ML20268B187

ASME Section XI Inservice Inspection Program, Proposed Inservice Inspection Alternative N1-I5-NDE-002, Response to Request for Additional Information

ML20268B187
Person / Time
Site:	North Anna
Issue date:	09/24/2020
From:	Mark D. Sartain Virginia Electric & Power Co (VEPCO)
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
20-340, N1-I5-NDE-002
Download: ML20268B187 (7)

Text

VIRGINIA ELECTRIC AND POWER COMPANY RICHMOND, VIRGINIA 23261 10 CFR 50.55a September 24, 2020 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555-0001 Serial No.:

NRA/ENC:

Docket No.:

License No.:

20-340 RO 50-338 NPF-4 VIRGINIA ELECTRIC AND POWER COMPANY (DOMINION ENERGY VIRGINIA)

NORTH ANNA POWER STATION UNIT 1 ASME SECTION XI INSERVICE INSPECTION PROGRAM PROPOSED INSERVICE INSPECTION ALTERNATIVE N1-I5-NDE-002 RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION By letter dated May 18, 2020 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML20140A239), Virginia Electric and Power Company (Dominion Energy Virginia} proposed an alternative to the requirements of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel (BPV) Code,Section XI for North Anna Power Station Unit 1 (NAPS1). Specifically, IWB-2420(b)1 Successive Inspections, requires a re-examination of the flaws identified in the fourth ISi interval, Third Period, B-N-1 examination on the interior surface of the reactor pressure vessel (RPV) during the next three inspection periods. While the B-N-1 examination is normally performed each period, only areas made accessible by removal of components are examined. An alternative was requested for B-N-1 examination of degraded cladding in areas only made accessible by the removal of the core barrel, an evolution normally taking place once per 10-year inspection interval.

In an August 25, 2020 e-mail from Mr. Ed Miller (NRC Senior Project Manager) to Ms.

Diane Aitken (Dominion Energy Virginia Corporate Licensing), the NRC technical staff requested additional information regarding the proposed alternative by September 28, 2020. Dominion's response to the NRC request for additional information is provided in the enclosure to this letter.

The Enterprise Project Identifier (EPID) referenced for this request is L-2020-LLR-0075.

Serial No.: 20-340 Docket No.: 50-338 RAI Response -Alternative Request N1-I5-NDE-002 Page 2 of 3 Please contact Erica N. Combs at 804-273-3386 if you have any questions regarding this submittal.

Sincerely, Mark D. Sartain Vice President - Nuclear Engineering & Fleet Support

Enclosure:

Response to NRC Request for Additional Information Proposed lnservice Inspection Alternative N1-I5-NDE-002 Commitments made by this letter: None

References:

1. Letter from Dominion Energy Virginia to NRC, "North Anna Power Station Unit 1 ASME Section XI lnservice Inspection Program, Proposed lnservice Inspection Alternative N1-I5-NDE-002," dated May 18, 2020. [ADAMS Accession No. ML20140A239]

2. Email from Ed Miller to Diane Aitken, dated August 25, 2020 8:21 AM,

Subject:

Draft RAI Request N 1-15-002.

Serial No.: 20-340 Docket No.: 50-338 RAI Response - Alternative Request N 1-I5-NDE-002 Page 3 of 3 cc:

Regional Administrator, Region II U.S. Nuclear Regulatory Commission Marquis One Tower 245 Peachtree Center Avenue, NE, Suite 1200 Atlanta, GA 30303-1257 Mr. G. E. Miller Senior Project Manager - North Anna Power Station U.S. Nuclear Regulatory Commission Mail Stop 09 E-3 One White Flint North 11555 Rockville Pike Rockville, MD 20852-2738 Mr. Marcus Harris Old Dominion Electric Cooperative Innsbrook Corporate Center 4201 Dominion Boulevard, Suite 300 Glen Allen, VA 23060 NRC Senior Resident Inspector North Anna Power Station

ENCLOSURE Response to NRC Request for Additional Information Proposed lnservice Inspection Alternative N1-I5-NDE-002 Virginia Electric and Power Company (Dominion Energy Virginia)

North Anna Power Station Unit 1

Serial No.20-340 Docket No. 50-338 Enclosure Page 1 of 3 RESPONSE TO NRC REQUEST FOR ADDITIONAL INFORMATION PROPOSED INSERVICE INSPECTION ALTERNATIVE N1-I6-NDE-002 By letter dated May 18, 2020 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML20140A239), Virginia Electric and Power Company (Dominion Energy Virginia) proposed an alternative to the requirements of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel (BPV) Code,Section XI for North Anna Power Station Unit 1 (NAPS1). Specifically, IWB-2420(b),

Successive Inspections, requires a re-examination of the flaws identified in the fourth ISi interval, Third Period, B-N-1 examination on the interior surface of the reactor pressure vessel (RPV) during the next three inspection periods. While the B-N-1 examination is normally performed each period, only areas made accessible by removal of components are examined. An alternative was requested for B-N-1 examination of degraded cladding in areas only made accessible by the removal of the core barrel, an evolution normally taking place once per 10-year inspection interval.

In an August 25, 2020 e-mail from Mr. Ed Miller (NRC Senior Project Manager) to Ms.

Diane Aitken (Dominion Energy Virginia Corporate Licensing), the NRC technical staff requested additional information regarding the proposed alternative by September 28, 2020. Dominion's response to the NRC request for additional information is provided in the enclosure to this letter.

The Enterprise Project Identifier (EPID) referenced for this request is L-2020-LLR-0075.

RAI 1

Request:

In calculation C-4523-00-02-P, an upper corrosion feature size of one inch in depth is assumed for this evaluation. It is assumed that the feature is localized. An estimate of the additional stress resulting from a one-inch deep local corrosion feature was made by assuming the stresses are primarily from bending due to a stud preload. The increase in stress of the reduced section was estimated by assuming the section acts as a beam in bending. A one-inch reduction in thickness for the lower shell at the transition to the bottom head was likewise assumed. Thus, the consideration of the geometric discontinuities resulted in an increase in the membrane plus bending stress for the upper corrosion feature and membrane stress for lower corrosion features. However, the geometric discontinuity due to the stress concentration should result in a peak stress at the corner of the assume 1.0-inch-deep corrosion features. Though Reference 15

Serial No.20-340 Docket No. 50-338 Enclosure Page 2 of 3 (Peterson, R. E., "Stress Concentration Factors", John Wiley & Sons, Inc. 1974) of the relief request, is cited for a stress concentration factor, it does not appear that a stress concentration factor was used in the calculation. Clarify whether calculation C-4523 02-P explicitly addresses the resulting peak stress due to the stress concentration at the comer of the geometric discontinuity of the assumed 1. 0-inch-deep corrosion features. If not, please justify its exclusion.

Response

Calculation C-4523-00-02-P explicitly applies a conservative stress concentration factor in the calculation of peak stress to account for the corner of the geometric discontinuity of the assumed 1.0-inch-deep corrosion features. The peak stress at the assumed corrosion features is evaluated in the calculation using ASME Code Section Ill rules for fatigue. As such, a stress concentration factor (i.e., fatigue strength reduction factor) of 4.0 is used for both the upper and lower corrosion features. The stress concentration factor value of 4.0 is taken from Assumption 7 of the calculation, which states: "The effect of the corrosion feature on fatigue is considered by assuming a fatigue strength reduction factor of 4.0. A value of 4.0 is used for locations such as the root of threads [5, Paragraph N-416.2(b)(4)] and is considered a conservative estimate." Reference 5 is the ASME Boiler and Pressure Vessel Code, Section Ill, 1968 Edition with Addenda through Winter 1968.

The peak stresses due to stress concentration for the upper and lower corrosion features are evaluated in the calculation in Section 5.1.3.1 and Section 5.2, respectively. In each case, the stress amplitude excluding local discontinuities is multiplied by a stress concentration factor of 4.0 to calculate the total stress amplitude. The allowable number of cycles at the calculated total stress amplitude is then compared to the design cycles, and the two values are used to calculate a fatigue usage factor that includes the effect of the corrosion feature. The calculated fatigue usage values at both corrosion features are well below the allowable value of 1.0.

As indicated above, a stress concentration factor was used in the cited calculation in recognition of each corrosion feature.

The above information has previously been provided in Reference 1, Attachment 3.

REFERENCES Serial No.20-340 Docket No. 50-338 Enclosure Page 3 of 3

1. Letter from Dominion to NRC, "North Anna Power Station Unit 1, ASME Section XI lnservice Inspection Program, Proposed lnservice Inspection Alternative N1-I5-NDE-002," dated May 18, 2020 (S/N 19-156). [ADAMS Accession No. ML20140A239]