DCL-11-101, (DCPP) Unit 1, ASME Section XI Inservice Inspection Program Request for Alternative NDE-RCS-SE-LP1 Cl to Allow Use of Alternate ASME Code Case N-770-1 Baseline Exam
| ML112690216 | |
| Person / Time | |
|---|---|
| Site: | Diablo Canyon  |
| Issue date: | 09/22/2011 |
| From: | Becker J Pacific Gas & Electric Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| DCL-11-101 | |
| Download: ML112690216 (7) | |
Text
Pacific Gas and Electric Company September 22, 201 1 PG&E Letter DCL-11 -101 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Docket No. 50-275, OL-DPR-80 Diablo Canyon Power Plant (DCPP) Unit 1 James R. Becker Site Vice President Diablo Canyon Power Plant Mail Code 104/ 5/ 601
- p. O. Box 56 Avila Beach, CA 93424 805.545.3462 Internal: 691.3462 Fax: 805.545.6445 10 CFR 50.55a ASME Section XI Inservice Inspection Program Request for Alternative NDE-RCS-SE-LP1 CL to Allow Use of Alternate ASME Code Case N-770-1 Baseline Exam
Dear Commissioners and Staff:
Pursuant to 10 CFR 50.55a(a)(3)(ii), Pacific Gas and Electric Company (PG&E) hereby requests NRC approval of Inservice Inspection (lSI) Proposed Alternative NDE-RCS-SE-LP1 CL for the DCPP Unit 1 third lSI Interval. The details of the proposed alternative are enclosed.
This request is associated with the use of an alternative to the requirements of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code, Code Case N-770-1 as conditioned in the Final Rule 10 CFR 50.55a(g)(6)(ii)(F)(3) dated June 21, 2011.
To support planning for the upcoming Unit 1 seventeenth refueling outage scheduled for April 2012, PG&E requests approval of NDE-RCS-SE-LP1 CL by February 1,2012.
PG&E makes no regulatory commitments (as defined by NEI 99-04) in this letter.
If you have any questions or require additional information, please contact Tom Baldwin at (805) 545-4720.
Sincerely, mjrm/4557 Enclosure A member of the STA~S (Strategic Teaming and Resource Sharing) Alliance Callaway
- Comanche Peak
- Diablo Canyon
- Palo Verde
- South Texas Project
- Wolf Creek
.1 Document Control Desk
~&~ September 22,2011 Page 2 Diablo Distribution PG&E Letter DCL-11-1 01 cc:
cc/enc:
Elmo E. Collins, Regional Administrator, NRC Region IV Michael S. Peck, NRC Senior Resident Inspector James T. Polickoski, NRR Project Manager Alan B. Wang, 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-11-1 01 10 CFR 50.55a Request NDE-RCS-SE.. lP1Cl Proposed Alternative in Accordance with 10 CFR 50.55a(a)(3)(ii)
--Hardship or Unusual Difficulty Without Compensating Increase in Level of Quality or Safety--
- 1.
ASME Code Component Affected Diablo Canyon Power Plant (DCPP) Unit 1, Loop 1 reactor vessel (RV) cold leg nozzle-to-safe-end weld. The affected component is identified below. See Figure 1 of this enclosure for a sketch of the safe-end configuration and materials.
Code Cat.!
Description Weld Number Line Inside Item No.
Diameter Item B1 Loop 1 RV cold leg nozzle-WIB-RC-1-18(SE) 27.5" (R-A, R1.20) to-safe-end weld 1 ASME Code Case N-770-1 Inspection Item; previously Risk Informed Category R-A, Item R1.20. DCPP Unit 1 cold leg operating temperature is 544.5° F.
- 2.
Applicable Code Edition and Addenda
The Diablo Canyon Third Inservice Inspection Interval Program Plan is based on the American Society of Mechanical Engineering (ASME) Boiler and Pressure Vessel Code,Section XI, 2001 Edition with 2003 Addenda.
Pressure retaining dissimilar metal vessel nozzle butt welds containing Alloy 182 are subject to the requirements of ASME Code Case N-770-1, as conditioned in the Final Rule 10 CFR 50.55a(g)(6)(ii)(F)(3) which became effective June 21,2011. Appendix VIII ultrasonic piping examinations are conducted in accordance with Section XI, 2001 Edition without Addenda as implemented by the Performance Demonstration Initiative (POI).
- 3.
Applicable Code Requirement
ASME Code Case N-770-1, Inspection Item "B", "Unmitigated butt weld at Cold Leg operating temperature ;;:::525° F and < 580° F" specifies visual and volumetric examinations. Baseline and subsequent volumetric examinations are to be conducted in accordance with ASME Section XI, Appendix VIII, Supplement 10.
1
- 4.
Reason for Request
Enclosure PG&E Letter DCL-11-101 An Alternative is requested to the "Code required examination volume of essentially 100 percent" of Code Case N-770-1 as conditioned in 10 CFR 50.55a(g)(6)(ii)(F)(3) for volumetric examination of the DCPP Loop 1 RV cold leg nozzle-to-safe-end weld. The proposed alternative is necessary since the surface configuration of the subject weld does not allow full coverage of the specified examination volume in the circumferential scan direction. Approval of this alternative will allow the most recent volumetric examination to be credited as a "baseline" per the regulation.
Details DCPP performed volumetric examinations of Alloy 182 hot and cold leg safe-end welds in the Unit 1 sixteenth refueling outage (1 R16) to satisfy the requirements of Materials Reliability Program (MRP)-139 R1, "Materials Reliability Program:
Primary System Piping Butt Weld Inspection and Evaluation Guideline." Exam personnel, procedures, and equipment were qualified to the POI implementation of ASME Section XI, Appendix VIII, Supplement 10 requirements.
The cold leg nozzle-to-safe-end welds were examined manually from the outside surface using ultrasonic phased-array technology. The DCPP examination procedure used for the cold leg safe-end welds implements the Electric Power Research Institute (EPRI) procedure, EPRI-DMW-PA-1 Revision 1, "Procedure for Manual Phased Array Ultrasonic Examination of Dissimilar Metal Welds".
The examination of the Loop 1 RV cold leg nozzle-to-safe-end weld did not achieve the "essentially 100 percent" coverage of the Code required examination volume due to the unique outside surface contour of the reactor nozzle forging.
The ultrasonic transducer used for circumferential scans (for detection of axially oriented flaws) was not able to maintain contact on the nozzle side of the weld for the entire distance necessary to cover the examination volume.
Circumferential scan coverage of the Code examination volume is calculated to be approximately 61 percent.
Conversely, scans of the subject weld in the axial direction (for detection of circumferentially oriented flaws) attained 100 percent coverage of the Code required examination volume. When combined, the two required scan orientations achieved an average of approximately 80 percent coverage of the Code examination volume. Although the 1 R16 examination volume coverage for the subject weld did satisfy the requirements of MRP-139 R1, it does not meet the coverage requirements of Code Case N-770-1 as conditioned in the Final Rule 10 CFR 50.55a(g)(6)(ii)(F)(3), effective June 21, 2001, for "baseline" examinations. A sketch showing the component configuration, materials, examination area, and actual coverage is included as Figure 1 of this enclosure.
2
Enclosure PG&E Letter OCL-11-1 01 The "essentially 100 percent" coverage of the Code required exam volume was attained for the remaining three cold leg nozzle-to-safe-end welds as well as the four hot leg safe-end welds in each of the axial and circumferential scan directions. No inside surface connected flaws were detected in any of the 1 R 16 reactor coolant system (RCS) examinations.
In order to reach "essentially 100 percent" coverage of the specified examination volume on the Loop 1 RV cold leg nozzle-to-safe-end weld, removal of the reactor lower internals followed by examination from the inside surface would be required. The additional personnel exposure to the plant staff due to the combined removal/exam/reinstallation evolution is estimated to be 750 mR. In addition to as low as reasonably achievable considerations, major evolutions involving heavy loads such as lower internals removal result in incremental increases to personnel safety risk and also for damage risk to plant components.
Reconfiguring the outside surface of the safe-end weld to the extent required to create a contour where contact can be maintained on the nozzle forging would involve extensive machining or hand grinding. In addition to the personnel exposure involved, the end result would be a significantly reduced wall thickness with a corresponding reduction in margin or possible minimum wall thickness violation.
- 5.
Proposed Alternative and Basis for Use PG&E proposes that the 1 R16 combined axial and circumferential exam volume coverage of approximately 80 percent provides reasonable assurance of the structural integrity of the Unit 1, Loop 1, cold leg nozzle-to-safe-end weld, and that examination may be credited as a baseline per the requirements of ASME Code Case N-770-1 as conditioned in the Final Rule 10 CFR 50.55a(g)(6)(ii)(F)(3) which became effective June 21, 2011. This proposal is based on the following:
The entire wetted surface of the root area on the Loop 1 RV cold leg nozzle-to-safe-end weld was subjected to ultrasonic phased array examination qualified in accordance with the POI implementation of ASME XI, Appendix VIII, Supplement 10 requirements (see Figure 1).
Any primary water stress corrosion cracking (PWSCC) would be expected to initiate in this area. Since this region was fully interrogated, there is reasonable assurance that axial flaws that could challenge the structural integrity of the component do not exist; industry experience indicates that it is unlikely that similar type flaws would initiate and or propagate in the uninspected exam volume which is located in the reactor nozzle low alloy steel forging and cladding.
3
Enclosure PG&E Letter OCL-11-1 01 No inside surface connected flaws were detected in any of the 1 R16 RCS hot or cold leg nozzle-to-safe-end weld examinations. Hot leg locations were inspected with POI qualified Appendix VIII ultrasonic procedures and supplemented by eddy current surface examination. These higher temperature locations are considered to be more likely to experience cracking first based on known effects of temperature on PWSCC initiation.
The hot leg examination results add confidence to the conclusion that the subject cold leg location is not structurally challenged by PWSCC.
All OCPP Unit 1 RCS safe-end welds were previously examined from the inside surface with POI qualified Appendix VIII ultrasonic procedures and personnel during the Unit 1 thirteenth refueling outage (1 R13) 10-year reactor vessel examination. The 1 R13 safe-end ultrasonic examinations were supplemented by surface profilometry and eddy current testing.
Greater than 90 percent coverage of the required exam areas was achieved for all RCS nozzle-to-safe-end welds (including the subject weld) at that time; no inside surface connected flaws were detected.
OCPP has employed RCS zinc injection since June 1998. Evidence continues to mount that zinc injection is an effective strategy for mitigation of PWSCC.
The proposed alternative baseline exam provides reasonable assurance that the structural integrity of the OCPP Unit 1, Loop 1 reactor coolant nozzle-to-safe-end weld remains intact and provides an acceptable level of quality and safety in accordance with 10 CFR 50.55a(a)(3)(ii).
- 6.
Duration of Proposed Alternative The duration of the proposed alternative is through the remainder of the OCPP Unit 1 third lSI Interval. The Unit 1 third inspection interval initiated on January 1, 2006 and is scheduled to end on May 7, 2015.
- 7.
Precedent The need for approval of alternative ASME Code Case N-770-1 baseline examinations is addressed in 10 CFR 50.55a(g)(6)(ii)(F)(3). Due to the recent effective date of regulation, no precedent exists.
4
Figure 1 Enclosure PG&E Letter DCL-11-1 01 DCPP Unit 1 Loop-1 CL Circumferential Coverage Sketch Weld # WIB-RC-1-18SE Transducer position at extent of full contact ~
Concave SUrface~j Limits Circ Scans CS Nozzle Forging (SA-508)
SSClad --
Dim~r A
B I
1III1111 r F.
B
/-.J
- -I WIB-RC-1-18(SE)
(lnconeI182, No Butter)
SS Safe-End (SA-182, Type 316)
A-B-C-O = 1.8 sq'/in.
(Code Exam Area)
B-C-E-F = 1.1 sq'/in.
(Actual Circ Scan Coverage area) 5 Loop 1 Circumferential Coverage:
1.1 /1.8 =.611 CWscan = 61.1%
CCWscan = 61.1%