ML080800039
| ML080800039 | |
| Person / Time | |
|---|---|
| Site: | Palo Verde, Braidwood, Summer, Seabrook, Vogtle, Waterford, South Texas, Comanche Peak  |
| Issue date: | 03/13/2008 |
| From: | Ted Sullivan NRC/NRR/ADES/DCI |
| To: | |
| Markley M, NMSS/IMNS/MSIB (301) 415-5723 | |
| Shared Package | |
| ml080800024 | List: |
| References | |
| Download: ML080800039 (9) | |
Text
1 Pressurizer Dissimilar Metal Butt Weld Inspections Ted Sullivan, SLS Division of Component Integrity Office of Nuclear Reactor Regulation March 13, 2008
2 Background
- Knowledge of degradation of nickel base alloys since 1980s
- Cracking in Alloy 82/182 butt welds has been experienced at multiple plants since 2000
- In October 2006, extensive circumferential flaws were identified in pressurizer nozzle welds at Wolf Creek
3 Wolf Creek Analyses Commitments to implement enhanced leakage monitoring and shut down by end of 2007 to mitigate/inspect
- Confirmatory action letters Advanced Finite Element Analyses (AFEA)
- Plant specific information obtained to do analyses
- NRC analyses encompassed all 9 plants
- NRC performed analyses of over thirty cases
- Purpose to review, critique and extend industry analyses
- Industry analyses independent from NRC staff analyses
- Most comprehensive, state of the art analyses of flaw growth in weld ever undertaken; thousands of hours of work
- Involved highest level of expertise in the US
- Results predicted acceptable margins between potential flaw growth to detectable leakage and a rupture condition Decision to allow operation of 9 plants until June 2008
4 NRC AFEA Surge Nozzle Case
5 Plants Addressed by AFEA
- Braidwood 2
- Comanche Peak 2
- (Diablo Canyon 2)
- Palo Verde 2
- Seabrook
- South Texas 1
- V.C. Summer
- Vogtle 1
- Waterford 3
6 Retired Pressurizer Inspection Donated to NRC for research program Inspections performed to determine the research value of the welds Indications found by dye penetrant (PT) & manual phase array ultrasonic examination (UT) 5 of 6 Nozzles had circumferential & axial indications Spray & surge nozzles had linear circ indications Safety nozzles had 360o indications with non-uniform depths around circumference with deepest:
- 80% on the A Safety nozzle
- 75% on the B Safety nozzle
- 69% on the C Safety nozzle
7 Retired Pressurizer Inspection
- Details received late on March 4, 2008 contained a flaw profile and UT images at measurement locations
8 Flaw Profile in March 4th report: A Safety Nozzle Weld
9 Actions Taken
- Report reviewed by NRC in-house and contracted experts
- Inspection results led to staff questions concerning the severity of the indications represented by the profile and the cause of the UT signals
- Profile raised questions about the basis to allow the remaining 8 plants to operate until the spring 2008 outages