ML072000367

Summary of Conference Call with Diablo, Unit 1, Regarding Their 2007 Steam Generator Tube Inspections (TAC No. MD5549

ML072000367
Person / Time
Site:	Diablo Canyon
Issue date:	07/19/2007
From:	Allen Hiser NRC/NRR/ADES/DCI
To:	Hiltz T NRC/NRR/ADRO/DORL/LPLIV
Burke, J P, NRR/DCI/CSGB, 415-1529
Shared Package
ML072000353	List: ML072000367 ML072000405
References
TAC MD5549
Download: ML072000367 (5)

Text

July 19, 2007 MEMORANDUM TO: Thomas G. Hiltz, Chief Plant Licensing Branch IV Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation FROM: Allen L. Hiser, Jr., Chief /RA/

Steam Generator Tube Integrity and Chemical Engineering Branch Division of Component Integrity Office of Nuclear Reactor Regulation

SUMMARY

OF CONFERENCE CALL WITH DIABLO CANYON UNIT 1 REGARDING THEIR 2007 STEAM GENERATOR TUBE INSPECTIONS (TAC NO. MD5549)

On May 15, 2007, the staff of the Steam Generator Tube Integrity and Chemical Engineering Branch (CSGB), Division of Component Integrity (DCI), Office of Nuclear Reactor Regulation, participated in a conference call to discuss the 2007 steam generator tube inspections performed at Diablo Canyon Unit 1 during their fourteenth refueling outage (1R14). To facilitate this conference call, the licensee provided a written summary of the scope and results of their inspection. Enclosed is a summary of the conference call. We ask that you make the enclosed summary, along with the written material provided by the licensee, publicly available.

The materials provided by the licensee are attached to the enclosed summary.

Please include myself, John Burke, and Ken Karwoski on distribution for the final document.

Please include me on concurrence only if you have made significant changes to the enclosed summary.

CSGB formally reviews all steam generator inspection summary reports submitted by licensees in accordance with the plants technical specification requirements. The licensees typically submit these summary reports within one year of the completion of the steam generator inspections. Therefore, please provide the report and a work request to me when it is submitted. The process for handling our review of steam generator inspection summary reports as well as the steam generator conference calls is outlined in the September 30, 2002, memo from Richard J. Barrett and John A. Zwolinski to Brian W. Sheron (ML022740514).

We appreciate your support in this matter, and this completes our efforts under the subject TAC.

Docket No.: 50-275

Enclosure:

Conference Call Summary CONTACT: John P. Burke, DCI/CSGB (301) 415-1529

July 19, 2007 MEMORANDUM TO: Thomas G. Hiltz, Chief Plant Licensing Branch IV Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation FROM: Allen L. Hiser, Jr., Chief /RA/

Steam Generator Tube Integrity and Chemical Engineering Branch Division of Component Integrity Office of Nuclear Reactor Regulation

SUMMARY

OF CONFERENCE CALL WITH DIABLO CANYON UNIT 1 REGARDING THEIR 2007 STEAM GENERATOR TUBE INSPECTIONS (TAC NO. MD5549)

On May 15, 2007, the staff of the Steam Generator Tube Integrity and Chemical Engineering Branch (CSGB), Division of Component Integrity (DCI), Office of Nuclear Reactor Regulation, participated in a conference call to discuss the 2007 steam generator tube inspections performed at Diablo Canyon Unit 1 during their fourteenth refueling outage (1R14). To facilitate this conference call, the licensee provided a written summary of the scope and results of their inspection. Enclosed is a summary of the conference call. We ask that you make the enclosed summary, along with the written material provided by the licensee, publicly available.

The materials provided by the licensee are attached to the enclosed summary.

Please include myself, John Burke, and Ken Karwoski on distribution for the final document.

Please include me on concurrence only if you have made significant changes to the enclosed summary.

CSGB formally reviews all steam generator inspection summary reports submitted by licensees in accordance with the plants technical specification requirements. The licensees typically submit these summary reports within one year of the completion of the steam generator inspections. Therefore, please provide the report and a work request to me when it is submitted. The process for handling our review of steam generator inspection summary reports as well as the steam generator conference calls is outlined in the September 30, 2002, memo from Richard J. Barrett and John A. Zwolinski to Brian W. Sheron (ML022740514).

We appreciate your support in this matter, and this completes our efforts under the subject TAC.

Docket No.: 50-275

Enclosure:

Conference Call Summary CONTACT: John P. Burke, DCI/CSGB (301) 415-1529 DISTRIBUTION:

DCI/ RF AWang EMurphy YDiaz-Castillo MYoder AJohnson WJones AHiser KKarwoski GMakar PKlein LMiller JBurke ADAMS PACKAGE ACCESSION NO.: ML072000353 OFFICE DCI/CSGB NRR/DCI DCI/CSGB NAME JBurke KKarwoski AHiser DATE 07/12 /07 07/12 /07 07/19/07 OFFICIAL RECORD COPY

MAY 15, 2007 CONFERENCE CALL

SUMMARY

STEAM GENERATOR TUBE INSPECTIONS DIABLO CANYON UNIT 1 DOCKET NO. 50-275 On May 15, 2007 the Nuclear Regulatory Commission staff participated in a conference call with Diablo Canyon Unit 1 representatives regarding their 2007 steam generator (SG) tube inspections. A summary of the information discussed during the call is provided below.

The four steam generators at Diablo Canyon Unit 1 are Westinghouse model 51. Each steam generator contains approximately 3400 mill annealed Alloy 600 tubes. Each tube has a nominal outside diameter of 0.875-inch and a nominal wall thickness of 0.050-inch. Each tube is roll-expanded for approximately 2.75 inches from the bottom of the tubesheet, and is secured into the remaining portion of the tubesheet by the Westinghouse Explosive Tube Expansion (WEXTEX) process. The tubesheet is approximately 21 inches thick and each tube is expanded for essentially the full thickness of the tubesheet. Each steam generator contains seven carbon steel tube support plates with drilled holes through which the tubes pass. All four steam generators are scheduled to be replaced during the next refueling outage in 2009.

In addition to a depth-based tube repair criteria, the licensee is authorized to apply the voltage-based tube repair criteria for predominantly axially-oriented outside diameter stress corrosion cracking (ODSCC) within the tube support plates. The licensee is also authorized to implement an alternate repair criteria for primary water stress corrosion cracking (PWSCC) indications at the tube support plate elevations and to leave certain flaws within the tubesheet region in service, provided they satisfy the W* repair criterion.

Prior to the call the licensee was provided with discussion points to help facilitate the phone conference. In support of the phone call, the licensee provided the attached document that provided inspection status as of May 15, 2007 (See Attachment ). At the time of the call, the eddy current inspections for Diablo Canyon Unit 1 were complete and repairs (tube plugging) were in progress. No unusual degradation or unexpected conditions were detected during the inspections. Most of the new indications were less than 0.5 volts Additional clarifying information or information not included in the Attachment provided by the licensee is summarized below:

C Acronyms used by the licensee in the material they provided include:

SG (steam generator), HTS (hotleg tubesheet), TSP (tube support plate), AVB (antivibration bar), SCC (stress corrosion cracking), DSI (distorted support indication), CLT (cold leg thinning), AONDB (axial ODSCC not detectable by bobbin), ET (eddy current testing), TTS (top of tubesheet), ARC (alternate repair criteria), ID (inside diameter), OD (outside diameter), DNT (dent), SAI (single axial indication), SPR (support plate residual), NDD (no detectable degradation), DIS (distorted ID support plate bobbin signal).

ENCLOSURE

C The amount of primary to secondary leakage observed during cycle 14, just completed, was very small and was similar to that observed during prior cycles.

C A deviation from Electric Power Research Institute guidelines for secondary water chemistry has existed for many years.

C No additional indications were found in the expanded scope examinations performed in SG 1-1 and 1-3 at dented TSPs.

C Approximately 16 cold leg thinning indications that were greater than 1.5 volts were re-inspected with a rotating probe. There were no unusual results. There were 11 new cold leg thinning indications identified this outage and these were inspected with a rotating probe. The total population of tubes with known cold leg thinning is approximately 171.

C All crack-like indications not covered by an Alternate Repair Criteria (ARC) are plugged.

C In Table 2, the DIS Overcall Rate should be 94% since two of the 32 DIS indications in less than 2 volt dents were confirmed as SAIs. The DIS overcall rate is typical.

C In Table 2, the axial PWSCC (New) row should indicate that there were 2 indications in steam generator 1-1 and none in steam generator 1-3.

C In Table 2, there were a total of 13 circumferential ODSCC indications.

C Of the 219 axial PWSCC indications that were present since the prior outage, the worst underprediction in the burst pressure (from the projections based on the last inspection) was only approximately 300 pounds per square inch (psig).

C The number of axial oriented ODSCC indications at the TSPs was less than the projections from the last inspection.

C The axial ODSCC indication in the sludge pile was approximately one-inch above the TTS. The sludge pile extends to approximately 2-inches above the TTS.

The sludge pile is considered small. This is the first time that an indication was found in the sludge pile. The indication was found with the rotating probe.

The licensee concluded that this was not a free span crack based on the location and the number of rotating probe exams performed in the free span region (as a result of indications at tube supports (i.e., 2-inches above and below the support),

the free span ding sampling program, and the inspection of other bobbin indications in the free span region).

C All of the volumetric OD indications were located at the TSP elevations.

All indications were at the lower TSPs and associated with bobbin indications.

The indications were attributed to intergranular attack or closely spaced axial ODSCC indications.

C The performance criteria associated with the steam line break and feedwater line break differential pressures are 3367 psig and 3790 psig, respectively (i.e., 1.4 times the differential pressure). The performance criteria associated with three times the normal operating differential pressure is 4473 psig.

C In Table 3, the projected (i.e., 2009) burst pressure for the tube in row 34 column 53 in steam generator 1-2 was 3582 psig based on the Argonne National Laboratory burst pressure model. This tube was plugged. The burst pressure for this indication (in the as-found 2007 condition) was slightly less than the projected burst pressure (based on the projection from the prior inspection in 2005).

C The axial indications in the sludge pile and at the TTS were small so the flaw dimensions were not profiled.

C All circumferential indications were considered small (i.e., less than the threshold value for in-situ pressure testing).

The staff did not identify any issues that warranted follow-up action at this time; however, the staff asked to be notified in the event that any unusual conditions were detected during the remainder of the outage.