ML021080205
| ML021080205 | |
| Person / Time | |
|---|---|
| Site: | Surry, North Anna  |
| Issue date: | 03/06/2002 |
| From: | Christian D Dominion Energy Co |
| To: | Office of Nuclear Reactor Regulation |
| References | |
| RIS-02-001 | |
| Download: ML021080205 (24) | |
Text
RIC 2002 W1 Circumferential Cracking of Reactor Vessel Head Penetration Nozzles David A. Christian Senior Vice President & Chief Nuclear Officer Dominion Energy March 6, 2002
2 Dominion Response to Bulletin
- Would perform 100% effective visual inspection for NAPS 1 and SPS 1 during fall RFO and 100% NDE on NAPS 1 (if equipment reliable)
- Based on inspection results, decision was made to inspect all units by year end in accordance with bulletin recommendation
- Supplemental response to bulletin provided results of plant specific analysis for SPS and NAPS which qualified visual examination
3 North Anna Unit 1 100% qualified visual performed Heavy boric acid deposits on 50% of head (active canopy seal weld leak found at shutdown)
Crawler unreliability in part due to debris on head 34 of 65 penetrations with relevant boric acid deposits
4 North Anna Unit 1
- NDE campaign
- Eddy Current (EC) plan based on visual results
- Delivery system unreliable therefore could not obtain NDE data on 100% of penetrations
- Access was limited due to unique centering rings
- Ultrasonic Testing (UT) performed based on EC results
- 6 of 8 tubes with EC recordable indications inspected with UT -
very shallow axial indications, other 2 were conservatively sized based on 2:1 aspect ratio
- Result showed EC conservatively sized indications
- Tubes dispositioned by flaw evaluation
5 North Anna Unit 1
- NDE campaign (continued)
- Liquid Penetrant (LP) utilized to disposition J-groove weld recordable indications
- 3 of 5 penetrations examined with manual LP
- 2 of 5 penetrations accepted by review of EC data compared to LP results
- NDE Level III determined indications in clad material
6 North Anna Unit 1
- Penetration 50
- Penetration not in boric acid field from canopy seal weld leak
- EC of tube showed non-recordable indications in tube (98% coverage)
- EC showed 4.3 mm indication in the clad (not recordable)
- UT of tube ID - no recordable indications but limited to 97 degrees
- LP of weld - indications in clad and crater crack in the weld (crater crack was ground out)
- Removed thermal sleeve to obtain full access - full access UT revealed no recordable indications including a circumferential UT scan
North Anna Unit 1 Boric acid from canopy seal weld leak (pen 53)
Boric acid from canopy seal weld leak (pen 53)
Penetration 33 Penetration 33
North Anna Unit 1 Nozzle 50
9 North Anna Unit 1 Results No through wall indications Shallow indications do exist on tube ID which need to be monitored for growth rate (unknown if PWSCC)
Visual inspection complicated by large amount of boric acid on the reactor vessel head from other sources NDE inspection complicated due to interferences (centering ring and anti-ejection ring)
Inspections complicated by delivery equipment unreliability therefore equipment was partially redesigned and rebuilt between North Anna outages NRC representatives reviewed all NDE data on site Dose expended: 18 man-rem
10 Surry Unit 1
- 100% qualified visual performed
- Less debris noted than North Anna 1
- 27 of 65 penetrations initially rejected
- 13 of 27 accepted when debris was easily removed by 40 psi compressed air (technique introduced by vendor, used elsewhere and verbally endorsed by NRR)
- 4 of 27 accepted when debris removed by 60 psi air plus satisfactory UT
- Leaving 10 penetrations from visual campaign as rejected visual
11 Surry Unit 1
- NDE campaign
- Axial UT probe used on 16 penetrations (including 6 cleared by air). No reportable indications
- Circumferential UT probe used on 5 penetrations with LP indications in J-groove weld. No reportable indications
- Vendor had no remote J-groove weld inspection capability
- Manual liquid penetrant (LP) on 10 penetrations
- 2 penetrations had circumferential LP indications in center of the weld, highly branched in appearance (penetration 27 had wet boron deposits on top)
- 4 penetrations had rejectable indications that could not be ground out
- 4 penetrations had indications that were ground out and accepted
12 Surry Unit 1 Results 6 penetrations were reported to the NRC as a non-emergency 8-hour report in accordance with 10 CFR 50.72(b)(3)(ii)(A) and 50.73(a)(2)(ii)(A), a condition that results in a principal safety barrier being seriously degraded All indications confined to weld, hasnt propagated to tube All 6 penetrations repaired Dose expended: 161 man-rem Templating performed for future head replacement
Surry Unit1
Surry Unit 1 Nozzle 27
Surry Unit 1
Surry Unit 1 Penetration 40
17 North Anna Unit 2
- Performed 100% qualified visual inspection
- Head extremely clean
- 6 penetrations initially rejected
- 3 of 6 cleared debris with air
- 3 penetrations could not be cleared with air
18 North Anna Unit 2
- NDE campaign
- Thermal sleeves removed on penetration 62, 63 to facilitate inspection (penetration 51 is T/C)
- Performed EC in tube - indications on all tube IDs
- Performed axial and circumferential UT - axial indications shallow and accepted by flaw evaluation
- Bypassed EC in J-groove weld and went straight to LP examination. Indications in clad believed to be from original fabrication similar to Unit 1
- Manual grinding and then remote grinding on penetration could not clear indication
- Temperbead and embedded flaw relief requests approved as repair methodology for all 3 penetrations
19 North Anna Unit 2
- NDE campaign (continued)
- Boat sample removed from one penetration
- Failure analysis revealed solidification or hot cracking confined to the Alloy 182, or butter, material.
- A few of the hot cracks were connected to the wetted surface.
- Some PWSCC noted which may have connected the hot cracking to the surface or may have occurred after the hot cracking connected to the surface
- Ringhals Unit 2 found fabrication flaws between J-groove weld preparation and vessel in 1992. Identified after grind out of penetration 63
- Dose expended: 69.947 man-rem
20 North Anna Unit 2
21 North Anna Unit 2
22 North Anna Unit 2 Penetration 63 -LP results after grinding
23 Surry Unit 2
- 100% qualified visual complete
- 3 penetrations masked and cleared with air
- No NDE inspection needed
24 Summary
- Reactor heads were cleaned and as-left condition documented
- Currently evaluating lessons learned
- Develop future strategies (inspection, repair, replacement)
- Push for better inspection technique in weld for flaw characterization
- Stay close to industry and regulator