ML16053A219
| ML16053A219 | |
| Person / Time | |
|---|---|
| Site: | Wolf Creek  |
| Issue date: | 02/24/2016 |
| From: | Lyon C Plant Licensing Branch IV |
| To: | Heflin A Wolf Creek |
| Lyon C | |
| References | |
| CAC MF7016 | |
| Download: ML16053A219 (4) | |
Text
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 FEbnEry 24, 2016 Mr. Adam C. Heflin President, Chief Executive Officer, and Chief Nuclear Officer Wolf Creek Nuclear Operating Corporation Post Office Box 411 Burlington, KS 66839
SUBJECT:
WOLF CREEK GENERATING STATION - REVIEW OF THE 2015 STEAM GENERATOR TUBE INSERVICE INSPECTION REPORT (Cf.C NO. MF7016)
Dear Mr. Heflin:
By letter to the U.S. Nuclear Regulatory Commission (NRC) dated October 20, 2015, Wolf Creek Nuclear Operating Corporation (the licensee) submitted its inspection results for the 19th steam generator tube inservice inspection at Wolf Creek Generating Station, which was conducted during refueling outage 20. Your report was submitted in accordance with Technical Specification (TS) 5.6.10, "Steam Generator Tube Inspection Report."
Based on its review, the NRC staff concludes that the licensee has provided the information required by TS 5.6.10. A summary of the NRC staff's review is enclosed. If you have any questions, please contact me at 301-415-2296 or via e-mail at Fred.Lyon@nrc.gov.
Docket No. 50-482
Enclosure:
As.stated cc w/encl: Distribution via Listserv Sincerely, Carl F. Lyon, Project Manager Plant Licensing Branch IV-1 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation
SUMMARY
OF THE REVIEW OF THE 2015 REFUELING OUTAGE 20 STEAM GENERATOR TUBE INSERVICE INSPECTION REPORT WOLF CREEK NUCLEAR OPERATING CORPORATION WOLF CREEK GENERATING STATION DOCKET NO. 50-482 By letter dated October 20, 2015 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML15300A335), Wolf Creek Nuclear Operating Corporation (the licensee), submitted information summarizing the results of the 2015 steam generator (SG) tube.
inspections performed at Wolf Creek Generating Station (Wolf Creek) during refueling outage 20 (RFO 20).
Wolf Creek 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 inches and a nominal wall thickness of 0.040 inches. The tubes are supported by stainless steel tube support plates (TSP) with quatrefoil-shaped holes and V-shaped chrome-plated Alloy 600 anti-vibration bars (AVB).
The licensee provided the scope, extent, methods, and results of its SG tube inspections in the documents referenced above. lri addition, the licensee described corrective actions, such as tube plugging, taken in response to the inspection findings.
The licensee clarified several aspects of its spring 2015 inspections in January 2016 (ADAMS Accession No. ML16006A368) as follows:
A group of 15 historic indications above the top of the tubesheet (TTS) in SG C are monitored during each inspection. These indications *are a.II on row 1 tubes (between columns 4 and 20) at an elevation of approximately 15 inches above the TTS on the cold-leg side. Since these indications are all on tubes in the tube lane and at the same elevation, these indications are believed to be due to prior secondary side cleanings, where tooling wore on the tubes along the tube lane.
The indications are being tracked in history and are not growing.
A total of 21 tubes throughout the four SGs contain volumetric indications near the TTS, which are also monitored during each inspection and are not growing.
The distribution of these indications is typical of positions where foreign objects have been found to interact with the tubes. None of these indications are associated with a current loose part (LP) signal, but it is assumed that the indications are the result of wear from a prior LP.
One volumetric indication was identified approximately 0. 78 inches below the TTS in the tube at row 27, column 97 in SG D during RFO 20. The indication is not changing. The licensee reported the measured percent through-wall depths of the indication for RFO 13, 15, 17, 18, 19, and 20 as 9 percent, 15 percent, 17 percent, 15 percent, 16 percent, and 15 percent, respectively. Since the
- Enclosure indication is slightly below the TTS, it is believed to be a geometric anomaly that could have occurred during manufacturing (e.g., expansion into a burr or undercut remaining from the tubesheet drilling process). Additional discussion can be found in the licensee's letter dated July 14, 2005 (ADAMS Accession No. ML052080042).
The number of AVB, TSP (including flow distribution baffle (FOB)), and LP wear indications in the four SGs are summarized in the table below. The licensee indicated that the total indications and tubes in the table are for all indications reported. The licensee noted that a few tubes have more than one type of indication in the same tube, such that the total indications and tubes may differ from the sum of the individual mechanisms.
AVB TSP (includinq FOB)
LP Indications Tubes Indications Tubes Indications Tubes SGA 704 307 1
1 2
2 SG B 1015 440 13 7
2 2
SGC 638 283 6
6 15 15 SGD 1147 445 25 13 2
2 In addition to the indications in the table above, there were 15 indications in 15 tubes in SG C associated with previous wear from secondary side cleaning.
A single circumferential primary water stress-corrosion cracking indication was detected in SG A at row 20, column 102, 3.91 inches below the TTS hot leg. The indication was associated with a 4 Volt bulge anomaly, which was not previously identified or tracked since the bulge reporting threshold was 18 Volts.
A site-specific U-bend fatigue analysis was performed and identified 17 tubes that required remedial action. These tubes indicated a fatigue usage factor greater than 1.0 over a 60-year plant life using a calculation methodology consistent with the methods used to satisfy U.S. Nuclear Regulatory Commission Bulletin No. 88-02, "Rapidly Propagating Fatigue Cracks In Steam Generator Tubes," dated February 5, 1988 (ADAMS Accession No. ML031220043),
requirements*for steam generators with carbon steel drilled hole TSPs. All 17 tubes were removed from service by tube plugging with a mecha'nical plug on the hot leg and a sentinel plug on the cold leg.
An area of primary channel head wastage, which was first reported during RFO 19, due to a cladding breach in SG A was determined to be acceptable for continued operation. Ultrasonic testing during RFO 20 indicated no flaw growth.
Based on a review of the information provided, the NRC staff concludes that the licensee provided the information required by its technical specifications. In addition, the staff concludes that there are no technical issues that warrant follow-up actions at this time, since the inspections appear to be consistent with the objective of detecting potential tube degradation and the inspection results appear to be consistent with industry operating experience at similarly designed and operated units.
ML16053A219 OFFICE NRR/DORL/LPL4-1 /PM N RR/DORL/LPL4-1 /LA NAME FL yon JBurkhardt DATE 02/23/16 02/23/16 OFFICE N RR/DORL/LPL4-1 /BC N RR/DORL/LPL4-*1 /PM NAME RPascarelli FL yon DATE 02/23/16 02/24/16