05000331/LER-2010-004
| Duane Arnold Energy Center | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded |
| Initial Reporting | |
| ENS 46379 | 10 CFR 50.72(b)(3)(ii)(A), Seriously Degraded |
| 3312010004R01 - NRC Website | |
I. Description of Event:
During the Duane Arnold refueling outage 22 (RF022), ultrasonic (UT) examinations of welds susceptible to IGSCC were performed in accordance with the BWRVIP-75 and ASME Section XI inspection programs. On October 29, 2010, while in Mode 5 and shutdown for RF022 for refueling activities, UT examination of the N2A reactor recirculation riser safe-end to nozzle weld, RRA-F002A, identified a circumferential flaw. The RRA-F002A circumferential weld indication was approximately 6.5" and 71% through-wall (TW) and identified as Inner Diameter (ID) surface connected. As part of the BWRVIP and ASME Section XI Inspection Programs, the inspection population was expanded to determine the extent of condition. There were three additional welds that required examination in accordance with guidance BWRVIP-75. The welds were RRG-F002A, RRF-F002A, and RRH-F002A.
The UT examinations for all three welds were completed with no indications of flaws noted.
RRA-F002A was subsequently overlaid under an NRC verbally approved relief request.
This event was reported to the NRC as an 8 hour9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> event under 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, as documented in Event Notification number 46379.
II. Assessment of Safety Consequences:
This report is being submitted pursuant to 10CFR50.73(a)(2)(ii)(A).
There was no Nuclear Safety Significance due to the indications found in the safe-end to safe-end extension weld. The location maintained the required safety factors per IWB-3640 and the flaw depth to thickness ratio was less than the maximum ASME Code requirement of 0.75. In addition, the location did not result in any violation of the pressure boundary (leak) and has been repaired under an acceptable relief request.
This event did not result in a Safety System Functional Failure.
III. Cause of Event:
The root cause identified was that the 1978 Safe-end Replacements consisted of Alloy 82/182 welding filler metal that is susceptible to IGSCC.
IV. Corrective Actions:
A modification was planned to perform repairs of the safe-end to nozzle welds. The repair was to overlay the flawed weld with material (Alloy 52) resistant to Stress Corrosion Cracking (SCC). The implementation of the overlay required a relief request from the NRC to approve the use of a non-NRC approved code case (N-504-4). The overlay was successfully applied and the ultrasonic examination results were found to be acceptable.
V. Additional Information:
Previous Similar Occurrences:
Previous Similar Occurrences:
1.LER 1999-006, "Indications in Recirculation Riser Nozzle-to-Safe End Welds.
In 1999, stress corrosion cracking was found in two safe-end to nozzle welds (RRB-F002 and RRD- F002). Both of these welds were overlaid using an approved relief request from the NRC.
2. LER 2007-003, "Linear indications found during UT examination of safe-end to nozzle welds.
In 2007, stress corrosion cracking was found in two safe-end to nozzle welds (RRF-F002 and RRC- F002). Both of these welds were overlaid using an approved relief request from the NRC.
EIIS System and Component Codes:
AD - Reactor Recirculation System Reporting Requirements:
This report is being submitted under 10 CFR 50.73(a)(2)(ii)(A)