ML091690635
| ML091690635 | |
| Person / Time | |
|---|---|
| Site: | Oyster Creek |
| Issue date: | 11/07/2008 |
| From: | Richmond J NRC Region 1 |
| To: | O'Hara T NRC Region 1 |
| References | |
| FOIA/PA-2009-0070 | |
| Download: ML091690635 (6) | |
Text
Elizabeth Keighley From:
John Richmond, R-.
Sent:
Friday, November 07, 2008 7:28 AM To:
Timothy OHara Cc:
John White; Richard Conte
Subject:
RE: Oyster Creek Drywell Shell Coating Issue your 'questions are on target. I continue to value your input and guidance. I checked with Pete Tamburro a couple of days ago. He told me that in Bay 11, there were only 2 plugs, one high and one low. So it's easy to know that they've got the correct one. However, I'll look at the UT sheets for verification [when I get them].
From: Timothy OHara Sent: Thursday, November 06, 2008 9:01 PM To: John Richmond Cc: John White; Richard Conte
Subject:
RE: Oyster Creek Drywell Shell Coating Issue
- John, If memory serves, there was more than one plug used in the drywell when core samples were taken in 1986 -1 think there were 8 plugs. Assuming that you're sure they've identified the correct plug and have an understandable way to show that they have the correct location of the coating defect, in relation to the correct pluc and the thickness measurement, that should be ok.
Sorry to belabor the point, just want to make sure it all adds up.
Tim OHara From: John Richmond Sent: Thursday, November 06, 2008 11:36 AM To: Timothy OHara Cc: John White; Richard Conte
Subject:
RE: Oyster Creek Drywell Shell Coating Issue Tim, Do you think that the use of a core plug, observable on both sides of the drywell shell, is inadequate as a reference mark, to get to the correct location? The core plug is a few inches away from the coating defects in the sand bed, and [AmerGen says the same core plug] is within the 7x7 array identified as location 11A.
From: Timothy OHara Sent: Thursday, November 06, 2008 8:43 AM To: John Richmond Cc: John White
Subject:
RE: Oyster Creek Drywell Shell Coating Issue
- John, The original drywell plate thickness was 1.115" nominal. A reading of approx. 0.80" would indicate significant corrosion had occurred, hopefully in the past.
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Tim OHara From: John Richmond Sent: Thursday, November 06, 2008 7:32 AM To: Timothy OHara Cc: John White; Richard Conte
Subject:
RE: Oyster Creek Drywell Shell Coating Issue All excellent questions.
Yesterday morning, I was told a dynamic scan UT had been performed on night shift [presumably by an NDE technician not previously involved with taking drywell shell UTs at 11 ft elevation], near interior location 11 A.
The minimum thickness reading was verbally reported as 0.8 inches. As of COB yesterday, no documentation yet.
The defects (4 separate locations in a small area) are located near a core plug in the shell, so they should be able to locate the area of the defects with pretty good accuracy. Only question I have is whether the drywell floor curb will be an interference item. and prevent them from takinq the readinqs at the proper elevation.
(b)(5)
From: Timothy OHara Sent: Wednesday, November 05, 2008 9:59 PM To: John Richmond Cc: John White; Richard Conte
Subject:
RE: Oyster Creek Drywell Shell Coating Issue
- John, What was the result of the UT measurement of the shell thickness which was done from the inside - per your summary below from 11/3?
Did Amergen document the elevation of the UT measurement in relation to the defect on the outside of the drvwell? How did they control the radial location to be sure they were measuring the actual defect?
Tim OHara From: John Richmond Sent: Wednesday, November 05, 2008 9:02 PM To: Marsha Gamberoni; Darrell Roberts; Ronald Bellamy; Richard Conte; David Pelton; Mary Baty; James Davis; John White Cc: Stephen Pindale; Justin Heinly; Jeffrey Kulp; Timothy OHara; Michael Modes; Glenn Meyer; Paul Kaufman; Heather Jones
Subject:
Oyster Creek Drywell Shell Coating Issue Oyster Creek Drywell Sand Bed Bay 11 Coating Defects Nov 5 AmerGen initiated their repair plan this evening. The one loose blister previously identified by AmerGen was excavated, along with 3 other adjacent bumps identified by NRC inspection. Surface rust, on the drywell shell, was easily recognizable under all 4 locations. The 4 locations are within a 1 to 2 inch oval of each other. The 2
3 bumps, which AmerGen initially characterized as surface irregularities, were tightly adhered, and were difficult to "pop off' (e.g., the technician said it took a lot of force to dislodge them). The blister was easily removed intact. The exposed drywell shell (4 locations) was lightly sanded, generally resulting in a clean bright metal surface. Under 2 of the locations, the exposed surface had an inverted cone shape, with the point of the cone going into the plate steel. There appeared to be a small pit at the center of the cones.
The original rust stain, about 6 inches long, was scrapped off, and the scrapings collected into a bag for lab analysis. The broken blister, originally described as a carbuncle, was collected mostly intact, also for lab analysis.
AmerGen's coating expert, Jon Cavallo, Corrosion Control Consultants & Labs, described the three layer coating as follows: (1) a clear primer, (2) a reddish brown epoxy layer, applied by roller, and (3) a grayish white epoxy layer applied by roller. Jon believes that the 2 epoxy layers should be 6 to 10 mils each, and that the three layer coating system would therefore be 12 to 18 mils in thickness. As a comparison, Jon said that a normal piece of copy paper is about 3 mils thick, so he expected the total coating thickness to be equivalent to about 3 sheets of paper. Jon believes the lab analysis will adequately determine the coating thickness of the collected scrapings and samples.
John Richmond From: John Richmond Sent: Monday, November 03, 2008 7:51 PM To: Marsha Gamberoni; Darrell Roberts; Ronald Bellamy; Richard Conte; David Pelton; Mary Baty; James Davis;. John White Cc: Stephen Pindale; Justin Heinly; Jeffrey Kulp; Timothy OHara; Michael Modes; Glenn Meyer; Paul Kaufman
Subject:
RE: Oyster Creek Drywell Shell Coating Issue S"bmmary of Conference Call between Exelon and NRC staff, regarding OC Drywell Sand Bed Bay-1 1 repair plans.
During an interactive discussion (questions and answers), Exelon Stated:
- 1) Detailed plan is still being developed, which will include:
- a. Opportunities for NRC observations during excavation and examination of the defect
- b. Chemical analysis to attempt to determine whether the surface stain contains iron
- c. Will carefully remove top loose layers to help determine whether there is any on-going drywell shell corrosion
- d. Will excavate an area maybe an inch in diameter, which should include any very close surface irregularities
- 2) No additional extent-of-condition was needed, to determine whether there are any blisters (carbuncles) in any other areas or other sand bed bays. A 100% coating examination had already been performed and no other defect or indication had been identified.
- 3) There is only one blister (about 1/4 inch in diameter), as documented on the VT-1 Examination Record.
There are no other blisters or carbuncles, as suggested by the NRC inspection of Nov 2. The inspector's observations must have been "bumps" that are just surface irregularities.
- 4) The coating has no service life. Epoxy coatings at some nuclear plants have been in-service, without any significant failures, for about 40 years. In non-nuclear industry, epoxy coating service life is typically an economic issue, and those coatings are often in very severe environments.
- 5) Some type of industry standard adhesion test might be done around the indication, prior to re-applying the new coating. A Dolly Adhesion Test [??] was considered too hard to perform. However, a modified knife edge test might be doable.
3
- 6) An ultrasonic test (UT) will be performed (maybe tonight), from the inside of the drywell, at the location of the coating defect.
If I left anything out, please feel free to add it in.
John Richmond From: John Richmond Sent: Sunday, November 02, 2008 6:41 PM To: Marsha Gamberoni; Darrell Roberts; James Clifford; Ronald Bellamy; Richard Conte; Marc Dapas; John White Cc: David Pelton; Stephen Pindale; Justin Heinly; Jeffrey Kulp; Timothy OHara; Michael Modes; Glenn Meyer; Paul Kaufman
Subject:
Oyster Creek Drywell Shell Coating Issue OC License Renewal Outage Commitments Inspection Drywell Shell (steel liner) Coating Issue Exterior Drywell Shell in Sand Bed Bay 11 On Oct 31, during a routine coating inspection, AmerGen identified a coating defect. NDE VT Examination Record documented a "Pinhole Carbuncle,. 1/4 inch in diameter, with Evidence of Leakage (Rust Line) 6 inches Long. 16 inches right of Opening [access tunnel], 34 inches from Moisture Barrier [floor in sand bed cavity]."
The carbuncle was verbally described as a small blister, soft to the touch. The leakage was verbally described as a "bleed through" 6" long tear drop shaped surface stain, brownish in color, and dry to the touch.
A repair work order is being prepared. Repairs are scheduled for Nov 4. Per engineering specification, the coating defect will be removed using mechanical tools, such as pencil grinder, rotary file, flapper wheel, etc
[e.g., skill of the craft]. Prepare the substrate and feather the edges, then apply two layers of new coating
[Devoe epoxy]. The Issue Report contains additional requirements, not yet in the work order, including (1) document the extent of the damage, and how deep the blister has formed into the coating, (2) verify plate thickness in the area of the coating failure meets acceptance criteria [e.g., do a UT from inside the drywell],
and (3) document with pictures as loose coating layers are removed.
The carbuncle, on the exterior surface of drywell shell, is very close to ultrasonic test'(UT) location 1 1A, inside the drywell at elevation 11 ft. 3 in. UT location 11 A is a 7x7 array (6"x6" grid). The carbuncle is located about 3 inches from a core plug that is in the 7x7 array. AmerGen estimates that the carbuncle is about 1 inch from the edge of the array. Therefore, it's reasonable to expect that a good UT can be done from inside the drywell at the location of the defect outside the drywell.
Sand Bed Bays 1, 11, and 13 were previously identified as the bays with the most significant corrosion (e.g.,
thinnest shell). The epoxy coating system was applied in 1992, and was 3 layers thick. The total thickness is believed to be about 25 mils. The first post-installation coating inspection was last outage, in 2006. This is only the second coatings inspection since 1992. In 2006, no coating defects were identified. This outage (2008), only this one coating defect was identified.
All sand bed bays have been NDE UT and VT examined this outage (not all NDE examination records have been prepared). No other potential coating defects were identified. Some cracks in the floor epoxy sealer and in the moisture barrier seal were identified, and are planned to be reworked.
On Oct 29 & 30 (prior to the defect being identified), Tim O'Hara inspected sand bed Bay 1, 5, 11, and 13.
Tim's inspection was not a full entry inspection: he did a general visual inspection from the tunnel opening, without entering the cavity. Tim did not identify any issues or concerns in bay 11, and only floor cracks in one other bay were identified.
4
On Nov 2, I did a full entry inspection of Bay 11 & 13, which also extended partly into Bays 9 & 15. There appears to be 2 or 3 small carbuncles in a cluster, next to the one that's bleeding. The NDE tech, when interviewed, also described a cluster of carbuncles, although the NDE dais sheet only described the largesti onp. Ldid not identify any other potential indications or problems.
John Richmond OC NRC Team Roorrt 609-971-4830 5
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([148.184.99.10]) with mapi; Fri, 7 Nov 2008 07:27:31 -0500 Content-Type: application/ms-tnef; name="winmail.dat" Content-Transfer-Encoding: binary From: John Richmond <John.Richmond@nrc.gov>
To: Timothy OHara <Timothy.OHara@nrc.gov>
CC: John White <John.White@nrc.gov>, Richard Conte <Richard.Conte@nrc.gov>
Date: Fri, 7 Nov 2008 07:27:30 -0500
Subject:
RE: Oyster Creek Drywell Shell Coating Issue Thread-Topic: Oyster Creek Drywell Shell Coating Issue Thread-Index:
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