DCL-07-009, Additional Commitments Related to Inspection and Mitigation of Alloy 600/82/182 Pressurizer Butt Welds

Additional Commitments Related to Inspection and Mitigation of Alloy 600/82/182 Pressurizer Butt Welds

ML070580128
Person / Time
Site:	Diablo Canyon
Issue date:	02/20/2007
From:	Keenan J Pacific Gas & Electric Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
DCL-07-009, DCL-07-019
Download: ML070580128 (6)

Text

PacificGas and ElectricCompany' John S. Keenan 77 Beale Street, Mailcode B32 Senior Vice President San Francisco, CA 94105 Generation & Chief Nuclear Officer Mailing Address Mail Code B32, Room 3235 February 20, 2007 P0..Bx7oo P. Box 770000 San Francisco, CA 94177 415.973.4684 PG&E Letter DCL-07-019 Internal: 223.4684 Fax: 415.973.2313 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C. 20555-0001 Docket No. 50-275, OL-DPR-80 Docket No. 50-323, OL-DPR-82 Diablo Canyon Units 1 and 2 Additional Commitments Related to Inspection and Mitigation of Alloy 600/82/182 Pressurizer Butt Welds

Dear Commissioners and Staff:

In Pacific Gas and Electric (PG&E) Letter DCL-07-009, "Inspection and Mitigation of Alloy 600/82/182 Pressurizer Butt Welds," dated January 31, 2007, PG&E committed to actions planned for Diablo Canyon Power Plant (DCPP) Unit 2 related to inspecting or mitigating Alloy 600/82/182 butt welds on pressurizer spray, surge, and relief lines. As stated in PG&E Letter DCL-07-009, inspection or mitigation of pressurizer Alloy 600/82/182 butt welds, as described in MRP-1 39, has not yet been completed for DCPP Unit 2, but PG&E intends to complete all the inspection and mitigation activities on these locations during the DCPP Unit 2 Fourteenth Refueling Outage (2R14) currently scheduled to begin February 4, 2008. There are no actions required for the DCPP Unit 1 pressurizer, since it does not contain Alloy 600/82/182 butt welds.

In a phone call held with the NRC staff on February 12, 2007, the staff required that additional commitments be made in order to meet current NRC expectations to address issues associated with Alloy 600/82/182 butt welds. The additional commitments requested by the NRC are contained in this letter. PG&E previously confirmed verbally to the DCPP NRC Project Manager to make these commitments in a phone call on February 15, 2007. The additional commitments described herein only apply to DCPP Unit 2, and will be implemented from February 20, 2007, until the DCPP Unit 2 pressurizer butt welds are mitigated.

In PG&E Letter DCL-07-009, PG&E stated that it was evaluating Pressurized Water Reactor Owners Group standardized leak monitoring guidance and an NRC proposed leakage detection program, and that PG&E will inform the NRC if there are any planned changes to the leak monitoring program by March 31, 2007. Therefore, consistent with PG&E's commitment to inform the NRC of changes to the leak monitoring program, herein PG&E describes additional leak monitoring it 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-07-019 February 20, 2007 Page 2 intends to implement as a result of the phone call held with the NRC staff on February 12, 2007.

Enhanced Reactor Coolant System (RCS) Leakage Monitoring Program PG&E will implement an enhanced RCS leakage monitoring program for DCPP Unit 2 with the following elements, which supplement the existing plant programs and procedures and will be in place until the DCPP Unit 2 pressurizer alloy butt welds have been successfully mitigated:

Daily measurement of unidentified leakage, or within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> of obtaining steady state conditions.

Identification of unidentified leakage rates greater than either of the following limits when this increase is maintained for 3 days:

0 0.25 gallons per minute (gpm) greater than a baseline value. The baseline is established at the leak rate value obtained following 7 days of Mode 1 at 100 percent power operation after startup following the last bare metal visual examination of the pressurizer Alloy 600/82/182 butt weld locations.

• 0.1 gpm increase between two consecutive daily measurements.

If unidentified leakage exceeds either limit, identify the source within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> or shutdown the plant, and perform bare metal visual examinations of all pressurizer Alloy 600/82/182 butt weld locations. Following the initiation of a shutdown, the plant must be in Hot Standby in 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and in Cold Shutdown in 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br />.

If PG&E determines that the source of the unidentified leakage did not come from the pressurizer butt welds, then it is not necessary to shutdown and/or conduct bare metal examination of all Alloy 600/82/182 pressurizer butt welds.

If a quantity of leakage can be assigned to a source other than the pressurizer, and that quantity decreases the unidentified leakage below one of the thresholds (0.1 gpm step increase or 0.25 gpm above baseline), this will negate the requirement for shutdown and/or pressurizer Alloy 600/82/182 butt weld bare metal examination.

Report results of any bare metal visual inspections required to the NRC within 60 days of plant startup.

A member of the STARS (Strategic Teaming and Resource Sharing) Alliance Callaway 9 Comanche Peak

• Diablo Canyon e Palo Verde

• South Texas Project

• Wolf Creek

Document Control Desk PG&E Letter DCL-07-019 February 20, 2007 Page 3 For implementation of the 0.1 gpm increase threshold, PG&E will consider calculated leak rate values, which are negative to be zero.

The enhanced leakage monitoring program may introduce new unintended consequences which will be addressed on a case by case basis when they occur (e.g., change in leak rate due to power level changes, change in leak rate due to difference between plant process computer calculation versus manual calculation).

Acceleration of Outages for Adverse Analytical or Inspection Outcomes PG&E will accelerate the mitigation actions, currently scheduled during the 2R14 outage to begin February 4, 2008, into 2007 if the results of ongoing analytical work do not demonstrate to the NRC that the current schedule is adequate. The mitigation actions could also be accelerated if new information is obtained during upcoming inspections that challenge current assumptions.

Reportinci PG&E will report the results of DCPP Unit 2 bare metal visual inspections, MRP-139 inspections, or corrective and mitigation actions to the NRC within 60 days following restart from the plant outage in which the inspections or actions were completed.

Reinspection Frequency PG&E will reinspect the DCPP Unit 2 pressurizer butt welds within every four years until they are removed from service or mitigated!

The Enclosure contains a list of commitments associated with this letter.

PG&E will inform the NRC prior to any revision of the pressurizer butt weld inspection schedules or commitments described in this letter.

If there are any questions, please contact Stan Ketelsen at 805-545-4720.

Sincerely,

/john . 4 enan Senior Vice President- Generation and ChiefNuclear Officer 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-07-019 February 20, 2007 Page 4 kjse/4328 Enclosure cc: Edgar Bailey, DHS Terry W. Jackson Bruce S. Mallett Diablo Distribution cc/enc: Alan B. Wang A member of the STARS (Strategic Teaming and Resource Sharing) Alliance Callaway

• Comanche Peak a Diablo Canyon ° Palo Verde

• South Texas Project e Wolf Creek

Enclosure PG&E Letter DCL-07-019 COMMITMENTS Commitment 1 PG&E will implement an enhanced Reactor Coolant System leakage monitoring program for Diablo Canyon Power Plant Unit 2 with the following elements, which supplement the existing plant programs and procedures and will be in place until the DCPP Unit 2 pressurizer alloy butt welds have been successfully mitigated:

Daily measurement of unidentified leakage, or within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> of obtaining steady state conditions.

Identification of unidentified leakage rates greater than either of the following limits when this increase is maintained for 3 days:

• 0.25 gallons per minute (gpm) greater than a baseline value. The baseline is established at the leak rate value obtained following 7 days of Mode 1 at 100 percent power operation after startup following the last bare metal visual examination of the pressurizer Alloy 600/82/182 butt weld locations.

• 0.1 gpm increase between two consecutive daily measurements.

If unidentified leakage exceeds either limit, identify the source within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> or shutdown the plant, and perform bare metal visual examinations of all pressurizer Alloy 600/82/182 butt weld locations. Following the initiation of a shutdown, the plant must be in Hot Standby in 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and in Cold Shutdown in 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br />.

If PG&E determines that the source of the unidentified leakage did not come from the pressurizer butt welds, then it is not necessary to shutdown and/or conduct bare metal examination of all Alloy 600/82/182 pressurizer butt welds.

If a quantity of leakage can be assigned to a source other than the pressurizer, and that quantity decreases the unidentified leakage below one of the thresholds (0.1 gpm step increase or 0.25 gpm above baseline), this will negate the requirement for shutdown and/or pressurizer Alloy 600/82/182 butt weld bare metal examination.

Report results of any bare metal visual inspections required to the NRC within 60 days of plant startup.

For implementation of the 0.1 gpm increase threshold, PG&E will consider calculated leak rate values, which are negative to be zero.

1

Enclosure PG&E Letter DCL-07-019 Commitment 2 PG&E will accelerate the mitigation actions, currently scheduled during the DCPP Unit 2 fourteenth refueling outage to begin February 4, 2008, into 2007 if the results of ongoing analytical work do not demonstrate to the NRC that the current schedule is adequate.

The mitigation actions could also be accelerated if new information is obtained during upcoming inspections that challenge current assumptions.

Commitment 3 PG&E will report the results of DCPP Unit 2 bare metal visual inspections, MRP-139 inspections, or corrective and mitigation actions to the NRC within 60 days following restart from the plant outage in which the inspections or actions were completed.

Commitment 4 PG&E will reinspect the DCPP Unit 2 pressurizer butt welds within every four years until they are removed from service or mitigated.

Commitment 5 PG&E will inform the NRC prior to any revision of the pressurizer butt weld inspection schedules or commitments described in this letter.

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