DCL-20-069, Response to NRC Request for Additional Information Regarding License Amendment Request 20-01, Exigent Request for Revision to Technical Specification 3.7.5, 'Auxiliary Feedwater System'

Response to NRC Request for Additional Information Regarding License Amendment Request 20-01, Exigent Request for Revision to Technical Specification 3.7.5, 'Auxiliary Feedwater System'

ML20231A838
Person / Time
Site:	Diablo Canyon
Issue date:	08/18/2020
From:	Gerfen P Pacific Gas & Electric Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation, NRC/OCM
References
DCL-20-069
Download: ML20231A838 (5)

Text

m PacHic Gas and Electric Company*

Paula Gerfen Site Vice President Diablo Canyon Power Plant Mail code 104/6/605 P.O. Box 56 Avila Beach, CA 93424 805.545.4596 Internal: 691.4596 Fax: 805.545.4234 August 18, 2020 PG&E Letter DCL-20-069 U.S. Nuclear Regulatory Commission 10 CFR 50.91 ATTN: Document Control Desk Washington, DC 20555-0001 Docket No. 50-275, OL-DPR-80 Docket No. 50-323, OL-DPR-82 Diablo Canyon Units 1 and 2 Response to NRC Request for Additional Information Regarding License Amendment Request 20-01, Exigent Request for Revision to Technical Specification 3.7.5, Auxiliary Feedwater System

References:

1. PG&E Letter DCL-20-066, License Amendment Request 20-01, Exigent Request for Revision to Technical Specification 3.7.5, Auxiliary Feedwater System, dated August 12, 2020, ADAMS Accession No. ML20225A303

2. PG&E Letter DCL-20-068, Response to NRC Request for Additional Information Regarding License Amendment Request 20-01, Exigent Request for Revision to Technical Specification 3.7.5, Auxiliary Feedwater System, dated August 16, 2020, ADAMS Accession No. ML20229A016

3. E-mail from NRC Senior Project Manager, Samson Lee, Diablo Canyon additional request for additional information: Exigent License Amendment Request for Application to provide a new Technical Specification 3.7.5, Auxiliary Feedwater System, Condition G (EPID: L-2020-LLA-0176), dated August 17, 2020

Dear Commissioners and Staff:

In Reference 1, Pacific Gas and Electric Company (PG&E) submitted an exigent license amendment request to revise Technical Specification 3.7.5, Auxiliary Feedwater System. In Reference 2, PG&E responded to an NRC Staff request for additional information (RAI). In Reference 3, the NRC Staff provided an additional RAI via an e-mail, dated August 17, 2020. The Enclosure to this letter provides the PG&E responses to the Reference 3 RAI.

This letter does not contain new regulatory commitments (as defined by NEI 99-04).

A member of the STARS Alliance Callaway

• Diablo Canyon

• Palo Verde

• Wolf Creek

Document Control Desk PG&E Letter DCL-20-069 August 18, 2020 Page 2 If you have any questions or require additional information, please contact Mr. James Morris at (805) 545-4720.

I state under penalty of perjury that the foregoing is true and correct.

Executed on August 18, 2020.

Sincerely,

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Paula Gerfen Site Vice President kjse/51084143-14 Enclosure cc: Diablo Distribution cc/enc: Samson S. Lee, NRR Senior Project Manager Scott A. Morris, NRC Region IV Administrator Christopher W. Newport, NRC Senior Resident Inspector Gonzalo L. Perez, Branch Chief, California Department of Public Health A member of the STARS Alliance Callaway

• Diablo Canyon

• Palo Verde

• Wolf Creek

Enclosure PG&E Letter DCL-20-069 PG&E Response to NRC Request for Additional Information Regarding License Amendment Request 20-01, Exigent Request for Revision to Technical Specification 3.7.5, Auxiliary Feedwater System

References:

1. PG&E Letter DCL-20-066, License Amendment Request 20-01, Exigent Request for Revision to Technical Specification 3.7.5, Auxiliary Feedwater System, dated August 12, 2020, ADAMS Accession No. ML20225A303

2. PG&E Letter DCL-20-068, Response to NRC Request for Additional Information Regarding License Amendment Request 20-01, Exigent Request for Revision to Technical Specification 3.7.5, Auxiliary Feedwater System, dated August 16, 2020, ADAMS Accession No. ML20229A016

3. E-mail from NRC Senior Project Manager, Samson Lee, Diablo Canyon additional request for additional information: Exigent License Amendment Request for Application to provide a new Technical Specification 3.7.5, Auxiliary Feedwater System, Condition G (EPID:

L-2020-LLA-0176), dated August 17, 2020 NRC Request for Additional Information (RAI) #1:

Basis for higher corrosion rates at Unit 2 when compared to Unit 1

• Background. The August 16 submittal states Unit 2 has a higher corrosive environment compared to Unit 1 due to localized weather patterns concentrating on the Unit 2 side. The staff seeks clarification regarding how localized weather patterns are more aggressive at Unit 2 when compared to Unit 1. Corrosion in Marine Atmospheres (located in ASM Handbook, Volume 13C: Corrosion:

Environments and Industries) states that the atmospheric corrosion rates of carbon steel in a marine environment can be influenced by several factors such as distance from sea, location above sea level, direction and magnitude of air currents which transport droplets of corrosive seawater, etc. The staff also recognizing that the basis for a higher corrosive environment could be addressed through comparison of external loss of material rates; however, corrosion rate data was only provided for Unit 1 (2-8 mils/year).

• Request. Provide clarification regarding why Unit 2 has a higher corrosive environment when compared to Unit 1 through providing additional information regarding localized weather patterns and/or comparison of corrosion rate data.

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Enclosure PG&E Letter DCL-20-068 PG&E Response:

Pacific Gas and Electric Company (PG&E) utilizes the reference Corrosion in Marine Atmospheres (located in ASM International Handbook, Volume 13C: Corrosion:

Environments and Industries) that states the atmospheric corrosion rates of carbon steel in a marine environment can be influenced by several factors such as distance from sea, location above sea level, direction, and magnitude of air currents which transport droplets of corrosive seawater, etc. Different localized weather patterns exist at the Diablo Canyon Power Plant (DCPP) Units 1 and 2 due to differences in geometry of building arrangements and prevailing wind directions (i.e., different direction and magnitude of air currents between units), which create a higher corrosion atmosphere on DCPP Unit 2. Contamination monitoring of high voltage insulators in the Unit 2 transformer yard, directly adjacent to the Unit 2 pipe rack, determined the area to have a heavier contamination micro-climate due to the circulating water system outfall location, emergency diesel generator exhaust and wind tunnel created by the buildings.

Contamination includes deposits from sources such as the marine environment and adjacent diesel engine exhaust. This relative condition between the two units has been confirmed by visual observations of general corrosion during annual inspections of Units 1 and 2 pipe racks performed as part of the Pipe Rack Aging Management Program. This contrasts with the Unit 1 transformer yard, directly adjacent to the Unit 1 pipe rack, that is not subject to these influences. In addition, localized wetting associated with the use of the secondary steam system 10 percent atmospheric steam dump valves has occurred more frequently on DCPP Unit 2. Dry deposits of marine chlorides and other contaminants can be rewetted and migrate during such conditions, such as under insulation. A review of the Corrective Action Program identified on the order of twice as many condition reports documenting corrosion and coating conditions on the Unit 2 pipe rack versus Unit 1. The corrosion rate data provided for DCPP Unit 1 in the response to RAI number 10 in Reference 2 was based on the reference Corrosion in Marine Atmospheres for carbon steel in a marine environment.

NRC RAI #2:

Clarification regarding inspection methodology for the five pipe segments on Unit 1

• Background. The staff seeks clarification regarding the inspection methodology planned for the five pipe segments on Unit 1. The submittal states that ultrasonic testing methods were utilized during the Unit 2 inspections; however, the submittal also references walkdowns of Unit 1 piping conducted on July 25th and 26th. The staff notes that walkdowns are not capable of quantifying the extent of general and/or local outside metal loss patterns on the external surfaces of insulated piping.

• Request. Provide clarification regarding inspection methodology for the five pipe segments on Unit 1. If ultrasonic or other volumetric examination methods will not be utilized, state the basis for how the alternative methodologies can quantify the extent of general and/or local outside metal loss patterns on the external surfaces of insulated piping.

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Enclosure PG&E Letter DCL-20-069 PG&E Response:

The methodology that PG&E will use during the DCPP Unit 1 piping inspections is an inspection of the extent-of-condition areas on DCPP Unit 1 using the same process that was employed for DCPP Unit 2. Initial inspections will be performed by trained engineering personnel following insulation removal to determine initial pipe surface condition and to identify if corrosion product removal is needed to ascertain the extent of pipe wall degradation. Following corrosion product removal, using pit/depth gauges and scales as needed, an assessment of pipe condition with respect to remaining wall thickness will be made. Should any area show gross thinning or pitting from nominal outside diameter, then Engineering will initiate focused inspections of these identified areas by qualified personnel using ultrasonic testing methods, a pit/depth gauge, and if necessary, contour measurements and/or laser scanning. Piping areas found below the code minimum wall thickness will be fully characterized by Inservice Inspection group personnel. The results of the inspections will be entered into the DCPP Corrective Action Program and evaluated against a completed piping structural finite element analysis for determination of acceptability or repair.

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