ML17090A429

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ASME Section XI Inservice Inspection Program Proposed - Inservice Inspection Alternative N1-14-NDE-010 and N2-14-NDE-005
ML17090A429
Person / Time
Site: North Anna  Dominion icon.png
Issue date: 03/27/2017
From: Mark D. Sartain
Virginia Electric & Power Co (VEPCO)
To:
Document Control Desk, Office of Nuclear Reactor Regulation
References
17-079
Download: ML17090A429 (14)
v • d • e


Text

10 CFR 50.55a VIRGINIA ELECTRIC AND POWER COMPANY RICHMOND, VIRGINIA 2326I March 27, 2017 United States Nuclear Regulatory Commission Serial No.17-079 Attention: Document Control Desk NAPS/MPW RO Washington, D.C. 20555 Docket Nos. 50-338 50-339 License Nos. NPF-4 NPF-7 VIRGINIA ELECTRIC AND POWER COMPANY (DOMINION)

NORTH ANNA POWER STATION UNITS 1 AND 2 ASME SECTION XI INSERVICE INSPECTION PROGRAM PROPOSED INSERVICE INSPECTION ALTERNATIVE N1-14-NDE-010

';-P.ROPOSED INSERVICE INSPECTION ALTERNATIVE N2-14-NDE-005 In accordance with 10 CFR 50.55a(z)(1 ), Dominion hereby requests Nuclear Regulatory Commission (NRC) approval of proposed inservice inspection (ISi) alternatives N1-14-NDE-010 and N2-14-NDE-005. The requests are to extend the interval for reactor vessel nozzle welds, Category 8-F pressure retaining welds from 10 years to 20 years in accordance with WCAP-17236-NP-A, Revision 0, Risk-Informed Extension of the Reactor Vessel Nozzle lnservice Inspection Interval. The proposed alternatives are provided in Attachments 1 and 2.

Dominion requests approval of the proposed alternatives by March 1, 2018. If you have any questions, please contact Mr. Donald Taylor at (540) 894-2100.

Sincerely,

~*-

Mark Sartain Vice President Nuclear Engineering and Fleet Support This letter contains no NRC commitments.

Attachments

1. N1-14-NDE-010 Proposed Alternative for North Anna Unit 1 Reactor Vessel Nozzle Weld Examinations Extension
2. N2-14-NDE-005 Proposed Alternative for North Anna Unit 2 Reactor Vessel Nozzle Weld Examinations Extension

Serial No.17-079 Docket Nos. 50-338/339 NAPS 1 and 2 RV Nozzle Weld Examinations Extension Page 2 of 2 cc: U.S. Nuclear Regulatory Commission Region II Marquis One Tower 245 Peachtree Center Avenue, NE Suite 1200 Atlanta, GA 30303-1257 Mr. J. E. Reasor, Jr.

Old Dominion Electric Cooperative Innsbrook Corporate Center 4201 Dominion Blvd.

Suite 300 Glen Allen, Virginia 23060 NRC Senior Resident Inspector North Anna Power Station Ms. B. L. Mozafari NRC Project Manager-North Anna U. S. Nuclear Regulatory Commission One White Flint North Mail Stop 0-8 G9A 11555 Rockville Pike Rockville, Maryland 20852 Ms. K. R. Cotton-Gross NRC Project Manager-Surry U. S. Nuclear Regulatory Commission One White Flint North Mail Stop 0-8 G9A 11555 Rockville Pike Rockville, Maryland 20852

Serial No.17-079 Docket No. 50-338 NAPS Unit 1 RV Nozzle Weld Examinations Extension Attachment 1 - Page 1 of 6 ATTACHMENT 1 N1-14-NDE-010 PROPOSED ALTERNATIVE FOR NORTH ANNA UNIT 1 REACTOR VESSEL NOZZLE WELD EXAMINATIONS EXTENSION VIRGINIA ELECTRIC AND POWER COMPANY (DOMINION)

NORTH ANNA POWER STATION UNIT 1

Serial No.17-079 Docket No. 50-338 NAPS Unit 1 RV Nozzle Weld Examinations Extension Attachment 1 - Page 2 of 6 N1-14-NDE-010 Proposed Alternative for North Anna Unit 1 Reactor Vessel Nozzle Weld Examinations Extension In Accordance with 10 CFR 50.55a(z)(1)

-- Alternative Provides Acceptable Level of Quality and Safety --

1.0 ASME CODE COMPONENT(S) AFFECTED The affected components are the North Anna Unit 1 reactor vessel (RV) nozzles; specifically, the following American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel (BPV) Code,Section XI (Reference 1) examination category and item number covering examinations of the RV nozzles. This examination category and item number are from IWB-2500 and Table IWB-2500-1 of the ASME BPV Code,Section XI.

Category B-F welds are defined as "Pressure Retaining Dissimilar Metal Welds in Vessel Nozzles." North Anna Power Station Unit 1 (NAPS 1) has Westinghouse Nuclear Steam Supply System (NSSS) RV nozzle-to-piping weld design configurations with a single stainless steel dissimilar metal weld and no safe-end. The most appropriate categorization for these NAPS 1 welds in the applicable code edition and addenda is item number B5.10, which is defined as RV nozzle-to-safe-end butt welds.

Examination I. Category Item No. Description B-F B5.10 NPS 4 (ON 100) or Larger Nozzle-to-Safe End Butt Welds (Throughout this request the above examination categories are referred to as "the subject examinations" and the ASME BPV Code,Section XI, is referred to as "the Code.")

2.0 APPLICABLE CODE EDITION AND ADDENDA The NAPS 1 applicable Code for the fourth 10-year inservice inspection (ISi) interval and the ISi program is the 2004 Edition of Section XI with no Addenda (Reference 1). The NAPS 1 fourth interval started May 1, 2009 and ends April 30, 2019. The NAPS 1 fifth interval starts May 1, 2019 and ends April 30, 2029.

3.0 APPLICABLE CODE REQUIREMENT IWB-2412, Inspection Program B, requires volumetric examination of all RV nozzle-to-piping butt welds identified in Table IWB-2500-1 once each 10-year interval. The NAPS 1 fourth 10-year ISi interval is scheduled to end on April 30, 2019. The applicable Code for the fifth 10-year ISi interval will be selected in accordance with the requirements of 10 CFR 50.55a.

4.0 REASON FOR REQUEST An alternative is requested from the requirement of IWB-2412, Inspection Program B, that volumetric examination of all RV nozzle-to-piping Examination Category B-F butt welds be

Serial No.17-079 Docket No. 50-338 NAPS Unit 1 RV Nozzle Weld Examinations Extension Attachment 1 - Page 3 of 6 performed once each 10-year interval. Extension of the interval between the subject examinations from 10 years to up to 20 years will result in a reduction in person-rem exposure and examination costs.

5.0 PROPOSED ALTERNATIVE AND BASIS FOR USE Dominion proposes not to perform the Code required volumetric examination of the NAPS 1 RV nozzle-to-piping Examination Category B-F butt welds for the fourth inservice inspection, currently scheduled for spring 2018. Dominion will perform the Code required subject examinations for NAPS 1 in the fifth inservice inspection interval in the fall of 2028, before the end of the interval on April 30, 2029. The dates in the latest implementation plan, PWROG Letter OG-10-238 (Reference 2), reflect no implementation of the extended inservice inspection interval for NAPS 1; therefore, the proposed inspection date for NAPS 1 is a deviation from the schedule presented in Reference 2. Despite this deviation, the proposed ISi interval extension for NAPS 1 would not result in any significant inspection gaps where examinations of RV nozzle-to-piping welds would not take place.

In accordance with 10 CFR 50.55a(z)(1), an alternate inspection interval is requested on the basis that the proposed new interval would result in a negligible change-in-risk using the risk criteria specified in Regulatory Guide (RG) 1.174 (Reference 3).

The methodology used to determine the change-in-risk from the proposed new interval is based on that defined in the study WCAP-17236-NP-A, Revision 0, "Risk-Informed Extension of the Reactor Vessel Nozzle lnservice Inspection Interval" .(Reference 4). This study focuses on risk assessments of Examination Category B-F and B-J RV nozzle-to-piping welds. The evaluation for NAPS 1 was performed following the four regulatory evaluation steps defined in Section 2 of Reference 4. The evaluation addresses the conditions and limitations as defined by the safety evaluation report (SER) for Reference 2 and is compared to the change-in-risk criteria defined in RG 1.174 (Reference 3) and Code Case (CC) N-716 (Reference 5).

Step 1: Nozzle weld Configuration Type NAPS 1 has Westinghouse NSSS RV nozzle-to-piping weld design configurations with a single stainless steel dissimilar metal weld and no safe-end. This design configuration is shown as Type C in Table 4-1 of Reference 4.

Step 2: Previous lnservice Inspection Results The latest examinations for the NAPS 1 RV nozzle-to-piping welds demonstrated that there were no recordable indications. Therefore, NAPS Unit 1 meets the implementation requirements of having no more than one inside diameter (ID) surface flaw in each RV nozzle-to-piping weld as described in Section 2.2 of Reference 4.

Serial No.17-079 Docket No. 50-338 NAPS Unit 1 RV Nozzle Weld Examinations Extension Attachment 1 - Page 4 of 6 Step 3: Change-In-Risk Evaluation Following the calculation template provided in Table 2-1 of Reference 4, the change-in-risk associated with extending the ISi interval for the RV nozzle welds has been calculated and is provided in Table 1. The change-in-risk evaluation used the 60-year change-in-failure frequencies without leak detection from Table 3-5 (which are the maximum values) of Reference 4 and plant-specific conditional core damage probability (CCDP) and conditional large early release probability (CLERP) values. The change-in-risk in terms of change in core damage frequency (b.CDF) and change in large early release frequency (b.LERF) is calculated for four failure modes related to a loss-of-coolant accident (LOCA): small-small LOCA (SSLGCA), small LOCA (SLOCA), medium LOCA (MLOCA), and large LOCA (LLOCA). The total change-in-risk is the summation of the change-in-risk for each failure mode for each weld (6 welds total).

Table 1: NAPS 1 Change-in-Risk Bounding Change in Failure ACDF ALE RF Failure Mode CCDP CLE RP Frequency (w/o (/year) (/year) leak detection)

Outlet Nozzles SSLOCA 1.18E-07 4.55E-05 5.37E-12 2.55E-06 3.01 E-13 SLOCA 1.18E-07 2.27E-04 2.68E-11 3.97E-05 4.68E-12 MLOCA 1.18E-07 5.05E-04 5.96E-11 4.46E-05 5.26E-12 LLOCA 1.18E-07 9.27E-04 1.09E-10 4.62E-05 5.45E-12

  1. of Welds Examined 3 Total bCDF 6.03E-10 Total bLERF 4.71E-11 Inlet Nozzles SSLOCA 1.13E-07 4.55E-05 5.14E-12 2.55E-06 2.88E-13 SLOCA 1.13E-07 2.27E-04 2.57E-11 3.97E-05 4.49E-12 MLOCA 1.23E-07 5.05E-04 6.21 E-11 4.46E-05 5.49E-12 LLOCA 1.23E-07 9.27E-04 1.14E-10 4.62E-05 5.68E-12
  1. of Welds Examined 3 Total bCDF 6.21E-10 Total bLERF 4.78E-11 All Nozzles Total Change-in-Risk Results Total bCDF 1.22E-09 Total bLERF 9.49E-11 These values for NAPS 1 meet the RG 1.174 (Reference 3) acceptance criteria for an acceptably small change-in-risk because total plant b.CDF < 1E-06/year and b.LERF

< 1E-07/year.

Step 4: Effect on Risk-informed lnservice Inspection Program The impact on the NAPS ASME CC N-716 (Reference 5) Risk-Informed (RI) ISi program associated with extending the ISi interval for the RV nozzles has been calculated and is provided in Table 2. The maximum change-in-failure frequency values with leak detection for

~

Serial No.17-079 Docket No. 50-338 NAPS Unit 1 RV Nozzle Weld Examinations Extension Attachment 1 - Page 5 of 6 the inlet and outlet nozzles are multiplied by the maximum NAPS 1 CCDP and CLERP values to calculate the change-in-risk (L.\CDF and L.\LERF). These values are multiplied by the number of inlet and outlet nozzles to determine the total L.\CDF and L.\LERF associated with extending the ISi interval, which is then added to the reactor coolant (RC) system and total plant change-in-risk results of the RI-ISi program.

Table 2: Effects of RV Nozzle-to-Piping Weld ISi Interval Extension on NAPS 1 RI-ISi Program Maximum Failure Change in ACDF ALE RF CCDP CLE RP Mode Failure (/year) (/year) 1 Frequency Outlet Nozzles SLOCA 4.49E-09 9.27E-04 4.16E-12 6.95E-05 3.12E-13

  1. of Welds Examined 3 Total ilCDF 1.25E-11 Total ilLERF 9.36E-13 Inlet Nozzles LLOCA 3.61 E-09 9.27E-04 3.35E-12 6.95E-05 2.51E-13
  1. of Welds Examined 3 Total ilCDF 1.00E-11 Total ilLERF 7.53E-13 All Nozzles Nozzle Change-in-Risk Results 2.25E-11 1.69E-12 RC System Change in Risk -2.0SE-09 -1.56E-10 NevlRC Sy$te,m Change in Ri~k Plant Change in Risk 9.25E-09 6.94E-10 Notes:
1. Maximum change in failure frequency values with leak detection from Table 3-5 of WCAP-17236-NP-A [4].

The updated NAPS 1 RC system changes in risk meet the CC N-716 acceptance criteria for an insignificant increase in risk, which is L.\CDF < 1E-07/year and L.\LERF < 1 E-08/year. In addition, the updated NAPS 1 total change-in-risk (all systems) meets the criteria of RG 1.174 (Reference 3) for an acceptably small change-in-risk, which is L.\CDF < 1 E-06/year and L.\LERF

< 1E-07/year.

Therefore, implementation of the RV nozzle weld ISi interval extension for the NAPS 1 ASME Category B-F nozzle-to-piping welds satisfies the acceptable change-in-risk criteria per CC N-716 (Reference 5).

6.0 DURATION OF PROPOSED ALTERNATIVE This request is applicable to the North Anna Unit 1 ISi program for the fourth and fifth 10-year inspection intervals.

Serial No.17-079 Docket No. 50-338 NAPS Unit 1 RV Nozzle Weld Examinations Extension Attachment 1 - Page 6 of 6

7.0 REFERENCES

1. ASME Boiler and Pressure Vessel Code,Section XI, 2004 Edition with No Addenda, ASME International. *
2. PWR Owners Group Letter, OG-10-238, "Revision to the Revised Plan for Plant Specific Implementation of Extended lnservice Inspection Interval per WCAP-16168-NP, Revision 1,

'Risk-Informed Extension of the Reactor Vessel In-Service Inspection Interval' PA-MSC-0120," July 12, 2010.

3. Regulatory Guide 1.174, Revision 2, "An Approach for Using Probabilistic Risk Assessment in Risk-Informed Decisions on Plant-Specific Changes to the Licensing Basis," November 2011 (ADAMS Accession Number ML100910006).
4. Westinghouse Report, WCAP-17236-NP-A, Revision 0, "Risk-Informed Extension of the Reactor Vessel Nozzle lnservice Inspection Interval," July 2012 (ADAMS Accession Number ML12215A043).
5. ASME Boiler and Pressure Vessel Code, Case N-716, "Alternative Piping Classification and Examination Requirements,"Section XI, Division 1, 2006, approved for use in the 4th Inspection Interval per Relief Request N1-14-Rl-001 (ADAMS Accession Number ML110050003, 11/23/2010).

Serial No.17-079 Docket No. 50-339 NAPS Unit 2 RV Nozzle Weld Examinations Extension Attachment 2 - Page 1 of 6 ATTACHMENT 2 N2-14-NDE-005 PROPOSED ALTERNATIVE FOR NORTH ANNA UNIT 2 REACTOR VESSEL NOZZLE WELD EXAMINATIONS EXTENSION VIRGINIA ELECTRIC AND POWER COMPANY (DOMINION)

NORTH ANNA POWER STATION UNIT 2

Serial No.17-079 Docket No. 50-339 NAPS Unit 2 RV Nozzle Weld Examinations Extension Attachment 2 - Page 2 of 6 N2-14-NDE-005 Proposed Alternative for North Anna Unit 2 Reactor Vessel Nozzle Weld Examinations Extension In Accordance with 10 CFR 50.55a(z)(1)

-- Alternative Provides Acceptable Level of Quality and Safety --

1.0 ASME CODE COMPONENT(S) AFFECTED The affected components are the North Anna Unit 2 reactor vessel (RV) nozzles; specifically, the following American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel (BPV) Code,Section XI (Reference 1) examination category and item number covering examinations of the RV nozzles. This examination category and item number are from IWB-2500 and Table IWB-2500-1 of the ASME BPV Code,Section XI.

Category B-F welds are defined as "Pressure Retaining Dissimilar Metal Welds in Vessel Nozzles." North Anna Power Station Unit 2 (NAPS 2) has Westinghouse Nuclear Steam Supply System (NSSS) RV nozzle-to-piping weld design configurations with a single stainless steel dissimilar metal weld and no safe-end. The most appropriate categorization for these NAPS 2 I '

welds in the applicable code edition and addenda is item number B5.10, which is defined as RV I

nozzle-to-safe-end butt welds.

1, I: Examination Category Item No Description B-F B5.10 NPS 4 (ON 100) or Larger Nozzle-to-Safe End Butt Welds (Throughout this request the above examination categories are referred to as "the subject examinations" and the ASME BPV Code,Section XI, is referred to as "the Code.")

2.0 APPLICABLE CODE EDITION AND ADDENDA The NAPS 2 applicable Code for the fourth 10-year inservice inspection (ISi) interval and the ISi program is the 2004 Edition of Section XI with no Addenda (Reference 1). The NAPS 2 fourth interval started December 14, 2010 and ends December 13, 2020. The NAPS 2 fifth interval starts December 14, 2020 and ends December 13, 2030.

3.0 APPLICABLE CODE REQUIREMENT IWB-2412, Inspection Program B, requires volumetric examination of all RV nozzle-to-piping butt welds identified in Table IWB-2500-1 once each 10-year interval. The NAPS 2 fourth 10-year ISi interval is scheduled to end on December 13, 2020. The applicable Code for the fifth 10-year ISi interval will be selected in accordance with the requirements of 10 CFR 50.55a.

4.0 REASON FOR REQUEST An alternative is requested from the requirement of IWB-2412, Inspection Program B, that volumetric examination of all RV nozzle-to-piping Examination Category B-F butt welds be

Serial No.17-079 Docket No. 50-339 NAPS Unit 2 RV Nozzle Weld Examinations Extension Attachment 2 - Page 3 of 6 performed once each 10-year interval. Extension of the interval between the subject examinations from 10 years to up to 20 years will result in a reduction in person-rem exposure and examination costs.

5.0 PROPOSED ALTERNATIVE AND BASIS FOR USE Dominion proposes not to perform the Code required volumetric examination of the NAPS 2 RV nozzle-to-piping Examination Category 8-F butt welds for the fourth inservice inspection, currently scheduled for fall 2020. Dominion will perform the Code required subject examinations for NAPS 2 in the fifth inservice inspection interval in the fall of 2029, before the end of the interval on December 13, 2030. The dates in the latest implementation plan, PWROG Letter OG-10-238 (Reference 2), reflect no implementation of the extended inservice inspection interval for NAPS 2; therefore, the proposed inspection date for NAPS 2 is a deviation from the schedule presented in Reference 2. Despite this deviation, the proposed ISi interval extension for NAPS 2 would not result in any significant inspection gaps where examinations of RV nozzle-to-piping welds would not take place.

In accordance with 10 CFR 50.55a(z)(1), an alternate inspection interval is requested on the basis that the proposed new interval would result in a negligible change-in-risk using the risk criteria specified in Regulatory Guide (RG) 1.174 (Reference 3).

The methodology used to determine the change-in-risk from the proposed new interval is based on that defined in the study WCAP- 17236-NP-A, Revision 0, "Risk-Informed Extension of the Reactor Vessel Nozzle lnservice Inspection Interval" (Reference 4). This study focuses on risk assessments of Examination Category 8-F and 8-J RV nozzle-to-piping welds. The evaluation for NAPS 2 was performed following the four regulatory evaluation steps defined in Section 2 of Reference 4. The evaluation addresses the conditions and limitations as defined by the safety evaluation report (SER) for Reference 2 and is compared to the change-in-risk criteria defined in RG 1.174 (Reference 3) and Code Case (CC) N-716 (Reference 5).

Step 1: Nozzle weld Configuration Type NAPS 2 has Westinghouse NSSS RV nozzle-to-piping weld design configurations with a single stainless steel dissimilar metal weld and no safe-end. This design configuration is shown as Type C in Table 4-1 of Reference 4.

Step 2: Previous lnservice Inspection Results The latest examinations for the NAPS 2 RV nozzle-to-piping welds demonstrated that there were no recordable indications. Therefore, NAPS 2 meets the implementation requirements of having no more than one inside diameter (ID) surface flaw in each RV nozzle-to-piping weld as described in Section 2.2 of Reference 4.

Serial No.17-079 Docket No. 50-339 NAPS Unit 2 RV Nozzle Weld Examinations Extension Attachment 2 - Page 4 of 6 Step 3: Change-In-Risk Evaluation Following the calculation template provided in Table 2-1 of Reference 4, the change-in-risk associated with extending the ISi interval for the RV nozzle welds has been calculated and is provided in Table 1. The change-in-risk evaluation used the 60-year change-in-failure frequencies without leak detection from Table 3-5 (which are the maximum values) of Reference 4 and plant-specific conditional core damage probability (CCDP) and conditional large early release probability (CLERP) values. The change-in-risk in terms of change in core damage frequency (L\CDF) and change in large early release frequency (L\LERF) is calculated for four failure modes related to a loss-of-coolant accident (LOCA): small-small LOCA (SSLOCA), small LOCA (SLOCA), medium LOCA (MLOCA), and large LOCA (LLOCA). The total change-in-risk is the summation of the change-in-risk for each failure mode for each weld (6 welds total).

Table 1: NAPS 2 Change-in-Risk Bounding Change in Failure A.CDF A.LERF Failure Mode CCDP CLE RP Frequency (w/o (/year) (/year) leak detection)

Outlet Nozzles SSLOCA 1.18E-07 4.12E-05 4.86E-12 1.70E-06 2.01E-13 SLOCA 1.18E-07 2.17E-04 2.56E-11 3.87E-05 4.57E-12 MLOCA 1.18E-07 4.35E-04 5.13E-11 4.30E-05 5.07E-12 LLOCA 1.18E-07 9.02E-04 1.06E-10 4.35E-05 5.13E-12

  1. of Welds Examined 3 Total b.CDF 5.65E-10 Total b.LERF 4.49E-11 Inlet Nozzles SSLOCA 1.13E-07 4.12E-05 4.66E-12 1.70E-06 1.92E-13 SLOCA 1.13E-07 2.17E-04 2.45E-11 3.87E-05 4.37E-12 MLOCA 1.23E-07 4.35E-04 5.35E-11 4.30E-05 5.29E-12 LLOCA 1.23E-07 9.02E-04 1.11E-10 4.35E-05 5.35E-12
  1. of Welds Examined 3 Total b.CDF 5.81E-10 Total b.LERF 4.56E-11 All Nozzles Total Change-in-Risk Results Total b.CDF 1.15E-09 Total b.LERF 9.05E-11 These values for NAPS 2 meet the RG 1.174 (Reference 3) acceptance criteria for an acceptably small change-in-risk because total plant L\CDF < 1E-06/year and L\LERF

< 1E-07/year.

Step 4: Effect on Risk-informed lnservice Inspection Program The impact on the NAPS ASME CC N-716 (Reference 5) Risk-Informed (RI) ISi program associated with extending the ISi interval for the RV nozzles has been calculated and is provided in Table 2. The maximum change-in-failure frequency values with leak detection for

Serial No.17-079 Docket No. 50-339 NAPS Unit 2. RV Nozzle Weld Examinations Extension Attachment 2 - Page 5 of 6 the inlet and outlet nozzles are multiplied by the maximum NAPS 2 CCDP and CLERP values to calculate the change-in-risk (L\CDF and L\LERF). These values are multiplied by the number of inlet and outlet nozzles to determine the total L\CDF and L\LERF associated with extending the ISi interval, which is then added to the reactor coolant (RC) system and total plant change-in-risk results of the RI-ISi program.

  • Table 2: Effects of RV Nozzle-to-Piping Weld ISi Interval Extension on NAPS 2 RI-ISi Program Maximum Failure Change in ACDF ALE RF CCDP CLE RP Mode Failure (/year) (/year).

1 Frequency Outlet Nozzles SLOCA 4.49E-09 9.02E-04 4.05E-12 6.95E-05 3.12E-13

  1. of Welds Examined 3 Total LlCDF 1.21E-11 Total LlLERF 9.36E-13 Inlet Nozzles LLOCA 3.61 E-09 9.02E-04 3.26E-12 6.95E-05 2.51E-13
  1. of Welds Examined 3 Total LlCDF 9.77E-12 .Total LlLERF 7.53E-13 All Nozzles Nozzle Change-in-Risk Results 2.19E-11 1.69E-12 RC System Change in Risk -3.30E-09 -2.54E-10

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Plant Change in Risk 8.77E-09 6.75E-10 1:. :New e1~11t'phangiJn RI~~* . ::*. !:?>>'( ';*":.:;;*.;:;:<. *>::s:19eto9 *:; ,<;. . '.~i;>~~[,:.;~* 5::'.,' ; );~~;77~1r1*9 \;i

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, "'>'" .* , ..* ' "., , < **~

Notes:

1. Maximum change in failure frequency values with leak detection from Table 3-5 of WCAP-17236-NP-A [4].

The updated NAPS 2 RC system changes in risk meet the CC N-716 acceptance criteria for an insignificant increase in risk, which is L\CDF < 1E-07/year and L\LERF < 1E-08/year. In addition, the updated NAPS 2 total change-in-risk (all systems) meets the criteria of RG 1.174 (Reference 3) for an acceptably small change-in-risk, which is L\CDF < 1E-06/year and L\LERF

< 1E-07/year.

Therefore, implementation of the RV nozzle weld ISi interval extension for the NAPS 2 ASME Category B-F nozzle-to-piping welds satisfies the acceptable change-in-risk criteria per CC N-716 (Reference 5).

6.0 DURATION OF PROPOSED ALTERNATIVE This request is applicable to the North Anna Unit 2 ISi program for the fourth and fifth 10-year inspection intervals .

  • 1'

Serial No.17-079 Docket No. 50-339 NAPS Unit 2 RV Nozzle Weld Examinations Extension Attachment 2 - Page 6 of 6

7.0 REFERENCES

1. ASME Boiler and Pressure Vessel Code,Section XI, 2004 Edition with No Addenda, ASME International.
2. PWR Owners Group Letter, OG-10-238, "Revision to the Revised Plan for Plant Specific Implementation of Extended lnservice Inspection Interval per WCAP-16168-NP, Revision 1,

'Risk-Informed Extension of the Reactor Vessel In-Service Inspection Interval' PA-MSC-0120,"

July 12,, 2010.

3. Regulatory Guide 1.174, Revision 2, "An Approach for Using Probabilistic Risk Assessment in Risk-Informed Decisions on Plant-Specific Changes to the Licensing Basis," November 2011 (ADAMS Accession Number ML100910006).
4. Westinghouse Report, WCAP-17236-NP-A, Revision 0, "Risk-Informed Extension of the Reactor Vessel Nozzle lnservice Inspection Interval," July 2012 (ADAMS Accession Number ML12215A043).
5. ASME Boiler and Pressure Vessel Code, Case N-716, "Alternative Piping Classification and Examination Requirements,"Section XI, Division 1, 2006, approved for use in the 4th Inspection Interval per Relief Request N2-14-Rl-001 (ADAMS Accession Number ML110050003, 11/23/2010).
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