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

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{{#Wiki_filter:Pacific Gas and Electric Company No v e m ber 24, 2010 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 James R. Becker Site Vice President Diablo Canyon Power Plant Mail Code 104/5/601
{{#Wiki_filter:Pacific Gas and Electric Company                                         James R. Becker    Diablo Canyon Power Plant Site Vice President Mail Code 104/5/601
: p. O. Box 56 Av il a Beac h , CA 93424 805.545.3462 I nterna l: 691.3462 Fax: 805.545.6445 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  
: 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
" 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).
 
==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.
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.
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.
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
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


1 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:
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):
: 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 wit hin 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  
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)
PG&E Response
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.
Tubesheet map depicting the row and column numbers.
Figure 1 provides the Westinghouse De lta 54 SG 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 t he tube support naming convention.
Sketch of the SG depicting the tube support naming convention.
Figure 2 provides the Westinghouse De lta 54 SG sketch depicting the tube support plate naming convention.
Figure 2 provides the Westinghouse Delta 54 SG sketch depicting the tube support plate naming convention.
The thickness of the t ubesheet with and without cladding.
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.
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.
Tube support plate material and thickness.
The eight tube support plates (TSP) are stainless steel (Type 405) and are 1.125 inches thick.  
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
 
2  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-vibrati on bars (AVB). The AVB assemblies stiffen the U-bend region of the tube bundle and fac ilitate proper tube spacing and tube alignment while mitigating tube vibrat ion. The Diablo Canyon Power Plant replacement steam generator AVB utilize a larger width compared to the original steam generator design to reduce t he 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  
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.
through 96.
Steam generator fabricator.
Steam generator fabricator.
The SG fabricator was Ensa.
The SG fabricator was Ensa.
Line 55: Line 52:
The tube manufacturer was Sandvik.
The tube manufacturer was Sandvik.
Tube pitch.
Tube pitch.
The tubes are arranged in a triangular patte rn of 96 rows (parallel to the tube lane) and 119 columns (perpendicular to the tubelane). The triangular pitch is 1.144 inches.
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 wit hin the tubesheet (e.g., hydraulic).
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.  
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).
Tube support plate hole configurati on (e.g., quatrefoil shaped openings).
All tube support plates have trefoil-shaped holes, produced by broaching.
All tube support plates have trefoil-shaped holes, produced by broaching.
Extent to which any tubes were stress relieved following bending.
Extent to which any tubes were stress relieved following bending.
The tubes in rows 1 through 16 were full-length 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.
Smallest U-bend radius and associated tube row.
Row 1 has the smallest U-bend radius of 3.25 inches.  
Row 1 has the smallest U-bend radius of 3.25 inches.
 
2
Enclosure PG&E Letter DCL-10-149
 
3 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 r egion. Please identify the tubes and discuss the cause of the indications.


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:
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.
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 refue ling outage (2R15) inservice inspection with bobbin and +Point. No tube wear is associated with the signals. These U-bend signals  
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.
are attributed to the proximity of a given t ube 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.  
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.
 
Table 1 provides a list of the tubes with PR O 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 indicati ons 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 reduc ed 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 indi cates that a reduced gap may occur but tube-to-tube contact is not possible. Manufac turing 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 contacti ng each other based on the signal amplitude responses observed during 2R15 and on eddy cu rrent testing performed in support of another operating unit with the same condition.  
 
NRC Question 3:
NRC Question 3:
Please clarify what the "trough region" is that is referenc ed in Section g.3.3 of your May 5, 2010 letter.  
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


PG&E Response:
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


The trough region is a peripheral secondary si de 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 Enclosure PG&E Letter DCL-10-149 4 that connect to the integrated blowdown line.
Enclosure PG&E Letter DCL-10-149 Table 1 2R15 Bobbin Proximity Indications (PRO)
The purpose of the trough is to allow the top of tubesheet to fully drain.
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


5 Table 1 2R15 Bobbin Proximity Indications (PRO)
Enclosure PG&E Letter DCL-10-149 Figure 1 DCPP Unit 1 and 2 Westinghouse Delta 54 Steam Generator Tubesheet Map Rows Columns 6
SG Row Col Bobbin Volts Bobbin 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 Enclosure PG&E Letter DCL-10-149  


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


7  Figure 2  Sketch of DCPP Unit 1 and 2 Westinghouse Delta 54 Steam Generator TEHTSH01H 02H03H04H05H06H07H08HWestinghouse Delta 54 RSG ROW 1ROW 96AV1 AV2 AV3AV4 AV5AV644.00"44.00"44.00"44.00"44.00"44.00"44.00"20.55"23.55"08C07C06C05C04C03C02C01CTSCTEC ROW 8Support thickness is 1.125"TSP Spacing values are center to center LAR/RAI COMMITMENT TRACKING MEMO (Remove prior to NRC submittal)
LAR/RAI COMMITMENT TRACKING MEMO (Remove prior to NRC submittal)
Document:
Document:         PG&E Letter DCL-10-149
PG&E Letter DCL-10-149


==Subject:==
==Subject:==
Response to NRC Request for Additional Information Regarding the 180-Day Steam Generator Report for Di ablo Canyon Power Plant Unit 2 Fifteenth Refueling Outage File Location S:\RS\Draft DCLs\RA I Response to 2R15 SG Report.doc FSAR Update Review Utilizing the guidance in XI3.ID2, does the FSAR Update need to be revised?
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 XI 3.ID2 (or if this is an LAR, process in accordance with WG-9)
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:
Statement of Commitment:
N/A Clarification
N/A Clarification: None BEFORE OR AFTER LICENSE AMENDMENT RECEIPT When will commitment be implemented?
: None   BEFORE OR AFTER LICENSE AMENDMENT RECEIPT When will commitment be implemented?
Notification/Order #         Task/Operation #
Notification/Order # Task/Operation # Tracking Document:
Tracking Document:
NAME ORGANIZATION CODE Assigned To:
NAME                         ORGANIZATION CODE Assigned To:
FIRM or TARGET DUE DATE: Commitment Code:
FIRM or TARGET               DUE DATE:
YES or NO IF YES, WHICH? (E.G., 2R9, 1R10, ETC.) Outage Commitment?
Commitment Code:
YES (Specify #) or NO IF YES, LIST THE IMPLEMENTING DOCUMENTS (IF KNOWN) New PCD Commitment?
YES or NO                     IF YES, WHICH? (E.G., 2R9, 1R10, ETC.)
YES (Specify #) or NO IF YES, CLARIFY HOW COMMITMENT IS TO BE REVISED Modifies Existing Commitment in PCD?
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.}}
Ensure that commitment issues are addressed in the submittal cover letter per XI4.ID1.}}

Revision as of 05:45, 13 November 2019

Response to NRC Request for Additional Information Regarding the 180-Day Steam Generator Report for Fifteenth Refueling Outage
ML103300051
Person / Time
Site: Diablo Canyon Pacific Gas & Electric icon.png
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)
v • d • e


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.

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