05000338/LER-2003-001
| Document Hunger | |
| Event date: | 03-04-2003 |
|---|---|
| Report date: | 04-24-2003 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded |
| 3382003001R00 - NRC Website | |
—r-- DOCKET LER NUMBER16) � //UMBER FACILITY NAME (1) PAGE (3) 1.0 DESCRIPTION OF THE EVENT On February 22, 2003, at 2100 hours0.0243 days <br />0.583 hours <br />0.00347 weeks <br />7.9905e-4 months <br /> Unit 1 was ramped offline for a scheduled refueling outage. On March 4, 2003, at 0854 hours0.00988 days <br />0.237 hours <br />0.00141 weeks <br />3.24947e-4 months <br />, with Unit 1 defueled, an apparent reactor vessel head through-wall leak was noted during visual inspection of penetration 50 (EIIS System AB, Component PEN). The reactor vessel head (EIIS Component RPV) was being visually inspected at penetration 50 to follow up on inspection results from the previous outage in 2001. Penetration 50 was found to exhibit boric acid approximately one half inch in diameter at the lower side of the penetration-to-head transition. There was no sign of wastage on the reactor vessel head. This through wall leak has been assessed as a degradation of a principal safety barrier in accordance with 10 CFR 50.72(b)(3)(ii)(A). An 8-hour Non-Emergency Report was made to the NRC at 1033 hours0.012 days <br />0.287 hours <br />0.00171 weeks <br />3.930565e-4 months <br /> on March 3, 2003. The event is reportable in accordance with 10CFR50.73(a)(2)(ii)(A).
In addition, Technical Specification (TS) 3.4.6.2 prohibits reactor coolant system (RCS) (E1IS System AB) pressure boundary leakage in Modes 1 through 4. Although the apparent leakage was identified with the unit defueled, it is reasonable to assume that the leakage occurred during Modes 1 through 4. This event is also reportable in accordance with 10CFR50.73(a)(2)(i)(B) for a condition prohibited by TS.
Notification was made to the NRC in a letter dated January 23, 2003 noting the decision to replace the Unit 1 reactor vessel head during the 2003 refueling outage.
Consequently, no additional inspections were planned or performed for the existing reactor vessel head and penetration nozzles.
2.0 SIGNIFICANT SAFETY CONSEOUENCES AND IMPLICATIONS No significant safety consequences resulted from this event since RCS unidentified leakage was well below Technical Specification limits. Reactor Coolant System leakage, including unidentified leakage, is quantified every 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> per TS 3.4.6.2. Prior to the Unit 1 shutdown, unidentified leakage was measured at 0.08 gpm and containment sump inleakage was measured at 0.12 gpm.
With the apparent cause believed to be hot short cracking WCAP-14552, "Structural Evaluation of Reactor Vessel Upper Head Penetrations to Support Continued Operation:
North Anna and Suny Units," previously documented that as much as 83.9% of a weld may be unfused, and the allowable stress limits can still be met. Even a complete lack of fusion in the zone between the weld and the head would not result in rod ejection because the weld to the tube would prevent it. Therefore, catastrophic failure of a penetration is unlikely. The health and safety of the public were not affected at any time during this event.
FACILITY NAME (1) NORTH ANNA POWER STATION UNIT 1 DOCKET LER NUMBER 16) PAGE (3) L 1 SEQUENTI
AL I REVISION
3.0 CAUSE The apparent cause of the Penetration 50 leakage was hot-short cracking, which occurred during original fabrication of the reactor vessel head. The leakage was accelerated by primary water stress corrosion cracking.
4.0 IMMEDIATE CORRECTIVE ACTION(S) An 8-hour Non-Emergency Report was made to the NRC at 1033 hours0.012 days <br />0.287 hours <br />0.00171 weeks <br />3.930565e-4 months <br /> on March 3, 2003.
5.0 ADDITIONAL CORRECTIVE ACTIONS A management decision was made to replace the North Anna Unit I reactor head with one constructed of materials that are known to be more resistant to cracking rather than perform penetration repairs.
6.0 ACTIONS TO PREVENT RECURRENCE Future reactor vessel head inspections will be performed in accordance with our responses to NRC Bulletin 2002-02.
7.0 SIMILAR EVENTS vessel head penetrations.
nozzle through-wall leakage of three reactor vessel head penetrations.
entering the "B" RCP thermal barrier housing. This line is part of the RCS pressure boundary leakage.
8.0 MANUFACTURER/MODEL NUMBER Rotterdam Dockyard Company/Serial Number 30662 9.0 ADDITIONAL INFORMATION None