ML101820184

Evaluation of 2009 (Cycle 24) Steam Generator Tube Inspections

ML101820184
Person / Time
Site:	Oconee
Issue date:	07/07/2010
From:	Stang J Plant Licensing Branch II
To:	Baxter D Duke Energy Carolinas
Stang, JF, NRR/DORL/LPL2-1, 415-1345
References
TAC ME2219
Download: ML101820184 (3)

Text

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 July 7, 2010 Mr. Dave Baxter Vice President, Oconee Site Duke Energy Carolinas, LLC 7800 Rochester Highway Seneca, SC 29672

SUBJECT:

OCONEE NUCLEAR STATION, UNIT 3 (OCONEE 3), EVALUATION OF 2009 (CYCLE 24) STEAM GENERATOR (SG) TUBE INSPECTIONS (TAC NO.

ME2219)

Dear Mr. Baxter:

By letter dated August 14, 2009, Duke Energy Carolinas, LLC (the licensee), submitted information pertaining to its 2009 SG tube inspections at Oconee 3, during the Cycle 24 refueling outage.

The U.S Nuclear Regulatory Commission (NRC) staff has completed its review of these reports and concludes that the licensee provided the information required by their technical specifications and that no additional follow-up is required at this time. The NRC staffs review of the reports is enclosed.

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~ng, Senior Project Manager Plant Licensing Branch 11-1 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-287

Enclosure:

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SUMMARY

OF REVIEW BY THE OFFICE OF NUCLEAR REACTOR REGULATION OCONEE NUCLEAR STATION, UNIT 3 EVALUATION OF THE STEAM GENERATOR INSPECTIONS PERFORMED DURING THE 2009 REFUELING OUTAGE DOCKET NO. 50-287 By letter dated August 14, 2009 (Agencywide Documents Access and Management System, Accession No. ML092330195), Duke Energy Carolinas, LLC (Duke, the licensee), submitted information summarizing the results of the 2009 steam generator (SG) tube inspections at Oconee Nuclear Station, Unit 3 (Oconee 3) that were performed during refueling outage 24 (RFO 24).

Oconee 3 is a two-loop pressurized-water reactor with replacement once-through steam generators (ROTSGs) manufactured by Babcock & Wilcox (B&W), Canada. The Oconee 3 ROTSGs were installed during the fall 2004 refueling outage. The ROTSGs contain 15,631 thermally treated Alloy 690 tubes that have been hydraulically expanded into the tubesheet to a depth of 13 inches. There are 15 Type 410 stainless steel tube support plates (TSP) of trifoil broach design; however, there are some round drilled openings at the 14th TSP. The inspection performed in spring 2009 was the third inservice inspection of the ROTSGs.

The first inservice inspection of the ROTSGs at Oconee 3 (spring 2006) revealed widespread wear degradation of the tubing at TSP locations. Oconee 1 and 2 have also experienced this widespread tube wear degradation at TSP locations.

As a result of the 2009 inspections, three tubes were plugged in ROTSG 3A and eight tubes were plugged in ROTSG 3B. Four of the tubes were plugged due to wear (3 in ROTSG 3A (R105C109, R139C70, R145C22) and 1 in ROTSG 3B (R71C3)). One tube in ROTSG 3B (R114C99) was plugged due to an obstruction and the six tubes (R113C99, R113C100, R114C98, R114C100, R115C98, and R115C99) surrounding the obstructed tUbe were preventively plugged and stabilized. The obstruction was caused by a foreign object. Based on visual inspection, the object appears to be a small bearing (likely a roller bearing used in the eddy current snorkel support assembly). Efforts to dislodge the foreign object were unsuccessful. The following acronyms were used in the licensee's report: OBS (obstructed tube), ROB (retest obstructed tube), and LAR (lead analyst review).

Based on a review of the information provided, the Nuclear Regulatory Commission (NRC) staff concludes that the licensee provided the information required by their Technical Specifications.

In addition, the NRC staff concludes that there are no technical issues that warrant follow-up action 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.

Enclosure

• .. ML101820184 'Memo submitted by Tech Staff dated OFFICE NRRlLPL2-1/PM NRRlLPL2-1/LA NRRlDCI/CSGB/BC NRRlLPL2-1/BC NRRlLPL2-1/PM NAME JStang MO'Brien RTaylor' GKulesa JStang DATE 7/7/10 7/7/10 05/13/10 717110 7/7/10