DCL-13-024, Supplement to ASME Section XI Inservice Inspection Program Relief Request REP-1 U2, Revision 2

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Supplement to ASME Section XI Inservice Inspection Program Relief Request REP-1 U2, Revision 2
ML13067A343
Person / Time
Site: Diablo Canyon Pacific Gas & Electric icon.png
Issue date: 03/07/2013
From: Allen B
Pacific Gas & Electric Co
To:
Office of Nuclear Reactor Regulation, Document Control Desk
References
DCL-13-024
Download: ML13067A343 (4)
v • d • e


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 March 7, 2013 Internal: 691.4888 Fax: 805.545 . 6445 PG&E Letter DCL-13-024 U.S. Nuclear Regulatory Commission 10 CFR 50.55a ATTN: Document Control Desk Washington, DC 20555-0001 Docket No. 50-323, OL-DPR-82 Diablo Canyon Unit 2 Supplement to ASME Section XI Inservice Inspection Program Relief Request REP-1 U2, Revision 2

References:

1. PG&E Letter DCL-07-038, "ASME Section XI Inservice Inspection Program Relief Request REP-1 U2," dated March 28, 2007.
2. PG&E Letter DCL-07-099, "ASME Section XI Inservice Inspection Program Relief Request REP-1 U2, Revision 1, and Response to Request for Additional Information," dated October 22, 2007.
3. PG&E Letter DCL-07-105, "ASME Section Xllnservice Inspection Program Relief Request REP-1 U2, Revision 1; Response to Request for Additional Information," dated November 29, 2007.
4. NRC Letter, "Diablo Canyon Power Plant, Unit No.2 - Approval of Relief Request REP-1 U2, Revision 1, for the Application of Weld Overlay on Dissimilar Metal Welds of Pressurizer Nozzles (TAC No. MD4974 )," dated February 6, 2008.
5. PG&E Letter DCL-13-021, "ASME Section XI Inservice Inspection Program Relief Request REP-1 U2, Revision 2,"

dated March 5,2013.

Dear Commissioners and Staff:

On March 5, 2013 Pacific Gas and Electric Company (PG&E) submitted

. Reference 5, pursuant to 10 CFR 50.55a(a)(3)(i), requesting NRC approval for ASME Section XI Inservice Inspection Program Relief Request REP-1 U2, Revision 2. PG&E is submitting this supplement to clarify that all of Relief Request REP-1 U2, Revision 2 is pursuant to 10 CFR 50.55a(a)(3)(i) except for Sections 3.a.(3)(a)(i) and ii) of Attachment 1 to Enclosure 1 of Reference 5.

These two sections are requested for NRC authorization pursuant to 10 CFR 50.55a(a)(3)(ii).

A member of the STARS (Strategic Teaming and Resource Sharing) Alliance Callaway

  • Comanche Peak
  • Diablo Canyon
  • Palo Verde
  • Wolf Creek

Document Control Desk PG&E Letter DCL-13-024 March 7,2013 Page 2 The Enclosure to this letter contains a revised Section 5.13, "Potential Hardship,"

of Enclosure 1 to Reference 5 as the basis for hardship without a compensating increase in the level of quality and safety for Sections 3.a.(3)(a)(i) and ii) of of Enclosure 1 to Reference 5.

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.

Sincerely, J5 &A-a-7 Barry S. Allen Site Vice President pns3/6984 SAPN 50540188 Enclosure cc: Diablo Distribution cc/enc: Gonzalo L. Perez, Branch Chief, California Department of Public Health Elmo E. Collins, 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
  • Wolf Creek

Enclosure PG&E Letter DCL-13-024 Revised Section 5.13, "Potential Hardship," of Enclosure 1 to PG&E Letter DCL-13-021, "ASME Section Xllnservice Inspection Program Relief Request REP-1 U2, Revision 2," dated March 5, 2013 5.13 Potential Hardship To restore the weld overlays to compliance with the 3-inch linear dimension requirement specified in the relief request, the flaws in the overlays will have to be excavated and repaired using the same automated welding process with which they were originally installed. The repairs of the overlays present a hardship for the following reasons:

1. Repairs to the weld overlay would be required on two safety relief valve nozzles and the pressurizer spray nozzle. These pressurizer nozzles are located at the top of the pressurizer, which is approximately 25 feet from the containment floor with intervening hazards. Repair of the overlays will expose personnel to potential fall hazards. Exacerbating the fall hazard is the tight and awkward environment in which the work is required to be performed, requiring workers to maneuver around pipes and openings in grating.
2. Completion of the repair would incur increased dose. Although the average effective dose rate is not excessive in the area (approximately 4.5 mR per hour), the amount of work and number of people required to prepare, perform, monitor, inspect and demobilize from the repair is such that the total dose accumulated is high. Based on the current schedule and personnel estimates, the total dose required to perform the repair work is at least 2.6 Rem. This would result in this single activity being approximately 10 percent or more of the total dose expected for this outage.
3. Excavation and repair of the overlays has the potential to degrade the overlay and beneficial compressive stress on the inner diameter of the nozzles.
a. The flaws would be excavated, creating a cavity that would be repair welded. However, the weld cavity will reduce welding accessibility as compared to the original welding operation. The decreased accessibility will make performance of the welds more difficult and create the possibility of introduction of additional flaws that would then require subsequent excavation and repair, increasing the total time that personnel are exposed to fall hazards and the total dose for the work.
b. The potential for incomplete inter-bead and side wall fusion is much greater when welding in narrow cavities as compared to the original 1

Enclosure PG&E Letter DCL-13-024 structural weld overlay installation. These flaws are more likely to have a planar orientation due to incomplete fusion to the side wall of the repair cavity. Even though these flaws may be acceptable to the NDE requirements, they may be more detrimental to the integrity of the weld overlay than the laminar flaws that were removed by the repair.

c. Weld thermal cycles on a multilayer Alloy 52M excavation increases the risk of ductility dip cracking and opening of grain boundaries. Multiple repairs also increase the risk of forming deleterious phases such as Laves phase, which can promote liquation cracking.
d. Grinding and welding will potentially alter the stress profile of the overlay. Although the design of the repair would be planned to minimize the impact on the overall effectiveness of the overlay, the potential exists to decrease the beneficial compressive stress that the weld overlay imparts to the inner surface of the nozzle. The compressive stress decreases the probability of primary water stress corrosion cracking in the susceptible material by reducing the stress responsible for crack initiation and propagation.
4. Grinding will be required to excavate the flaws prior to weld repair.

Because the flaws cannot be readily seen, complete flaw removal cannot be assured until the weld repair is completed and a post-repair ultrasonic test is performed. If flaws are identified that do not meet the acceptance criteria of the relief request, additional grinding and repair would be required, further increasing the potential to introduce localized stress and increase personnel exposure to fall hazards and radiation.

5. The installation of the original weld overlays required rework of pipe hangers and realignment of piping. Although the repair work is not as extensive as the original overlay work, it does have the potential to require rework of some pipe hangars and cutting and re-welding to realign the discharge piping for the two safety relief valves that would require repairs.

This would further increase personnel exposure to fall hazards and radiation.

Based on the structural analysis and fracture mechanics flaw growth analyses that have been performed that demonstrates that the existing structural integrity of the weld overlay is acceptable with significant margin, repair of the identified flaws on safety relief valve nozzles A, B and the pressurizer spray line nozzle does not provide a compensating increase in safety to offset the hardships discussed above.

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