ENS 44005
ENS Event | |
|---|---|
21:00 Feb 23, 2008 | |
| Title | Unacceptable Flaw in Rpv Cap-To-Pipe Weld |
| Event Description | At 1600 EST, it was determined by a phased array ultrasonic examination that an unacceptable flaw existed in reactor pressure vessel penetration N9. This penetration leads to a capped line and the flaw is in the cap-to-pipe weld. The flaw is 2.3 inches in length and reaches a maximum depth of 43.6 percent through-wall on a 5.75 inch OD pipe. The flaw was discovered during the routine ISI [In-service Inspection] examination of this penetration. The flaw has been found unacceptable per paragraph IWB-3514.4 of the 2003 Addenda of ASME Section XI and is therefore reportable. Upon discovery of the flaw, all penetrations of this type were examined with no further findings.
A weld overlay repair is planned and should be completed by 3/6/08. The licensee notified the NRC Resident Inspector.
On 2/23/2008 event number 44005 was made to report an unacceptable flaw in reactor pressure vessel penetration N9. The assumption made at that time was that the flaw seriously degraded the affected control rod drive (CRD) return line that was capped. This was based on the fact that the flaw was unacceptable from an ASME Section XI perspective and therefore reportable. Based on this assumption the event was reported in accordance with the following reporting requirement. '10 CFR 50.72 (b)(3)(ii)(A) Any event or condition that results in: (A) The condition of the nuclear power plant, including its principal safety barriers, being seriously degraded;' The depth of the flaw was initially reported to be 43.6% through wall and the thickness of the wall was measured to be 0.75 inches. Phased array ultrasonic examinations in accordance with Appendix VIII of Section XI were used to fully interrogate and characterize the circumferentially oriented flaw. The final dimensions were 2.3 inches in length on the inner diameter and a maximum depth of 60% through wall. A flaw evaluation of the Unit 1 CRD return line nozzle cap weld was subsequently performed by Structural Integrity Associates, Inc., to evaluate the 'as-found' condition and to determine the implications of the flaw on the affected system at the time of shutdown. The evaluation considered the flaw size and the appropriate stresses for operation. No crack growth was required to be assumed since the 'as-found' flaw was compared against the allowable flaw size which was used to determine the acceptability of the flaw during plant operation. Since the weld is associated with the capped CRD return line nozzle, the applied stress at the affected location was due to pressure loading only. The flaw evaluation concluded that the requirements of Section IWB-3640 were satisfied for a flaw less than 75% through-wall. The 'as-found' depth of 60% through wall is less than the allowable depth of 75%. Based on this information, the Structural Integrity Associates, Inc. evaluation demonstrated that the flaw was acceptable per the ASME Code Section Xl, 2001 Edition through 2003 Addenda requirements. Since the as- found flaw depth at the N9 weld is less than the allowable flaw depth, the required safety factors were met at all times during plant operation. Based on this updated information the conclusion has been reached that this flaw did not seriously degrade the plant or its principal safety barriers. Since the condition does not meet a reporting requirement, this notification serves to retract Notification # 44005 made on 2/23/2008. The licensee notified the NRC Resident Inspector. |
| Where | |
|---|---|
Hatch  Georgia (NRC Region 2) | |
| Reporting | |
| 10 CFR 50.72(b)(3)(ii)(A), Seriously Degraded | |
| Time - Person (Reporting Time:+-3.23 h-0.135 days <br />-0.0192 weeks <br />-0.00442 months <br />) | |
| Opened: | Tony Spring 17:46 Feb 23, 2008 |
| NRC Officer: | John Knoke |
| Last Updated: | Mar 20, 2008 |
| 44005 - NRC Website
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WEEKMONTHYEARENS 569592024-02-11T15:11:00011 February 2024 15:11:00
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