ML063530739
| ML063530739 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 01/03/2007 |
| From: | Olshan L NRC/NRR/ADRO/DORL/LPLII-1 |
| To: | Brandi Hamilton Duke Power Co |
| Olshan L N, NRR/DORL, 415-1419 | |
| References | |
| TAC MD3388 | |
| Download: ML063530739 (5) | |
Text
January 3, 2007 Mr. Bruce H. Hamilton Vice President, Oconee Site Duke Power Company LLC 7800 Rochester Highway Seneca, SC 29672
SUBJECT:
SUMMARY
OF OCTOBER 26, 2006, CONFERENCE CALL REGARDING FALL 2006 STEAM GENERATOR TUBE INSPECTIONS AT OCONEE NUCLEAR STATION, UNIT 1 (OCONEE)
Dear Mr. Hamilton:
On October 26, 2006, we participated in a conference call with your staff to discuss the scope, results, and status of steam generator (SG) tube inspections being conducted at that time at Oconee Unit 1 (fall 2006 Refueling Outage). A summary of the call is provided in. Enclosure 2 contains information provided by the licensee prior to the call.
Sincerely,
/RA/
Leonard N. Olshan, Project Manager Plant Licensing Branch II-1 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-269
Enclosures:
- 1. Conference Call Summary
- 2. Inspection Discussion Points cc w/encls: See next page
Mr. Bruce H. Hamilton Vice President, Oconee Site Duke Power Company LLC 7800 Rochester Highway Seneca, SC 29672
SUBJECT:
SUMMARY
OF OCTOBER 26, 2006, CONFERENCE CALL REGARDING FALL 2006 STEAM GENERATOR TUBE INSPECTIONS AT OCONEE NUCLEAR STATION, UNIT 1 (OCONEE)
Dear Mr. Hamilton:
On October 26, 2006, we participated in a conference call with your staff to discuss the scope, results, and status of steam generator (SG) tube inspections being conducted at that time at Oconee Unit 1 (fall 2006 Refueling Outage). A summary of the call is provided in. Enclosure 2 contains information provided by the licensee prior to the call.
Sincerely,
/RA/
Leonard N. Olshan, Project Manager Plant Licensing Branch II-1 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-269
Enclosures:
- 1. Conference Call Summary
- 2. Inspection Discussion Points cc w/encls: See next page DISTRIBUTION:
Public RidsOgcRp LPL2-1 R/F RidsAcrsAcnwMailCenter RidsNrrDorlLpl2-1 (Emarinos) RidsRgn2MailCenter (MErnstes)
RidsNrrPMLOlshan RidsNrrLAMOBrien Accession Number: Package ML070080336, Ltr. ML063530739, Enclosure 2 ML070050212 OFFICE NRR/LPL2-1/PM NRR/LPL2-1/LA NRR/LPL2-1/BC NAME LOlshan:me MOBrien EMarinos DATE 1 /03 /2007 12/28 /2006 1 /03 /2006 OFFICIAL RECORD COPY
OCTOBER 26, 2006,CONFERENCE CALL
SUMMARY
REGARDING FALL 2006 STEAM GENERATOR INSPECTIONS DUKE POWER COMPANY, LLC OCONEE NUCLEAR STATION, UNIT 1 DOCKET NO. 50-269 Introduction and Background On October 26 2006, the Nuclear Regulatory Commission (NRC) staff participated in a conference call with Duke Power Company, LLC (the licensee), to discuss the scope, results, and status of steam generator tube inspections being conducted during the fall 2006 refueling outage at Oconee Nuclear Station, Unit 1 (Oconee Unit 1).
Oconee Unit 1 is a two-loop pressurized water reactor with once-through steam generators (OTSGs) manufactured by Babcock & Wilcox, Canada. The Oconee Unit 1 OTSGs are replacement OTSGs installed during a refueling outage in the fall of 2003. The ongoing inspections at Oconee Unit 1 are the second inservice inspections of the replacement OTSGs at this unit.
A major point of interest to the NRC staff going into the call was the state of tube wear at Oconee Unit 1. The first inservice inspection of the Oconee 1 replacement OTSGs in the spring of 2005 revealed unexpected, widespread wear degradation of the tubing at tube support plate locations. The first inservice inspections of the replacement OTSGs at Oconee Units 2 and 3 in the fall of 2005 and spring of 2006, respectively, also revealed widespread wear degradation, although less prevalent than at Oconee Unit 1.
Call Summary In advance of the phone call, the licensee provided a written summary (Enclosure 2 of this letter) of its inspection program, status, and results to date. This summary addressed all discussion points requested by the NRC staff prior to the phone call. During the phone call, the licensee walked the NRC staff through the summary material.
The licensee had completed 95 percent of its planned inspections in the 1A OTSG and 99 percent in the 1B OTSG at the time of the phone call. The inspection program includes a bobbin coil inspection of all approximately 15,600 tubes in each OTSG. Approximately 60 percent of the tubes are also being inspected with an X-Probe. In addition, X-Probe inspections are being performed for all locations where the bobbin coil detected indications >20 percent through wall (TW), new indications >10 percent TW, and indications which have grown >10 percent TW since the previous inspection.
As was observed previously during the first inservice inspection, widespread wear degradation was observed during this inspection at the tube support plates (TSPs), particularly TSPs 8 through 14. The percentage of tubes with wear indications is currently 28 percent in 1A OTSG and 24 percent in 1B OTSG. This percentage is more than double that observed during the first inservice inspection. Apart from the wear degradation, no other types of degradation were observed during the inspection.
A total of 15 indications had measured wear depths > 40 percent TW, with the deepest indication measuring 49 percent TW. This compares with the first inservice inspection when 5 indications had measured wear depths > 40 percent TW with the deepest indication measuring 42 percent TW. The average wear depth for all indications was 9 percent in both OTSGs. The average wear depth for new indications was 8 percent and 7 percent in 1A OTSG and 1B OTSG, respectively.
New indications ranged in depth to as much as 40 percent TW. The maximum growth rate (per effective full power year (EFPY)) for indications left in service following the first inservice inspection was about 29 percent TW (or about 40 percent TW for the entire operating cycle),
and the average growth rate was about 2 to 3 percent TW (per EFPY). During the first inservice inspection, the licensee plugged all tubes with indications equal to or deeper than 28 percent TW.
During the phone call, the licensee stated that the maximum allowable depth consistent with satisfying the 3 times normal operating pressure burst criterion (i.e., the structural limit) is 78 percent TW for the tapered wear scar geometry being exhibited at the Oconee units. Based upon the inspection results to date, the licensee is planning to plug all tubes with indications >
35 percent TW depth. This is less than the technical specification limit of 40 percent TW, but greater than the 28 percent limit implemented during the first inservice inspection. The 35 percent limit was derived from the structural limit by subtracting the maximum observed growth rate and a Monte Carlo summation of eddy current depth measurement, burst equation, and material property uncertainties.
Note, the material from the licensee provided in Enclosure 2 of this letter, refers to a condition monitoring depth limit of 73 percent TW. This number presumably reflects an allowance for eddy current measurement error whereas the above 78 percent structural limit number does not.
The licensee met with the NRC staff on April 10, 2006 (ML061100211), to discuss the status of its ongoing program to identify the contributing causes of the wear degradation at the Oconee units and potential measures to mitigate future wear. This program includes, in part, the installation of accelerometers on the OTSG upper channel head and steam line and installing pressure transducers through various inspection port covers at each of the Oconee units to acquire data on excitation sources which may be contributing to the wear problem. During the phone call on October 26, 2006, the licensee confirmed that this instrumentation package was being installed at Unit 1.
Oconee Nuclear Station, Units 1, 2, and 3 cc:
Mr. Bruce H. Hamilton Vice President, Oconee Site Duke Power Company LLC 7800 Rochester Highway Seneca, SC 29672 Ms. Lisa F. Vaughn Associate General Counsel and Managing Attorney Duke Energy Carolinas, LLC 526 South Church Street - EC07H Charlotte, North Carolina 28202 Manager, LIS NUS Corporation 2650 McCormick Dr., 3rd Floor Clearwater, FL 34619-1035 Senior Resident Inspector U.S. Nuclear Regulatory Commission 7812B Rochester Highway Seneca, SC 29672 Mr. Henry Porter, Director Division of Radioactive Waste Management Bureau of Land and Waste Management Dept. of Health and Env. Control 2600 Bull St.
Columbia, SC 29201-1708 Mr. Michael A. Schoppman Framatome ANP 1911 North Ft. Myer Dr.
Suite 705 Rosslyn, VA 22209 Mr. B. G. Davenport Regulatory Compliance Manager Oconee Nuclear Site Duke Energy Corporation ON03RC 7800 Rochester Highway Seneca, SC 29672 Mr. Leonard G. Green Assistant Attorney General NC Department of Justice P.O. Box 629 Raleigh, NC 27602 Mr. R. L. Gill, Jr.
Manager - Nuclear Regulatory Issues and Industry Affairs Duke Power Company LLC 526 S. Church St.
Mail Stop EC05P Charlotte, NC 28202 Division of Radiation Protection NC Dept of Environment, Health, & Natural Resources 3825 Barrett Dr.
Raleigh, NC 27609-7721 Mr. Peter R. Harden, IV VP-Customer Relations and Sales Westinghouse Electric Company 6000 Fairview Road 12th Floor Charlotte, NC 28210 Mr. Henry Barron Group Vice President, Nuclear Generation and Chief Nuclear Officer P.O. Box 1006-EC07H Charlotte, NC 28201-1006 Mr. Charles Brinkman Director, Washington Operations Westinghouse Electric Company 12300 Twinbrook Parkway, Suite 330 Rockville, MD 20852 Ms. Kathryn B. Nolan Senior Counsel Duke Energy Carolinas, LLC 526 South Church Street - EC07H Charlotte, NC 28202