ML041660086
| ML041660086 | |
| Person / Time | |
|---|---|
| Site: | Vogtle  |
| Issue date: | 06/10/2004 |
| From: | Gratton C NRC/NRR/DLPM/LPD2 |
| To: | Gasser J Southern Nuclear Operating Co |
| Gratton C, NRR/DLPM, 415-1055 | |
| References | |
| TAC MC3046, TAC MC3047 | |
| Download: ML041660086 (7) | |
Text
June 10, 2004 Mr. J. T. Gasser Vice President Southern Nuclear Operating Company, Inc.
Post Office Box 1295 Birmingham, Alabama 35201-1295
SUBJECT:
VOGTLE ELECTRIC GENERATING PLANT, UNIT 2 -
SUMMARY
OF CONFERENCE CALL WITH SOUTHERN NUCLEAR OPERATING COMPANY REGARDING THE 2004 STEAM GENERATOR TUBE INSPECTION RESULTS (TAC NOS. MC3046 AND MC3047)
Dear Mr. Gasser:
On May 4, 2004, the Nuclear Regulatory Commission (NRC) staff participated in a conference call with members of the Southern Nuclear Operating Company, Inc. (the licensee). This meeting was arranged to discuss the results of the steam generator tube inspections performed during the 2004 refueling outage at the Vogtle Electric Generating Plant, Unit 2. A summary of the conference call is enclosed.
For your information, the NRC staff plans to keep TAC Nos. MC3046 and MC3047 open until we receive the results of the laboratory examination of the pulled tubes from the licensee.
If you have any questions regarding this matter, please contact me at (301) 415-1055.
Sincerely,
/RA/
Christopher Gratton, Sr. Project Manager Section 1 Project Directorate II Division of Licensing Project Management Office of Nuclear Reactor Regulation Docket Nos. 50-424 and 50-425
Enclosure:
Summary of Conference Call (ADAMS Accession No.: ML041430003) cc w/encl: See next page
ML041430003) cc w/encl: See next page ADAMS Accession No.: ML041660086 NRR-106 OFFICE PDII-1/PM PDII-1/LA (A)
EMCB/SC*
PDII-1/SC (A)
NAME CGratton DClarke ALund SCoffin DATE 6/10/04 6/10/04 5/13/04 6/10/04
DISTRIBUTION FOR VOGTLE ELECTRIC GENERATING PLANT, UNIT 2 -
SUMMARY
OF CONFERENCE CALL WITH SOUTHERN NUCLEAR OPERATING COMPANY REGARDING THE 2004 STEAM GENERATOR TUBE INSPECTION RESULTS (TAC NOS. MC3046 AND MC3047)
Dated: June 10, 2004 DISTRIBUTION:
PUBLIC PDII R/F RidsNrrDlpmLpdii (EHackett)
RidsNrrPMCGratton CHawes/DClarke RidsOgcRp RidsAcrsAcnwMailCenter RidsRgn2MailCenter (BBonser)
LLund EMurphy CKhan KKarwoski PKlein MMurphy GMakar CLauron JTerrell YDiaz BLee KGreen-Bates MLesser JNakoski/SCoffin
Enclosure CONFERENCE CALL
SUMMARY
2004 STEAM GENERATOR TUBE INSPECTIONS VOGTLE UNIT 2 On May 4, 2004, the NRC staff participated in a conference call with representatives of Vogtle Electric Generating Plant, Unit 2 (the licensee) to discuss their 2004 steam generator (SG) tube inspection results. The discussion topics included the SG tube inspection scope and the associated results. The call focused on the detection of circumferential indications at the expansion transition.
Vogtle Unit 2 has four Westinghouse model F SGs. Each SG contains 5,626 thermally treated Alloy 600 tubes. Each tube has a nominal outside diameter of 0.688-inch and a nominal wall thickness of 0.040-inch. The tubes were hydraulically expanded at both ends for the full length of the tubesheet and are supported by a number of stainless steel tube supports with quatrefoil shaped holes. The U-bend region of the tubes installed in rows 1 through 10 were thermally stress relieved after bending. The hot-leg temperature is approximately 617 F.
For the 2004 outage, the licensee planned on performing the following tube inspections in SGs 2 and 3:
Bobbin probe inspection of 100 percent of the tubes from tube-end to tube-end Rotating probe inspection (+Point' coil) of the hot-leg expansion transition region of 50 percent of the tubes from 3-inches above to 3-inches below the top of the tubesheet.
Rotating probe inspection (+Point' coil) of the U-bend region of 50 percent of the row 1 and 2 tubes Rotating probe inspection (+Point' coil) of the 100 percent of the hot-leg dents and dings with bobbin voltage amplitudes greater than 5 volts Rotating probe inspection (+Point' coil) of bobbin I-codes As a result of the identification of four circumferential indications at the hot-leg expansion transition at the top of the tubesheet, the licensee expanded their rotating probe examination at the hot-leg expansion transition region to include 100 percent of the tubes in SGs 2 and 3. As a result of this expansion, the licensee identified two additional tubes with circumferential indications at the expansion transition. All six circumferential indications initiated from the outside diameter of the tube.
To further characterize the nature of these six indications, the licensee performed ultrasonic testing (UT). Of the six indications, four were confirmed by UT to be present. For the two indications that were not confirmed by UT, the licensee could not rule out that the indications were below the threshold of detection for the UT equipment. As a result, all six tubes will be treated as flawed. The UT indicated that two of the flaws were multiple circumferential indications; whereas the other two flaws were single circumferential indications. Multiple circumferential indications were detected in the tubes in row 12 column 59 in SG 2 and row 11 column 65 in SG 3.
The indications were sized with the +Point' coil. Most of the indications did not extend more than 60-degrees around the tube circumference; however one did extend to 101-degrees. The deepest flaw was estimated to be 38 percent through-wall.
Given the identification of these circumferential indications, the licensee decided to perform a rotating probe inspection (+Point' coil) of the hot-leg expansion transition region of 20 percent of the tubes in SGs 1 and 4 from 3-inches above to 3-inches below the top of the tubesheet.
This 20 percent sample would be biased to encompass the regions where the circumferential indications were found in SGs 2 and 3. This includes a 20 tube by 20 tube box near the center of the tube bundle in which five of the six circumferential indications were found in SGs 2 and 3.
This sample also includes approximately 200 tubes around stay rods since the sixth indication was found in a tube near a stay rod. This sixth indication was not identified/confirmed during the UT inspection. The licensee indicated that sludge removal may be more difficult around the stay rod region. The remainder of the 20 percent sample of the hot-leg expansion transitions will be selected randomly. The inspections in SGs 1 and 4 were on-going at the time of the conference call. If circumferential indications are detected in this 20 percent sample, the scope will be expanded to include 100 percent of the hot-leg expansion transitions in the affected SG(s).
There is sludge at the top of the tubesheet in the Vogtle SGs; however, the sludge is characterized more as collars of deposits surrounding the tubes rather than a consistent height of material between the tubes. The average sludge height for SGs 2 and 3 was estimated to be approximately 1-inch, with a maximum sludge height of approximately 2.5-inches. The maximum sludge-height is only observed on a small number (1 or 2) tubes. Profiling of the sludge height was on-going for SGs 1 and 4. The sludge height for the tubes with circumferential indications was not readily available at the time of the call. The top of the tubesheet region at Vogtle is considered relatively clean.
Given the inspection results, the licensee is planning to remove two of these circumferential indications for destructive examination. The tubes will be examined by Westinghouse. The two tubes will include the largest indication and one of the smaller indications. The tubes will be cut below the second tube support. Rotating probe (+Point' coil) examinations were performed in the tubes to be pulled from the second tube support through the hot-leg tube end. No indications, other than those at the expansion transition, were identified.
The destructive examination results are intended to lend some insights into the cause and nature of these indications. Possible causes include (1) stress corrosion cracking as a result of the operating time and temperature and/or (2) stress corrosion cracking as a result of the inadvertent addition of sodium phosphate into the SGs in November 2002.
In response to axial indications found at the tube support plate elevations at Seabrook, a low frequency bobbin coil eddy current (EC) screening technique was used at Vogtle 2 to identify tubes that may have an EC offset similar to that observed at Seabrook. At Seabrook, several tubes were identified to have crack-like indications associated with this offset (refer to NRC Information Notice 2002-21, Axial Outside Diameter Cracking Affecting Thermally Treated Alloy 600 Steam Generator Tubing, dated June 25, 2002, and its supplement dated April 1, 2003, for additional details). As a result of applying this screening technique, one tube was identified with an offset in the cold-leg portion of the tube (but not on the hot-leg). The entire offset region in this tube was inspected with a rotating probe (+Point' coil), and no degradation was identified. In addition, one larger radii tube (row 40 column 48 in SG 2) was identified with no offset in the U-bend region. This tube was inspected with a bobbin coil and no degradation was identified. Given the absence of degradation, both tubes will be left in service.
As a result of the inspections, all six tubes with circumferential indications will be plugged and one tube will be plugged for wear at the anti-vibration bars.
At the end of the call, the NRC staff requested that the licensee keep the NRC staff informed of the results of their inspections in SGs 1 and 4 and of the results from their destructive examinations. The licensee was planning on notifying the industry of their inspection findings.
Following the May 4, 2004, conference call, the licensee informed the NRC staff that they detected circumferential indications in SGs 1 and 4 and expanded the expansion transition inspection to include 100 percent of the tubes. A total of three circumferential indications were detected during these inspections (two in SG 1 and one in SG 4). The size of the indications in SGs 1 and 4 were similar to the size of indications detected in SGs 2 and 3. In SG 1, tube R11C64 had a 68-degree, 31 percent through-wall, 0.27 volt (by +PointTM) circumferential indication. In SG 4, tube R11C50 had a 98-degree, 34 percent through-wall, 0.21 volt (by
+PointTM) circumferential indication; and tube R11C67 had a 56-degree, 34 percent through-wall, 0.34 volt (by +PointTM) circumferential indication. By contrast, the deepest indication in SGs 2 and 3 was 38 percent through-wall based on EC sizing. This indication was estimated to be 42 percent through-wall based on UT. The licensee indicated that a variety of different EC sizing techniques were applied to the flaws; however, at this point, the estimates made during the field analysis of the data are considered the best estimates. The circumferential indications in SGs 1 and 4 were located in tubes within a 20 tube by 20 tube box, as discussed above. The circumferential indications in all four SGs were plugged.
Vogtle Electric Generating Plant cc:
Mr. N.J. Stringfellow Manager, Licensing Southern Nuclear Operating Company, Inc.
P. O. Box 1295 Birmingham, Alabama 35201-1295 Mr. Skip Kitchens General Manager, Vogtle Electric Generating Plant Southern Nuclear Operating Company, Inc.
P. O. Box 1600 Waynesboro, Georgia 30830 Mr. J. B. Beasley, Jr.
Executive Vice President Southern Nuclear Operating Company, Inc.
P. O. Box 1295 Birmingham, Alabama 35201-1295 Steven M. Jackson Senior Engineer - Power Supply Municipal Electric Authority of Georgia 1470 Riveredge Parkway, NW.
Atlanta, Georgia 30328-4684 Mr. Reece McAlister Executive Secretary Georgia Public Service Commission 244 Washington St., S. W.
Atlanta, Ga. 30334 Harold Reheis, Director Department of Natural Resources 205 Butler Street, SE. Suite 1252 Atlanta, Georgia 30334 Attorney General Law Department 132 Judicial Building Atlanta, Georgia 30334 Mr. Laurence Bergen Oglethorpe Power Corporation 2100 East Exchange Place P. O. Box 1349 Tucker, Georgia 30085-1349 Arthur H. Domby, Esquire Troutman Sanders NationsBank Plaza 600 Peachtree Street, NE.
Suite 5200 Atlanta, Georgia 30308-2216 Resident Inspector Vogtle Plant 8805 River Road Waynesboro, Georgia 30830 Office of the County Commissioner Burke County Commission Waynesboro, Georgia 30830