DCL-13-038, ASME Section XI Inservice Inspection Program Relief Request NDE-RCS-SE-1R18 to Allow Use of Alternative Depth Sizing Criteria

ASME Section XI Inservice Inspection Program Relief Request NDE-RCS-SE-1R18 to Allow Use of Alternative Depth Sizing Criteria

ML13102A048
Person / Time
Site:	Diablo Canyon
Issue date:	04/11/2013
From:	Allen B Pacific Gas & Electric Co
To:	Office of Nuclear Reactor Regulation, Document Control Desk
References
DCL-13-038
Download: ML13102A048 (9)

Text

Pacific Gas and Electric Company Barry S. Allen Diablo Canyon Power Plant Site Vice President Mail Code 104/6 P. O. Box 56 Avila Beach, CA 93424 805.545.4888 April 11 ,2013 Internal: 691 .4888 Fax: 805.545.6445 PG&E Letter DCL-13-038 10 CFR 50.55a U.S. Nuclear Regulatory Commission ATTN: Docu ment Control Desk Washington, DC 20555-0001 Docket No. 50-275, OL-DPR-80 Diablo Canyon Power Plant (DCPP) Unit 1 ASME Section XI Inservice Inspection Program Relief Request NDE-RCS-SE-1 R18 to Allow Use of Alternative Depth Sizing Criteria

Dear Commissioners and Staff:

Pursuant to 10 CFR 50.55a(g)(5)(iii), Pacific Gas and Electric Company (PG&E) hereby requests NRC approval of Inservice Inspection (lSI) Relief Request (RR)

NDE-RCS-SE-1 R18 for the Diablo Canyon Power Plant Unit 1 third lSI interval. The details of the request are enclosed.

This request is associated with the use of alternatives to the requirements of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code,Section XI, Appendix VIII, Supplements 2 and 10 as modified by Code Case N-695, "Qualification Requirements for Dissimilar Metal Piping Welds,"

and Code Case N-696, "Qualification Requirements for Appendix VIII Piping Examinations Conducted From the Inside Surface."

To support the examinations to be performed in the upcoming Unit 1 eighteenth refueling outage scheduled for February 2014, PG&E requests approval of this RR by January 15, 2014.

This communication contains new commitments to be implemented following NRC approval of this RR. The commitments are contained in Attachment 1 of the Enclosure.

If you have any questions regarding the information enclosed, or other lSI program activities, please contact Mr. Tom Baldwin at (805) 545-4720.

Sincerely, A member of the STARS (StrategiC Teaming and Resource Sharing) Alliance Callaway

• Comanche Peak

• Diablo Canyon

• Palo Verde

• South Texas Project

• Wolf Creek

Document Control Desk PG&E Letter DCL-13-038 April 11 ,2013 Page 2 rnttJ4231/SAPN 50033145-62 Enclosure cc: Diablo Distribution celene!: Arthur T. Howell, III, NRC Region IV Thomas R. Hipschman, NRC Senior Resident Inspector James T. Polickoski, NRR Project Manager State of California, Pressure Vessel Unit A member of the STARS (Strategic Teaming and Resource Sharing) Alliance Callaway

• Comanche Peak

• Diablo Canyon

• Palo Verde

• South Texas Project

• Wolf Creek

Enclosure PG&E Letter DCL-13-038 10 CFR SO.SSa Relief Request NDE ..RCS ..SE ..1R18 Relief Request in Accordance with 10 CFR SO.SSa(g)(S)(iii)

--Inservice Inspection Impracticality--

1. ASME Code Components Affected The American Society of Mechanical Engineers (ASME)Section XI Class 1 Diablo Canyon Power Plant (DCPP) Unit 1 Reactor vessel nozzle to safe-end and safe-end to piping welds are listed below. See Figure 1 for safe-end general configuration and materials.

Code Cat.! Description Weld Number

• Line Size/

Item No.

• Nominal Wall N-770-1, A-2 Loop 1 outlet nozzle to safe-end WIB-RC-1-1 (SE) 29 in.!2.5 in.

R-A, R1.20 Loop 1 outlet safe-end to pipe WIB-RC-1-1 29 in'!2.5 in.

R-A, R1.20 Loop 1 inlet elbow to safe-end WIB-RC-1-18 27.5 in/2.38 in.

N-770-1, B Loop 1 inlet safe-end to nozzle WIB-RC-1-18(SE) 27.5 in/2.38 in.

N-770-1, A-2 29 in.!2.5 in.

Loop 2 outlet nozzle to safe-end WIB-RC-2-1 (SE)

R-A, R1.20 29 in'!2.5 in.

Loop 2 outlet safe-end to pipe WIB-RC-2-1 R-A, R1.20 27.5 in'!2.38 in.

Loop 2 inlet elbow to safe-end WIB-RC-2-20 N-770-1, B 27.5 in'!2.38 in.

Loop 2 inlet safe-end to nozzle WIB-RC-2-20(SE)

N-770-1, A-2 29 in'!2.5 in.

Loop 3 outlet nozzle to safe-end WIB-RC-3-1 (SE)

R-A, R1.20 29 in.!2.5 in.

Loop 3 outlet safe-end to pipe WIB-RC-3-1 R-A, R1.20 27.5 in'!2.38 in.

Loop 3 inlet elbow to safe-end WIB-RC-3-18 N-770-1, B 27.5 in'!2.38 in.

Loop 3 inlet safe-end to nozzle WIB-RC-3-18(SE)

N-770-1 , A-2 29 in'!2.5 in.

Loop 4 outlet nozzle to safe-end WIB-RC-4-1 (SE)

R-A, R1.20 29 in.!2.5 in.

Loop 4 outlet safe-end to pipe WIB-RC-4-1 R-A, R1.20 27.5 in'!2.38 in.

Loop 4 inlet elbow to safe-end WIB-RC-4-18 N-770-1, B 27.5 in'!2.38 in.

Loop 4 inlet safe-end to nozzle WIB-RC-4.;18(SE)

• Safe-end welds with SE suffix are dissimilar metal welds fabricated with Alloy 182 weld material and are examined in accordance with ASME Code Case N-770-1.

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Enclosure PG&E Letter DCL-13-038

2. Applicable Code Edition and Addenda

The DCPP third Inservice Inspection Interval Program Plan (lSIPP) is based on the ASME Boiler and Pressure Vessel Code,Section XI, 2001 Edition with Addenda through 2003. Appendix VIII ultrasonic piping examinations are performed in accordance with the Section XI, 2001 Edition without Addenda.

The ISIPP is augmented with the requirements of ASME Code Case N-770-1 as modified by 10 CFR 50.55a for the examination of dissimilar metal vessel nozzle butt welds containing Alloy 82/182 material. These requirements apply to the dissimilar metal welds connecting the reactor nozzles to the reactor coolant system (RCS) piping.

The DCPP lSI PP references Code Cases N-695 and N-696 which are unconditionally approved for use in NRC Regulatory Guide 1.147, Revision 16.

The DCPP Unit 1 third inspection interval commenced on January 1, 2006, and is nominally scheduled to end on May 6, 2015.

3. Applicable Code Requirement

ASME Code Case N-770-1 stipulates ultrasonic examination of dissimilar metal welds fabricated from Alloy 82/182 material. These requirements apply to the DCPP reactor nozzle to safe-end welds.

DCPP Risk Informed ISIPP examination Category R-A, Item R.120 (formerly Code Category B-F, B5.10 in the 2001 Edition through 2003 Addenda) specifies volumetric examination for the associated RCS safe-end to piping welds that are fabricated with 308 stainless steel weld material.

All of the specified ultrasonic examinations are to be conducted per Appendix VIII Supplements 2 (wrought austenitic welds) and 10 (dissimilar metal welds) with the exception of the cast side of the cold leg elbow to safe-end welds. The cast elbow sides of these welds are to be examined per Appendix III as modified by Supplement 1.

ASME Code Cases N-695 and N-696 provide alternatives to Appendix VIII Supplements 10 and 2 and include requirements for depth sizing accuracy; Code Case N-695 3.3( c) states, " ... are qualified for depth sizing when the RMS error of the flaw depth measurements, as compared to the true flaw depths, do not exceed 0.125 in. (3 mm)," while Code Case N-696 3.3(d) states, " ... qualified for depth sizing when the flaw depths estimated by ultrasonics, as compared with the true depths, do not exceed 0.125 in. (3 mm) RMS, when they are combined with a successful Supplement 10 qualification."

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Enclosure PG&E Letter OCL-13-038

4. Impracticality of Compliance Relief is requested from the 0.125 in. root mean square error (RMSE) depth sizing accuracy requirement of Code Cases N-695 and N-696.

To date, although examination vendors have qualified for detection and length sizing in accordance with the Appendix VIII requirements for examinations from the inside diameter (10), the vendors have not met the established RMSE of 0.125 in. for depth sizing despite numerous attempts.

Consequently, relief from the Code Case specified 0.125 in. RMSE depth sizing accuracy requirement is necessary to support evaluation of findings from examinations when conducted from the inside surface.

Additionally, relief is requested from implementing the requirements of ASME Appendix III as modified by Supplement 1 for the examination of the cast stainless steel side of the cold leg elbow to safe-end welds. Specific examination requirements for cast stainless steel materials are not yet addressed in Section XI. Examinations using the Appendix III, Supplement 1 process rather than the Appendix VIII Supplement 2 requirements used on the wrought side of the weld would result in additional burden without benefit. The Appendix III examinations would require separate procedures, calibration blocks, calibrations and possibly completely separate examinations.

5. Proposed Alternative and Basis for Use PG&E proposes to use a vendor qualified for 10 detection and length sizing per Appendix VIII as applicable to the welds included in this request. Indications requiring depth sizing will be treated as detailed in the following paragraphs.

Since PG&E is in the vendor selection process at the time of this submittal, references to vendor depth sizing RMSE values are generic.

The Appendix VIII examination process will also be used to examine the cast stainless steel side of the cold leg elbow to safe-end welds in lieu of Appendix III and Supplement 1 requirements. All 10 examinations will be augmented with inside surface profilometry and eddy current examination.

If a reportable flaw is detected and determined to be 10 surface connected during examination of the welds that are included in Relief Request NOE-RCS-SE-1 R18, PG&E will provide a flaw evaluation including the measured flaw size as determined by ultrasonic testing (UT) for review by NRC. Eddy current testing will be used to determine if flaws are surface connected.

Additional data including details of the surrounding 10 surface contour in the region of the flaw and percentage of the exam area where UT probe lift-off is evident, if any, will be included.

3

Enclosure PG&E Letter DCL-13-038 In the event that any flaw(s) requiring depth sizing is detected during examination of the welds that are included in Relief Request NDE-RCS-SE-1 R18, the following criteria shall be implemented:

• ID connected flaws detected and measured as less than 50 percent through-wall in depth shall be adjusted by adding a correction factor to the flaw depth such that the adjusted flaw depth is equal to the measured flaw depth plus (contractor RMSE minus 0.125 in.), prior to comparison to the applicable acceptance criteria;

• If ID connected flaw(s) are detected and measured as 50 percent through-wall depth or greater and to remain in service without mitigation or repair, PG&E shall submit flaw evaluation(s) for review and approval by NRC prior to reactor startup. The flaw evaluation shall include:

o Information concerning the mechanism that caused the flaw o Information concerning the inside surface roughness/profile of the region surrounding the flaw o Information concerning areas where UT probe lift-off is observed All welds included in this request have been previously examined from the ID with an Appendix VIII qualified detection process and length sizing in the thirteenth refueling outage. The ultrasonic examinations were supplemented by surface profilometry and eddy current testing. Greater than 90 percent coverage of the required exam areas was achieved in all cases. This inspection history confirms that the inside surface profiles of the welds included in this request are suitable for ultrasonic examination from the ID in accordance with the referenced requirements as modified by the proposed alternative sizing requirements.

In the event the proposed alternate examination process grossly mischaracterizes a significant planar flaw, the potential resulting failure of one of the RCS loop outlet/inlet welds could result in a loss of coolant accident (LOCA).

Depending on the size of the postulated break, the specific consequences will vary. At the smallest end of the break size spectrum, the charging system would be capable of maintaining RCS pressure through normal makeup. Larger break sizes would result in depressurization of the RCS, reactor trip and a safety injection. The worst case consequence would occur if one of the nozzle to pipe welds were to suffer 360 degree circumferential cracking. In this case, the break size is bounded by the line ID which is less than the break size used in the large break LOCA design basis analysis.

NRC review of vendor performance demonstration initiative qualification test results concluded that for flaw depths less than 50 percent wall thickness, reasonable assurance that a flaw will be appropriately depth sized may be 4

Enclosure PG&E Letter DCL-13-038 obtained by adding a correction factor to the flaw depth such that the adjusted flaw depth is equal to the measured flaw depth+(contractor RMSE-0.125 in.).

Therefore, the proposed alternative for correcting measured flaw depths for flaws less than 50 percent wall thickness and performing and submitting a flaw specific analysis for flaws equal to or greater than 50 percent wall thickness will have little effect on the likelihood of gross flaw mischaracterization and any potential for resulting component failure.

For the cast stainless steel side of cold leg elbow to safe-end welds, the proposed Appendix VIII 10 exam supplemented with surface profilometry and eddy current is better suited for detection of 10 connected flaws than the Code specified Appendix III, Supplement 1 process.

The DCPP Unit 1 reactor coolant nozzle to safe-end and safe-end to piping welds will be examined from the 10 using personnel, procedures and equipment qualified by demonstration in all aspects except depth sizing. The proposed method of addressing depth sizing RMSE values will compensate for the potential through-wall sizing variation and provides reasonable assurance of structural integrity in accordance with 10 CFR 50.55a(g)(5)(iii).

6. Duration of Proposed Alternative The duration of the proposed alternative is for the remainder of the DCPP Unit 1 third lSI interval, nominally scheduled to end on May 6, 2015.

7. Precedent The proposed alternative method of addressing the difference between the demonstrated and required RMSE values was approved for McGuire Nuclear Station Unit 2 by NRC letter dated September 24, 2012 (ADAMS Accession No. ML12258A363).

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Enclosure PG&E Letter DCL-13-038 Weld (Inconel182)

L Nozzle-to-Safe-End Safe-End-to-Piping Weld (308 SS)

__ l Cold Leg Elbow (A-3S1 CF8M)

/

Hot Leg SS Pipe (A-376 Type 316)

SS Clad DCPP Unit 1 Sketch of Hot Leg and Cold Leg Safe-End General Configuration Figure 1 6

Enclosure Attachment 1 PG&E Letter OCL-13-038 List of Regulatory Commitments Commitment 1 If a reportable flaw is detected and determined to be 10 surface connected during examination of the welds that are included in Relief Request NOE-RCS-SE-1 R18, PG&E will provide a flaw evaluation including the measured flaw size as determined by UT for review by NRC. Eddy current testing will be used to determine if flaws are surface connected. Additional data including details of the surrounding 10 surface contour in the region of the flaw and percentage of the exam area where UT probe lift-off is evident, if any, will be included.

Commitment 2 In the event that any flaw(s) requiring depth sizing is detected during examination of the welds that are included in Relief Request NOE-RCS-SE-1 R18, the following criteria shall be implemented:

• 10 connected flaws detected and measured as less than 50 percent through-wall in depth shall be adjusted by adding a correction factor to the flaw depth such that the adjusted flaw depth is equal to the measured flaw depth plus (contractor RMSE minus 0.125 in.), prior to comparison to the applicable acceptance criteria;

• If 10 connected flaw(s) are detected and measured as 50 percent through-wall depth or greater and to remain in service without mitigation or repair, PG&E shall submit flaw evaluation(s) for review and approval by NRC prior to reactor startup.

The flaw evaluation shall include:

o Information concerning the mechanism that caused the flaw o Information concerning the inside surface roughness/profile of the region surrounding the flaw o Information concerning areas where UT probe lift-off is observed 1