DCL-10-149, Response to NRC Request for Additional Information Regarding the 180-Day Steam Generator Report for Fifteenth Refueling Outage

Response to NRC Request for Additional Information Regarding the 180-Day Steam Generator Report for Fifteenth Refueling Outage

ML103300051
Person / Time
Site:	Diablo Canyon
Issue date:	11/24/2010
From:	Becker J Pacific Gas & Electric Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
DCL-10-149
Download: ML103300051 (9)

Text

Pacific Gas and Electric Company James R. Becker Diablo Canyon Power Plant Site Vice President Mail Code 104/5/601

p. O. Box 56 Avila Beach, CA 93424 805.545.3462 Internal: 691.3462 November 24, 2010 Fax: 805.545.6445 PG&E Letter DCL-1 0-149 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Docket No. 50-323, OL-DPR-82 Diablo Canyon Unit 2 Response to NRC Request for Additional Information Regarding the 180-Day Steam Generator Report for Diablo Canyon Power Plant Unit 2 Fifteenth Refueling Outage

Dear Commissioners and Staff:

Pacific Gas and Electric Company (PG&E) Letter DCL-10-050 dated May 5,2010, submitted the "180-day Steam Generator "Report for Diablo Canyon Power Plant Unit 2 Fifteenth Refueling Outage." The NRC requested additional information regarding the 180-day steam generator report by email dated September 27,2010 (ML102980282).

Enclosed are the NRC questions and PG&E's response to each question.

PG&E makes no regulatory commitments (as defined by NEI 99-04) in this letter.

This letter includes no revisions to existing regulatory commitments.

If you have any questions or require additional information, please contact Tom Baldwin at (805) 545-4720.

pns3/6984/50343949 Enclosure cc/enc: Elmo E. Collins, NRC Region IV Michael S. Peck, NRC, Senior Resident Inspector Alan B. Wang, Project Manager, Office of Nuclear Reactor Regulation Diablo Distribution

Enclosure PG&E Letter DCL-10-149 PG&E Response to NRC Request for Additional Information Regarding the 180-Day Steam Generator Report for Diablo Canyon Power Plant Unit 2 Fifteenth Refueling Outage NRC Question 1:

1. Please provide the following information pertaining to your steam generators (SGs):

Tubesheet map depicting the row and column numbers Sketch of the SG depicting the tube support naming convention The thickness of the tubesheet with and without cladding Tube support plate material and thickness U-bend support material and design Steam generator fabricator Tube manufacturer Tube pitch Method and extent of tube expansion within the tubesheet (e.g., hydraulic)

Tube support plate hole configuration (e.g., quatrefoil shaped openings)

Extent to which any tubes were stress relieved following bending Smallest U-bend radius and associated tube row PG&E Response:

Tubesheet map depicting the row and column numbers.

Figure 1 provides the Westinghouse Delta 54 SG tubesheet map depicting the row and column numbers.

Sketch of the SG depicting the tube support naming convention.

Figure 2 provides the Westinghouse Delta 54 SG sketch depicting the tube support plate naming convention.

The thickness of the tubesheet with and without cladding.

The tubesheet is 23.55 inches thick, including the 0.30-inch cladding. It is 23.25 inches thick without the cladding.

Tube support plate material and thickness.

The eight tube support plates (TSP) are stainless steel (Type 405) and are 1.125 inches thick.

1

Enclosure PG&E Letter DCL-10-149 U-bend support material and design.

In the U-bend, the tubes are supported by three sets of V shaped, rectangular stainless steel (Type 405) anti-vibration bars (AVB). The AVB assemblies stiffen the U-bend region of the tube bundle and facilitate proper tube spacing and tube alignment while mitigating tube vibration. The Diablo Canyon Power Plant replacement steam generator AVB utilize a larger width compared to the original steam generator design to reduce the potential for tube wear at AVB intersections. The lowest set of AVB assemblies supports the tubes in rows 8 through 96. The middle set of AVB assemblies support the tubes in rows 22 through 96. The upper set of AVB assemblies support the tubes in rows 43 through 96.

Steam generator fabricator.

The SG fabricator was Ensa.

Tube manufacturer.

The tube manufacturer was Sandvik.

Tube pitch.

The tubes are arranged in a triangular pattern of 96 rows (parallel to the tube lane) and 119 columns (perpendicular to the tubelane). The triangular pitch is 1.144 inches.

Method and extent of tube expansion within the tubesheet (e.g., hydraulic).

The tubes are full depth hydraulically expanded within the tubesheet. The end of each tube is tack expanded using a urethane plug expansion process.

Tube support plate hole configuration (e.g., quatrefoil shaped openings).

All tube support plates have trefoil-shaped holes, produced by broaching.

Extent to which any tubes were stress relieved following bending.

The tubes in rows 1 through 16 were full-length stress relieved following bending.

Smallest U-bend radius and associated tube row.

Row 1 has the smallest U-bend radius of 3.25 inches.

2

Enclosure PG&E Letter DCL-10-149 NRC Question 2:

On page 4 of your May 5, 2010 letter, it states that 12 tubes were reported with proximity indication signals in the U-bend region. Please identify the tubes and discuss the cause of the indications.

PG&E Response:

As discussed in PG&E's May 5, 2010 letter, 12 tubes were reported with proximity signals (PRO) in the U-bend region during both the preservice inspection (PSI) bobbin coil inspection and the Unit 2 fifteenth refueling outage (2R15) inservice inspection with bobbin and +Point. No tube wear is associated with the signals. These U-bend signals are attributed to the proximity of a given tube to another tube. Signals are reported in pairs of adjacent tubes in the same column at nearly the same axial location along the tube. This confirms that the signal pairs are related to each other in that each tube contributed to the signal in the other.

Table 1 provides a list of the tubes with PRO signals in 2R15, along with the location of the signals in the U-bend and the associated bobbin voltage. The signals occur in high radius U-bends at the flank locations of the bend region.

The logical cause of the proximity indications is a reduced tube-to-tube gap condition. A proximity signal can be generated on the bobbin coil if two tubes experience such a condition. A potential cause of a reduced tube-to-tube gap condition is manufacturing tolerances on a tube-to-tube basis, such as tolerances on U-bend profile and tube overall height. A tolerance stack-up indicates that a reduced gap may occur but tube-to-tube contact is not possible. Manufacturing tolerances on the U-bend profile are slightly larger in higher radius U-bend tubes.

Westinghouse has noted that this condition is not new to the industry. Westinghouse indicates that the tubes are not contacting each other based on the signal amplitude responses observed during 2R15 and on eddy current testing performed in support of another operating unit with the same condition.

NRC Question 3:

Please clarify what the trough region is that is referenced in Section g.3.3 of your May 5, 2010 letter.

PG&E Response:

The trough region is a peripheral secondary side groove with a 2-inch corner radius, thus a 4-inch wide trough. The groove extends to a depth of 3.75 inches below the top of tubesheet and extends around the entire tubesheet. The trough has two drain holes 3

Enclosure PG&E Letter DCL-10-149 that connect to the integrated blowdown line. The purpose of the trough is to allow the top of tubesheet to fully drain.

4

Enclosure PG&E Letter DCL-10-149 Table 1 2R15 Bobbin Proximity Indications (PRO)

Bobbin Bobbin SG Row Col Volts Indication Elevation From - To 21 94 54 0.64 PRO AV1 11.19 TO+37.92 21 96 54 1.48 PRO 8H 19.96 TO+67.59 22 93 47 0.73 PRO AV4 20.5 TO+55.12 22 95 47 0.71 PRO AV4 13.57 TO+58.38 22 93 73 0.67 PRO AV4 2.66 TO+48.21 22 95 73 0.79 PRO AV4 2.78 TO+45.07 23 94 62 1.49 PRO AV1 7.41 TO+32.05 23 96 62 1.02 PRO AV1 11.64 TO+24.74 24 89 69 0.8 PRO AV5 1.2 TO+44.51 24 91 69 0.65 PRO AV5 1.63 TO+49.08 24 93 73 0.87 PRO AV4 8 TO+54.40 24 95 73 0.52 PRO AV4 1.78 TO+51.68 5

Enclosure PG&E Letter DCL-10-149 Figure 1 DCPP Unit 1 and 2 Westinghouse Delta 54 Steam Generator Tubesheet Map Rows Columns 6

Enclosure PG&E Letter DCL-10-149 AV3 AV4 AV2 AV5 AV1 AV6 08H 08C 44.00" 07H 07C 44.00" 06H 06C 44.00" 05C 05H 44.00" 04H 04C 44.00" 03H 03C 44.00" 02H 02C 44.00" 01H 01C 20.55" TSH TSC 23.55" TEH TEC ROW 96 ROW 8 ROW 1 Westinghouse Delta 54 RSG Support thickness is 1.125" TSP Spacing values are center to center Figure 2 Sketch of DCPP Unit 1 and 2 Westinghouse Delta 54 Steam Generator 7

LAR/RAI COMMITMENT TRACKING MEMO (Remove prior to NRC submittal)

Document: PG&E Letter DCL-10-149

Subject:

Response to NRC Request for Additional Information Regarding the 180-Day Steam Generator Report for Diablo Canyon Power Plant Unit 2 Fifteenth Refueling Outage File Location S:\RS\Draft DCLs\RAI Response to 2R15 SG Report.doc FSAR Update Review Utilizing the guidance in XI3.ID2, does the FSAR Update need to be revised?

Yes No If "Yes", submit an FSAR Update Change Request in accordance with XI3.ID2 (or if this is an LAR, process in accordance with WG-9)

Statement of Commitment:

N/A Clarification: None BEFORE OR AFTER LICENSE AMENDMENT RECEIPT When will commitment be implemented?

Notification/Order # Task/Operation #

Tracking Document:

NAME ORGANIZATION CODE Assigned To:

FIRM or TARGET DUE DATE:

Commitment Code:

YES or NO IF YES, WHICH? (E.G., 2R9, 1R10, ETC.)

Outage Commitment?

YES (Specify #) or NO IF YES, LIST THE IMPLEMENTING DOCUMENTS (IF KNOWN)

New PCD Commitment?

YES (Specify #) or NO IF YES, CLARIFY HOW COMMITMENT IS TO BE REVISED Modifies Existing Commitment in PCD?

Ensure that commitment issues are addressed in the submittal cover letter per XI4.ID1.