ON JUSTIFICATION OF THE EVENT RATING AND DIFFICULTIES ENCOUNTERED, IF NEEDED
ENCLOSURE 1