ML091380251
| ML091380251 | |
| Person / Time | |
|---|---|
| Site: | Catawba  |
| Issue date: | 03/24/2009 |
| From: | NRC/NRR/DCI |
| To: | |
| Wong, Emma - NRR/DCI/CSGB, 415-1217 | |
| References | |
| Download: ML091380251 (4) | |
Text
Catawba Unit 2 EOC 16 Stream Generator Inspection Results NRC Update - March 24, 2009 Purpose To informally communicate to the NRC staff the results of the Catawba Unit 2 EOC16 steam generator inspection. Since the inspection is still in progress, the results discussed in this update should be considered preliminary (for information only).
General Information
- Westinghouse Model D-5 steam generators with Alloy 600TT tubing
- Inspection being performed by Westinghouse
- Inspection being performed with bobbin, array, and rotating coil (selected locations)
- Prior outage indications of PWSCC at high stress locations (tube end, tack expansion)
- Prior outage indications of AVB wear - slow and predictable Inspection Scope
- Bobbin coil examination of all tubes full length except Row 1-5 u-bend region
- 35% sample of Row 1-5 u-bend region with array probe
- 100% of hot leg tubesheet region with array probe (all SGs)
- 100% of cold leg tubesheet region with array probe (SG A and D)
- 20% sample of cold leg tubesheet region with array probe (SG B and C)
- 20% sample of Row 10 u-bend region with array probe
- 50% sample of all existing dents with array probe
- Any new dents with array probe
- 20% sample of pre-heater expansions with array probe
- All hot leg tube support locations for Seabrook type tubes with array probe
- Periphery tubes two rows deep with array probe
- Bounding inspections two tubes around all new PLP indications confirmed with array
- RPC inspection of any tube end indication identified for plugging with array probe (for IARC sizing)
- RPC inspection of top-of-tubesheet indications identified with array probe
- RPC inspection of tube support indications identified with array probe Expansion criteria: Expand inspection scope to 100% for any planned sample population less than 100% where crack-like degradation is detected
Page 2 of 4 Current Status SG A - Inspection 80% Complete SG B - Inspection Complete SG C - Inspection 99% Complete SD D - Inspection 75% Complete Inspection Results Catawba Unit 2 EOC 16 Inspection Summary of Crack-Like Indications (# of tubes)
Steam Generator A B C D HL CL HL CL HL CL HL CL Top of Tubesheet 10* 0 0 0 2* 0 1* 0 OXP's/Bulges 0 0 0 0 0 0 0 0 Below IARC Depth (axial) 1 0 155 0 8 0 4 0 Below IARC Depth (circ) 6* 0 11 0 1* 0 5* 0 TSP Locations 0 0 1 0 0 0 6* 0
- Not yet inspected with +Point AVB wear continues to be slow and predictable.
Repair Scope SG A - To be determined SG B - 6 tubes with tube-end circ cracks 94°, 1 tube with TSP indication SG C - To be determined SG D - To be determined NRC Generic Questions
- 1. Discuss any trends in the amount of primary-to-secondary leakage observed during the recently completed operating cycle.
There has been no primary-to-secondary leakage during the recently completed operating cycle.
3/24/09
Page 3 of 4
- 2. Discuss whether any secondary side pressure tests were performed during the outage and the associated results.
No secondary side pressure testing has been performed. None is planned.
- 3. Discuss any exceptions taken to the industry guidelines.
No exceptions have been taken to the EPRI PWR Steam Generator Examination Guidelines.
- 4. For each steam generator, provide a description of the inspections performed including the areas examined, the probes used, and the expansion criteria. Also, discuss the extent of rotating probe inspections performed in the portion of the tube below the expansion transition region.
See above discussion.
- 5. For each area examined, provide a summary of the number of indications found to date for each degradation mode. For the most significant indications in each area, provide an estimate of the severity of the indication. In particular, address whether tube integrity was maintained during the previous operating cycle. In addition, discuss whether any location exhibited degradation mode that had not previously been observed at this location in this unit.
See summary of inspection results above.
The indication(s) at the TSP location is a type of degradation not previously seen at Catawba Unit 2. The tube(s) with this apparent degradation are in a small population of tubes that have characteristics similar to the Seabrook tubing that experienced this type of degradation (inadequate heat treatment).
- 6. Describe repair/plugging plans.
Confirmed tube end crack-like indications meeting IARC criteria will be plugged.
Confirmed top of tubesheet crack-like indications will be plugged and stabilized.
Confirmed crack-like indications at support plate locations will be plugged and stabilized.
Volumetric degradation >40% TW will be plugging and stabilized.
- 7. Describe in-situ pressure test and tube pull plans and results.
No in-situ pressure testing is required. None is planned.
It had been planned to remove two tube samples from the B steam generator for verification and investigation of previously identified top of tubesheet ODSCC. No indications were seen this outage, prompting the tube pull to be cancelled.
3/24/09
Page 4 of 4
- 8. Provide the schedule for steam generator related activities during the remainder of the current outage.
- Complete eddy current testing (Wednesday-Friday)
- Perform tube plugging and stabilization as required (Tuesday-Saturday)
- 9. Discuss the following regarding loose parts: What inspections are performed to detect loose parts, a description of loose parts identified and their location within the steam generator, if loose parts were removed, tube damage associated with loose parts, and the source or nature of the loose parts.
A planned FOSAR inspection was implemented in the pre-heater section of each steam generator where foreign objects tend to collect. A number of very small objects were identified in this region. Most of these objects are believed to be legacy material residing in the steam generators. A number of these objects were removed. Some were not removed, but technically evaluated as acceptable for another cycle of operation. No tube wear has been detected due to foreign objects.
- 10. For OTSGs, if you have Babcock& Wilcox welded plugs installed in the steam generators, discuss the actions taken in response to Framatomes notification of the effect of tubesheet hole dilation on the service life of the welded plugs.
Not applicable.
- 11. For OTSGs, discuss any actions taken in response to the severed tube issue during the outage (reference NRC IN 2002-02).
Not applicable.
3/24/09