ML120930296

Review of the 2011 Steam Generator Tube Inservice Inspection at Braidwood Station Unit 2

ML120930296
Person / Time
Site:	Braidwood
Issue date:	04/12/2012
From:	Mozafari B Plant Licensing Branch III
To:	Pacilio M Exelon Generation Co, Exelon Nuclear
Mozafari B
References
TAC ME7112
Download: ML120930296 (4)

Text

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 April 12, 2012 Mr. Michael J. Pacilio President and Chief Nuclear Officer Exelon Nuclear 4300 Winfield Road Warrenville,IL 60555

SUBJECT:

BRAIDWOOD STATION, UNIT NO.2 - REVIEW OF THE 2011 STEAM GENERATOR TUBE INSERVICE INSPECTIONS AT BRAIDWOOD STATION UNIT 2 (TAC NO. ME7112)

Dear Mr. Pacilio:

By letter dated August 10, 2011 (Agencywide Documents Access and Management System (ADAMS) Accession Number ML11227A037), Exelon Generation Company, LLC (the licensee) submitted information summarizing the results of the 2011 steam generator (SG) tube inspections at Braidwood Station Unit 2. These inspections were performed during the fifteenth refueling outage (A2R15). The licensee also provided some clarifying information concerning the 2011 inspections in a phone call on February 3, 2012. In addition to this report, the U.S. Nuclear Regulatory Commission staff summarized a conference call about the 2011 SG tube inspections at Braidwood Station Unit 2 in a letter dated September 22, 2011 (ADAMS Accession Number ML112590225).

If you have any questions regarding this matter, please contact me at (301) 415-2020.

Sincerely, ' ..

~>.~L~~11M-'

Brenda L. Mozafari, Senior Project Manager Plant Licensing Branch 111-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. STN 50-457

Enclosure:

Steam Generator Tube Inspection cc w/encl: Distribution via Listserv

REVIEW OF THE 2011 STEAM GENERATOR TUBE INSERVICE INSPECTIONS BRAIDWOOD STATION UNIT 2 DOCKET NO. 50-457 By letter dated August 10, 2011 (Agencywide Documents Access and Management System (ADAMS) Accession Number ML11227A037), Exelon Generation Company, LLC (the licensee) submitted information summarizing the results of the 2011 steam generator (SG) tube inspections at Braidwood Station Unit 2. These inspections were performed during the fifteenth refueling outage (A2R15). The licensee also provided some clarifying information concerning the 2011 inspections in a phone call on February 3, 2012. In addition to this report, the U.S. Nuclear Regulatory Commission staff summarized a conference call about the 2011 SG tube inspections at Braidwood Station Unit 2 in a letter dated September 22, 2011 (ADAMS Accession Number ML112590225).

Braidwood Station Unit 2 has four Westinghouse Model D5 SGs. There are 4570 thermally treated Alloy 600 tubes in each SG, with an outside diameter of 0.750 inches and a nominal wall thickness of 0.043 inches. The tubes are hydraulically expanded for the full depth of the tubesheet at each end and are welded to the tubesheet at the bottom of each expansion. The tubes are supported by a number of Type 405 stainless steel supports with quatrefoil shaped holes.

The licensee provided the scope, extent, methods, and results of their SG tube inspections in the documents referenced above. In addition, the licensee described corrective actions, such as tube plugging, taken in response to the inspection findings. The tubes in all four SGs were inspected during this refueling outage.

After reviewing the information provided by the licensee, the staff has the following comments/observations:

1. The modes of tube degradation found during A2R 15 were anti-vibration bar wear, pre-heater tube support plate wear, secondary side foreign object wear, and axial outside diameter stress corrosion cracking (SCC).

2. The licensee performed visual inspections of the secondary side moisture separator region in SGs 2B during A2R15. This was a follow-up inspection based on erosion of the moisture separator tangential nozzles, down comer barrels, and swirl vanes being Identified during A2R13 (2008) and A2R14 (2009).

UT measurements were taken of the eroded areas, with an emphasis on re inspection of the eroded areas identified in SG 2B during the A2R13 and A2R14 inspections. While continued erosion of components in SG 2B was identified, no indications of through-wall erosion were identified. The bounding wear measurement in the 2B SG showed a maximum wall loss of 51 percent, as compared to the original manufacturing nominal value. An analysis was performed by the licensee that determined that significant margin remained in the eroded areas before the erosion would penetrate through-wall and affect SG performance or possibly generate loose parts. The erosion was not projected to penetrate through-wall, create loose parts, or impact SG performance prior to the next inspection of the region. Monitoring of the condition is planned over Enclosure

-2 subsequent operating cycles in order to develop a degradation growth rate and take corrective actions if they become necessary.

3. In the February 3, 2012, phone call, the licensee clarified the following:

a. The "corner" preheater expansion region of the 2nd tube support plate in SG A was visually inspected and therefore, no +PoinhM eddy current inspection of this region was performed.

b. The 39 tubes with manufacturing artifacts were similar in nature to the artifacts identified in Information Notice 2010-21, "Crack-Like Indication in the U-Bend Region of a Thermally Treated Alloy 600 Steam Generator Tube." The artifacts were a dimensional change in the tube diameter at the tangent point that was created during tube bending. The tubes were inspected with a +PoinhM probe at the tangent point locations, and no indications of SCC were found.

c. There were potential loose part (PLP) signals noted at some of the foreign object wear indications discussed in Section 5.1.2 of the August 10, 2011, letter. If a tube had a PLP signal and was inaccessible for a visual inspection, then the tube was stabilized and plugged.

d. At the start of operating cycle 16, the SGs at Braidwood Unit 2 have accumulated 224.11 effective full power months since the first refueling outage after SG installation.

4. In the NRC staff's conference call summary, dated September 22, 2011 (ADAMS Accession Number ML112590225), three hot-leg single axial indications were listed as being found in the tube located in row 2 column 35 (R2C35) of SG D. The summary also stated that the straight leg portion of tube R2C35 did not exhibit an absolute signal offset with respect to the u-bend. After the conference call summary was issued, the licensee informed the NRC staff that the tube in R2C35 did exhibit an absolute signal offset with respect to the u-bend. There was only one tube identified as having SCC.

Based on a review of the information provided by the licensee, the staff concludes that the licensee provided the information required by their technical specifications. The SG tube inspections at Braidwood Station Unit 2 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.

April 12, 2012 Mr. Michael J. Pacilio President and Chief Nuclear Officer Exelon Nuclear 4300 Winfield Road Warrenville, I L 60555 SUB.IECT: BRAIDWOOD STATION, UNIT NO.2 - REVIEW OF THE 2011 STEAM GENERATOR TUBE INSERVICE INSPECTIONS AT BRAIDWOOD STATION UNIT 2 (TAC NO.

ME7112)

Dear Mr. Pacilio:

By letter dated August 10, 2011 (Agencywide Documents Access and Management System (ADAMS)

Accession Number ML11227A037), Exelon Generation Company, LLC (the licensee) submitted information summarizing the results of the 2011 steam generator (SG) tube inspections at Braidwood Station Unit 2. These inspections were performed during the fifteenth refueling outage (A2R15). The licensee also provided some clarifying information concerning the 2011 inspections in a phone call on February 3, 2012. In addition to this report, the U.S. Nuclear Regulatory Commission staff summarized a conference call about the 2011 SG tube inspections at Braidwood Station Unit 2 in a letter dated September 22,2011 (ADAMS Accession Number ML112590225).

If you have any questions regarding this matter, please contact me at (301) 415-2020.

Sincerely, IRA!

Brenda L. Mozafari, Senior Project Manager Plant Licensing Branch 111-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. STN 50-457

Enclosure:

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