ML15096A143
| ML15096A143 | |
| Person / Time | |
|---|---|
| Site: | Seabrook  |
| Issue date: | 07/28/2015 |
| From: | John Lamb Plant Licensing Branch 1 |
| To: | Dean Curtland NextEra Energy Seabrook |
| Lamb J, NRR/DORL/LPLI-2, 415-3100 | |
| Shared Package | |
| ML15205A334 | List: |
| References | |
| TAC MF4576 | |
| Download: ML15096A143 (29) | |
Text
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 Mr. Dean Curtland Vice President, Seabrook Nuclear Plant c/o Mr. Michael Ossing NextEra Energy Seabrook, LLC P.O. Box 300 Seabrook, NH 0387 4 July 28, 2015
SUBJECT:
SEABROOK STATION, UNIT NO. 1, EXEMPTION FROM SPECIFIC REQUIREMENTS OF 10 CFR PART 50, APPENDIX G, AND 10 CFR 50.60 (TAC NO. MF4576)
Dear Mr. Curtland:
The U.S. Nuclear Regulatory Commission has approved the enclosed exemption from specific requirements of Title 10 of the Code of Federal Regulations (10 CFR) Part 50, Appendix G, and 10 CFR 50.60, for the Seabrook Station, Unit No. 1. This action is in response to your application dated July 24, 2014, as supplemented by letters dated March 9, April 24, and June 24, 2015, that requested an exemption from specific requirements of 10 CFR Part 50, Appendix G, Table 1, Footnote 2, to allow the use of an alternate methodology contained in WCAP-17444-P, Revision 0, "Reactor Vessel Closure HeadNessel Flange Requirements Evaluation for Seabrook Unit 1."
A copy of the exemption and safety evaluation are enclosed. The exemption has been forwarded to the Office of the Federal Register for publication.
Docket No. 50-443
Enclosures:
- 1. Exemption
- 2. Safety Evaluation cc w/enclosures: Distribution via Listserv n G. Lamb, Senior Project Manager nt Licensing Branch 1-2 ivision of Operating Reactor Licensing Office of Nuclear Reactor Regulation
ENCLOSURE1 FEDERAL REGISTER NOTICE Exemption Seabrook Station, Unit 1 Docket No. 50-443
[7590-01-P]
NUCLEAR REGULATORY COMMISSION
[Docket No. 50-443; NRC-2015-NextEra Energy Seabrook, LLC, Seabrook Station, Unit 1 AGENCY: Nuclear Regulatory Commission.
ACTION: Exemption; issuance.
SUMMARY
- The U.S. Nuclear Regulatory Commission (NRC) is issuing an exemption in response to a July 24, 2014, request from NextEra Energy Seabrook, LLC (NextEra or the licensee), from specific requirements of Title 1 O of the Code of Federal Regulations (1 O CFR),
Part 50, Appendix G, "Fracture Toughness Requirements," as they pertain to the establishment of minimum temperature requirements, for all modes of operation, based on the material properties of the material of the reactor pressure vessel (RPV) closure flange region that is highly stressed by the bolt preload.
ADDRESSES: Please refer to Docket ID NRC-2015-when contacting the NRC about the availability of information regarding this document. You may obtain publicly-available information related to this document using any of the following methods:
Federal Rulemaking Web Site: Go to http://www.requlations.gov and search for Docket ID NRC-2015-
. Address questions about NRC dockets to Carol Gallagher; telephone:
301-415-3463; e-mail: Carol.Gallaqher@nrc.gov. For technical questions, contact the individual listed in the FOR FURTHER INFORMATION CONTACT section of this document.
NRC's Agencywide Documents Access and Management System (ADAMS):
You may obtain publicly-available documents online in the ADAMS Public Documents collection at http://www.nrc.gov/reading-rm/adams.html. To begin the search, select "ADAMS Public Documents" and then select "Begin Web-based ADAMS Search." For problems with ADAMS, please contact the NRC's Public Document Room (PDR) reference staff at 1-800-397-4209, 301-415-4737, or by e-mail to pdr.resource@nrc.gov. The ADAMS accession number for each document referenced in this document (if that document is available in ADAMS) is provided the first time that a document is referenced.
NRC's PDR: You may examine and purchase copies of public documents at the NRC's PDR, Room 01-F21, One White Flint North, 11555 Rockville Pike, Rockville, Maryland 20852.
FOR FURTHER INFORMATION CONTACT: John G. Lamb, Office of Nuclear Reactor Regulation, telephone: 301-415-3100, e-mail: John.Lamb@nrc.gov; U.S. Nuclear Regulatory Commission, Washington DC 20555-0001.
SUPPLEMENTARY INFORMATION:
I. Background.
NextEra is the holder of Facility Operating License No. NPF-86, which authorizes operation of the Seabrook Station, Unit No. 1 (Seabrook).
The Seabrook facility consists of a pressurized-water reactor located in Rockingham County, New Hampshire.
II. Request/Action.
By letter dated July 24, 2014 (ADAMS Accession No. ML14216A404), as supplemented by letters dated March 9, April 24, and June 24, 2015 (ADAMS Accession Nos. ML15072A023, ML15125A140, and ML15181A262, respectively), the licensee requested an exemption from 10 CFR 50.60, "Acceptance criteria for fracture prevention measures for lightwater nuclear power reactors for normal operation," pursuant to 10 CFR 50.12, "Specific exemptions."
1 O CFR Part 50, Appendix G requires that pressure-temperature (P-T) limits be established for RPVs during normal operating and hydrostatic or leak rate testing conditions.
Specifically, 1 O CFR Part 50, Appendix G states that "[t]he minimum temperature requirements... pertain to the controlling material, which is either the material in the closure flange or the material in the beltline region with the highest reference temperature.... the minimum temperature requirements and the controlling material depend on the operating condition (i.e., hydrostatic pressure and leak tests, or normal operation including anticipated normal operational occurrences), the vessel pressure, whether fuel is in the vessel, and whether the core is critical. The metal temperature of the controlling material, in the region of the controlling material which has the least favorable combination of stress and temperature, must exceed the appropriate minimum temperature requirement for the condition and pressure of the vessel specified in Table 1 [of 10 CFR Part 50, Appendix G]." Footnote 2 to Table 1 in 10 CFR Part 50, Appendix G specifies that RPV minimum temperature requirements related to RPV closure flange considerations shall be based on "[t]he highest reference temperature of the material in the closure flange region that is highly stressed by bolt preload."
By letter dated July 24, 2014, NextEra submitted a license amendment request (LAR) to implement a revision of the P-T operating limits for Seabrook. In requesting the revisions to the P-T operating limits, the licensee referenced a topical report with a methodology that did not meet some of the requirements of 10 CFR Part 50, Appendix G, thus requiring the exemption pursuant to 1 O CFR 50.12. Specifically, the exemption would permit use of an alternate methodology contained in WCAP-17444-P, Revision 0 (ADAMS Accession No. ML14216A406),
"Reactor Vessel Closure Head/Vessel Flange Requirements Evaluation for Seabrook Unit 1,"
October 2011. The exemption would permit the methodology contained in WCAP-17444-P, in lieu of the specific requirements of 1 O CFR Part 50, Appendix G, related to the establishment of minimum temperature criteria for all modes of reactor operation addressed by Table 1 of 1 O CFR Part 50, Appendix G, that are based on the properties of the material of the RPV closure flange region, that is highly stressed by the bolt preload for pressures greater than 20 percent of the pre-service hydrostatic test pressure. A non-proprietary version of WCAP-17 444-P is available in ADAMS under Accession No. ML14216A406. The requirements from which NextEra requested that Seabrook be exempted shall be referred to, for the purpose of this exemption, as those requirements related to the application of footnote (2) to Table 1 of 1 O CFR Part 50, Appendix G, for pressures greater than 20 percent of the pre-service hydrostatic test pressure. The licensee did not request exemption from those requirements related to the application of footnote (2) to Table 1 of 1 O CFR Part 50, Appendix G, for pressures less than or equal to 20 percent of the pre-service hydrostatic test pressure. These minimum temperature requirements (hereafter referred to as the minimum bolt-up temperature requirements) shall remain in effect for the Technical Specification (TS) P-T limit curves for all modes of reactor operation.
WCAP-17 444-P documents a linear elastic fracture mechanics (LEFM) analysis of postulated flaws in the Seabrook RPV closure flange region under normal operating conditions associated with RPV bolt-up, the 100 degrees Fahrenheit (°F) per hour reactor coolant system (RCS) heat-up transient, and the 100 °F per hour cool-down transient. The LEFM analysis was performed by first calculating through-wall stress distributions for the flange region based on a finite element analysis (FEA) for bolt-up and the 100 °F per hour heat-up and cool-down transients. The RCS heat-up and cool-down transients were evaluated by calculating the flange stresses as RCS pressure and temperature vary with time. The pressure and temperature changes were modeled based on realistic 100 °F per hour heat-up and cool-down transients that would be considered permissible for normal operating conditions based on the TS P-T limit curves. Therefore, the stress at any given temperature is based on a lower pressure than the limiting pressure from the proposed TS P-T limit curve, which is based on the limiting RPV beltline material properties and minimum bolt-up temperature requirement. The pressures used are those that are actually achievable based on physical properties of the reactor coolant during the heat-up process and the plant operating configuration, rather than what is permitted by the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code),
Section XI, Appendix G, P-T limits that are calculated based on the beltline material properties.
The NRG concluded in its safety evaluation (SE) (ADAMS Accession No. ML15205A333) that the licensee has demonstrated that the combination of high stresses along with low metal temperature in the RPV flange region cannot exist simultaneously, based on the NRG staff's evaluation of WCAP-17444-P and the licensee's RAI responses. The NRG staff determined that the licensee also demonstrated that the structural integrity of the Seabrook RPV closure flange materials will not be challenged by facility operation in accordance with the proposed TS P-T limit curves that are based on the Seabrook RPV beltline region and the flange minimum bolt-up temperature, without the minimum temperature requirements related to Footnote (2) to Table 1 of 10 CFR Part 50, Appendix G for pressures greater than 20 percent of the pre-service hydrostatic test pressure.
Therefore, for pressures greater than 20 percent of the pre-service hydrostatic test pressure, the minimum temperature requirements related to Footnote (2) to Table 1 of 1 O CFR Part 50, Appendix G are not necessary to meet the underlying intent of 1 O CFR Part 50, Appendix G, to protect the Seabrook RPV closure flange from brittle fracture during normal operation under both core critical and core non-critical conditions and RPV hydrostatic and leak test conditions.
Ill. Discussion.
Pursuant to 1 O CFR 50.12, the Commission may, upon application by any interested person or upon its own initiative, grant exemptions from the requirements of 1 O CFR Part 50 when: (1) the exemptions are authorized by law, will not present an undue risk to public health or safety, and are consistent with the common defense and security; and (2) when special circumstances are present. Under 1 O CFR 50.12(a)(2)(ii), special circumstances include, among other things, when application of the specific regulation in the particular circumstance would not serve, or is not necessary to achieve, the underlying purpose of the rule. The NRC staff's detailed review and technical basis for the approval of the exemption, requested by NextEra, is provided in the NRC staff's SE (ADAMS Accession No. ML15205A333).
A. The Exemption is Authorized by Law.
This exemption would allow the use of WCAP-17444-P, Revision 0, "Reactor Vessel Closure HeadNessel Flange Requirements Evaluation for Seabrook Unit 1," in lieu of the minimum temperature requirement that is based on the highest reference temperature of the material in the closure flange region that is highly stressed by the bolt preload, for pressures greater than 20 percent of the pre-service hydrostatic test pressure, as required by 1 O CFR 50, Appendix G, Table 1. As stated previously, 10 CFR 50.12(a)(2) allows the NRC to grant exemptions from the requirements of 1 O CFR Part 50, Appendix G, provided that special circumstances are present. As described below, the NRC staff has determined that special circumstances exist to grant the requested exemption. In addition, granting the exemption will not result in a violation of the Atomic Energy Act of 1954, as amended, or NRC regulations.
Therefore, the exemption is authorized by law.
B. The Exemption Presents No Undue Risk to Public Health and Safety.
The revised P-T limit curves developed for Seabrook reference the methodology described in WCAP-17 444-P, as the technical basis for eliminating the minimum temperature requirement for the flange for pressures greater than 20 percent of the pre-service hydrostatic test pressure. The WCAP-17 444-P methodology uses a higher material fracture toughness, K ie (fracture toughness based on the lower bound of static initiation critical values measured as a function of temperature) instead of K ia (fracture toughness based upon the lower bound of crack arrest critical values measured as a function of temperature), which results in less restrictive operating conditions for the flange than those required by Table 1 of 1 O CFR Part 50, Appendix G, for pressures greater than 20 percent of the pre-service hydrostatic test pressure. The regulations in 10 CFR 50, Appendix G, address the metal temperature of the closure head flange and vessel flange regions. The regulation states, in part, that the metal temperature of the closure flange regions must exceed the material un-irradiated nil-ductility reference temperature (RT NoT) by at least 120 °F for normal operation when the pressure exceeds 20 percent of the pre-service hydrostatic test pressure.
Implementing the P-T limit curves that use the Kie material fracture toughness without eliminating the flange requirement of 10 CFR 50, Appendix G, would place a restricted operating window in the temperature range associated with the flange/closure head (i.e., flange RTNoT + 120 °F). In accordance with WCAP-17444-P, the Kie toughness has been shown to provide significant margin between the applied stress intensity factor and the fracture toughness of the flange/closure head. Applying the WCAP-17444-P methodology for eliminating the flange minimum temperature requirement in the P-T limits, for pressures greater than 20 percent of the pre-service hydrostatic test pressure, will enhance overall plant safety by expanding the P-T operating window, especially in the region of low temperature operations.
The two primary safety benefits that would be realized are a reduction in the potential challenges to the cold overpressure mitigation system, and a reduction in the risk of damaging the reactor coolant pump seals. This will produce a significant improvement in plant safety by reducing the probability of an inadvertent reduction in reactor coolant inventory and in easing the burden on the operators. WCAP-17 444-P concludes that the integrity of the closure head/flange is not a concern for safe unit operation and testing. Therefore, the proposed exemption does not present an undue risk to the public health and safety.
C. The Exemption is Consistent with the Common Defense and Security.
The licensee requested an exemption to use WCAP-17 444-P in lieu of the minimum temperature requirement that is based on the highest reference temperature of the material in the closure flange region that is highly stressed by the bolt preload, for pressures greater than 20 percent of the pre-service hydrostatic test pressure, as required by 1 O CFR 50, Appendix G, Table 1. This exemption request is not related to, and does not impact, any security issues at Seabrook. Therefore, the NRC staff determined that this exemption does not impact, and is consistent with, the common defense and security.
D. Special Circumstances.
Special circumstances, in accordance with 10 CFR 50.12(a)(2)(ii), are present whenever application of the regulation in the particular circumstances is not necessary to achieve the underlying purpose of the rule. The underlying purpose of 1 O CFR 50.60 and 1 O CFR 50, Appendix G, is to protect the integrity of the reactor coolant pressure boundary. The regulations in 1 O CF~ 50, Appendix G, establish the requirements for the P-T limits for pressure retaining components of the reactor coolant pressure boundary and requirements for the minimum metal temperature of the RPV closure head flange and reactor vessel flange regions. The P-T limits are determined using the methodology of the ASME Code,Section XI, Appendix G, with additional, more restrictive, flange temperature requirements specified in 10 CFR 50, Appendix G.
The NRC staff examined the licensee's rationale to support the exemption request.
Based on its consideration of the information provided in WCAP-17 444-P and the information provided in the licensee's letters dated April 24 and June 24, 2015, an acceptable technical basis has been established to exempt Seabrook from the requirements related to Footnote 2 to Table 1 of 1 O CFR Part 50, Appendix G, for RCS pressures greater than 20 percent of the pre-service hydrostatic test pressure. The technical basis provided by the licensee has established that an adequate margin of safety against brittle failure would continue to be maintained for the Seabrook RPV without the application of those requirements related to Footnote 2 to Table 1 of 1 O CFR Part 50, Appendix G, for normal operation under both core critical and core non-critical conditions and RPV hydrostatic and leak test conditions, for RCS pressures greater than 20 percent of the pre-service hydrostatic test pressure.
Therefore, the special circumstances required by 10 CFR 50.12(a)(2)(ii) for the granting of an exemption exist.
E. Environmental Considerations.
The NRC staff determined that the exemption discussed herein meets the eligibility criteria for the categorical exclusion set forth in 1 O CFR 51.22(c)(9), because it is related to a requirement concerning the installation or use of a facility component located within the restricted area, as defined in 1 O CFR Part 20, and issuance of this exemption involves (i) no significant hazards consideration, (ii) no significant change in the types or a significant increase in the amounts of any effluents that may be released offsite, and (iii) no significant increase in individual or cumulative occupational radiation exposure. Therefore, in accordance with 10 CFR 51.22(b), no environmental impact statement or environmental assessment need to be prepared in connection with the NRC staff's consideration of this exemption request. The basis for the NRC staff's determination is discussed as follows, with an evaluation against each of the requirements in 10 CFR 51.22(c)(9)(i) - (iii).
Requirements in 1 O CFR 51.22(c)(9)(i)
The NRC staff evaluated whether the exemption involves no significant hazards consideration using the standards described in 1 O CFR 50.92(c), as presented below:
- 1. Does the proposed exemption involve a significant increase in the probability or consequences of an accident previously evaluated?
Response: No.
The proposed exemption does not impact the physical function of plant structures, systems, or components (SSCs) or the manner in which SSCs perform their design function.
Operation in accordance with the proposed WCAP-17 444 will ensure that all analyzed accidents will continue to be mitigated by the SSCs as previously analyzed. The proposed exemption does not alter or prevent the ability of operable SSCs to perform their intended function to mitigate the consequences of an initiating event within assumed acceptance limits. The proposed exemption neither adversely affects accident initiators or precursors, nor alter design assumptions.
Therefore, this exemption does not involve a significant increase in the probability or consequences of an accident previously evaluated.
- 2. Does the proposed exemption create the possibility of a new or different kind of accident from any accident previously evaluated?
Response: No.
The proposed exemption does not involve a physical alteration of the plant (i.e., no new or different type of equipment will be installed), does not create new failure modes for existing equipment, or create any new limiting single failures. The exemption will continue to ensure that appropriate fracture toughness margins are maintained to protect against reactor vessel failure, during both normal and low temperature operation. The proposed exemption is consistent with the applicable NRC approved methodologies (i.e., WCAP-17444-P, Revision 0). Plant operation will not be altered, and all safety functions will continue to perform as previously assumed in accident analyses.
Therefore, this exemption does not create the possibility of a new or different kind of accident from an accident previously evaluated.
- 3. Does the proposed exemption involve a significant reduction in a margin of safety?
Response: No.
Margin of safety is associated with confidence in the ability of the fission product barriers (i.e., fuel cladding, reactor coolant system pressure boundary, and containment structure) to limit the level of radiation dose to the public. The proposed exemption will not adversely affect the operation of plant equipment or the function of any equipment assumed in the accident analysis. The proposed exemption was developed using NRC-approved methodologies and will continue to ensure an acceptable margin of safety is maintained. The safety analysis acceptance criteria are not affected by this exemption. The proposed exemption will not result in plant operation in a configuration outside the design basis. The proposed exemption does not adversely affect systems that respond to safely shut down the plant and to maintain the plant in a safe shutdown condition.
Therefore, this exemption does not involve a significant reduction in a margin of safety.
Based on the above evaluation of the standards set forth in 10 CFR 50.92(c), the NRC staff concludes that the proposed exemption involves no significant hazards consideration.
Accordingly, the requirements of 10 CFR 51.22(c)(9)(i) are met.
Requirements in 10 CFR 51.22(c)(9)(ii)
The proposed exemption would allow the use of WCAP-17444-P, Revision 0, in lieu of the highest reference temperature of the material in the closure flange region that is highly stressed by the bolt preload required by 10 CFR 50, Appendix G, Table 1. WCAP-17444 demonstrates that the flange region can tolerate assumed flaws of 0.1 T (thickness) during the heat-up, cool-down, and bolt-up conditions. Additionally, it can be concluded that flaws are unlikely to initiate in the flange region, since there is no known degradation mechanism for the flange region and the fatigue usage in the flange region is less than 0.1 T. Furthermore, based on WCAP-17 444, the alternative flange temperature requirement of 46 °F is less than the minimum bolt-up temperature of 60 °F for Seabrook. Therefore, the proposed exemption will not significantly change the types of effluents that may be released offsite, or significantly increase the amount of effluents that may be released offsite. Therefore, the requirements of 10 CFR 51.22(c)(9)(ii) are met.
Requirements in 1 O CFR 51.22(c)(9)(iii)
The proposed exemption would allow the use of WCAP-17444-P, Revision 0, in lieu of the methodology required by 1 O CFR 50, Appendix G, Footnote (2), to Table 1. Therefore, the proposed exemption will not significantly increase individual occupational radiation exposure or significantly increase cumulative occupational radiation exposure. Therefore, the requirements of 10 CFR 51.22(c)(9)(iii) are met.
Conclusion Based on the above, the NRC staff concludes that the proposed exemption meets the eligibility criteria for the categorical exclusion set forth in 1 O CFR 51.22(c)(9). Therefore, in accordance with 1 O CFR 51.22(b ), no environmental impact statement or environmental assessment need be prepared in connection with the NRC's issuance of this exemption.
IV. Conclusions.
Accordingly, the Commission has determined that pursuant to 10 CFR 50.12(a), the exemption is authorized by law, will not present an undue risk to the public health and safety, and is consistent with the common defense and security. Also, special circumstances are present. Therefore, the Commission hereby grants the licensee an exemption from 1 O CFR 50.60 to permit the use of WCAP-17 444-P in lieu of the highest reference temperature of the material in the closure flange region that is highly stressed by the bolt preload required by 1 O CFR 50, Appendix G, Table 1 for Seabrook. This exemption is effective upon issuance.
Dated at Rockville, Maryland, this 28th day of July 2015.
For the Nuclear Regulatory Commission.
George Wilson, Acting Director, Division of Operating Reactor Licensing, Office of Nuclear Reactor Regulation.
ENCLOSURE 2 SAFETY EVALUATION RELATED TO NEXTERA ENERGY SEABROOK, LLC SEABROOK STATION, UNIT 1 DOCKET NO. 50-443 REQUEST FOR EXEMPTION FROM TABLE 1 OF 10 CFR PART 50, APPENDIX G
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO REQUEST FOR EXEMPTION FROM TABLE 1 OF
1.0 INTRODUCTION
10 CFR PART 50, APPENDIX G NEXTERA ENERGYSEABROOK. LLC SEABROOK STATION, UNIT 1 DOCKET NO. 50-443 By letter dated July 24, 2014 (Agencywide Documents Access and Management System (ADAMS) Accession Number ML14216A403), as supplemented by letters dated March 9, April 24, and June 24, 2015 (ADAMS Accession Nos. ML15072A023, ML15125A140, and ML15181A262), NextEra Energy Seabrook, LLC (NextEra or the licensee) submitted a request for an exemption from Title 10 of the Code of Federal Regulations (10 CFR), Section 60 for Seabrook Station, Unit 1 (Seabrook).
The exemption would permit the use of the of the provisions of WCAP-17444-P, "Reactor Vessel Closure HeadNessel Flange Requirements Evaluation for Seabrook Unit 1,
October 2011, in lieu of the minimum temperature requirements of 1 O CFR Part 50, Appendix G that are based on the material properties of the reactor pressure vessel (RPV) closure flange region, for pressures greater than 20 percent of the pre-service hydrostatic test pressure.
The licensee requested the exemption to implement the provisions of a license amendment request (LAR), also submitted in its letter dated July 24, 2014, to revise the pressure-temperature (P-T) limit curves established in the Seabrook Technical Specifications (TSs).
To support the U.S. Nuclear Regulatory Commission (NRC) staff's technical basis for the exemption, NextEra submitted a letter dated July 9, 2015 (ADAMS Accession No. ML15194A042), that revised the proposed TS P-T limit curves to restrict the reactor coolant heat-up rate at temperatures less than 120 °F.
2.0 REGULATORY EVALUATION
The regulations in 10 CFR 50.12(a)(2)(ii) provide that the NRC may, upon application by a licensee or on its own initiative, grant exemptions from the requirements of the regulations in circumstances in which application of the regulation would not serve the underlying purpose of the rule or is not necessary to achieve the underlying purpose of the rule 1.
10 CFR Part 50, Appendix G, "Fracture Toughness Requirements," states in part:
This appendix specifies fracture toughness requirements for ferritic materials of pressure-retaining components of the reactor coolant pressure boundary of light water nuclear power reactors to provide adequate margins of safety during any condition of normal operation, including anticipated operational occurrences and system hydrostatic tests, to which the pressure boundary may be subjected over its service lifetime.
General Design Criterion 31, "Fracture prevention of reactor coolant pressure boundary,"
requires that the reactor coolant pressure boundary be designed with sufficient margin to assure that when stressed under operating, maintenance, testing, and postulated accident conditions (1) the boundary behaves in a non-brittle manner and (2) the probability of rapidly propagating fracture is minimized. The design shall reflect consideration of service temperatures and other conditions of the boundary material under operating, maintenance, testing, and postulated accident conditions and the uncertainties in determining (1) material properties, (2) the effects of irradiation on material properties, (3) residual, steady state and transient stresses, and (4) size of flaws.
10 CFR 50.60 "Acceptance criteria for fracture prevention measures for lightwater nuclear power reactors for normal operation," which states:
(a) Except as provided in paragraph (b) of this section, all light-water nuclear power reactors, other than reactor facilities for which the certifications required under §50.82(a)(1) have been submitted, must meet the fracture toughness and material surveillance program requirements for the reactor coolant pressure boundary set forth in appendices G and H to this part.
(b) Proposed alternatives to the described requirements in Appendices G and H of this part or portions thereof may be used when an exemption is granted by the Commission under§ 50.12.
3.0 TECHNICAL EVALUATION
1 O CFR Part 50, Appendix G, "Fracture Toughness Requirements," requires that P-T limits and minimum temperature criteria be established for RPVs during normal operating and hydrostatic or leak rate testing conditions. Regarding minimum temperature requirements, 10 CFR Part 50, Appendix G states the following:
1 Notwithstanding the special circumstances of the exemption request, 10 CFR 50.12(a)(1) requires that the exemption must be authorized by law, not present an undue risk to the public health and safety, and be consistent with the common defense and security.
The minimum temperature requirements... pertain to the controlling material, which is either the material in the closure flange or the material in the beltline region with the highest reference temperature.... the minimum temperature requirements and the controlling material depend on the operating condition (i.e.,
hydrostatic pressure and leak tests, or normal operation including anticipated normal operational occurrences), the vessel pressure, whether fuel is in the vessel, and whether the core is critical. The metal temperature of the controlling material, in the region of the controlling material which has the least favorable combination of stress and temperature, must exceed the appropriate minimum temperature requirement for the condition and pressure of the vessel specified in Table 1 [of 1 O CFR Part 50, Appendix G].
Additionally, Footnote 2 to Table 1 in 1 O CFR Part 50, Appendix G specifies that RPV minimum temperature requirements related to RPV closure flange considerations shall be based on "[t]he highest reference temperature of the material in the closure flange region that is highly stressed by bolt preload."
Pursuant to 10 CFR 50.12, by letter dated July 24, 2014, as supplemented by letters dated March 9, April 24, and June 24, 2015, NextEra requested an exemption from 1 O CFR 50.60, "Acceptance criteria for fracture prevention measures for light water nuclear power reactors for normal operation." The exemption would permit the use of the provisions of the Westinghouse report, WCAP-17444-P, Rev. 0, "Reactor Vessel Closure HeadNessel Flange Requirements Evaluation for Seabrook Unit 1," October 2011, in lieu of the specific requirements of 1 O CFR Part 50, Appendix G, related to the establishment of minimum temperature criteria for all modes of reactor operation addressed by Table 1 of 10 CFR Part 50, Appendix G. These minimum temperature criteria are based on the properties of the material of the RPV closure flange region that is highly stressed by the bolt preload, for pressures greater than 20 percent of the pre-service hydrostatic test pressure. The non-proprietary version of WCAP-17 444-P (WCAP-17 444-NP) is available for public examination under ADAMS Accession No. ML14216A406.
The licensee requested the exemption in order to implement the provisions of a LAR to revise the P-T limit curves established in the Seabrook TSs.
The requirements from which the licensee requested that Seabrook be exempted shall be referred to, for the purpose of this exemption, as those requirements related to the application of Footnote 2 to Table 1 of 1 O CFR Part 50, Appendix G for pressures greater than 20 percent of the pre-service hydrostatic test pressure. NextEra did not request exemption from those requirements related to the application of Footnote 2 to Table 1 of 10 CFR Part 50, Appendix G for pressures less than or equal to 20 percent of the pre-service hydrostatic test pressure.
These minimum temperature requirements (hereafter referred to as the minimum bolt-up temperature requirements) shall remain in effect for the proposed TS P-T limit curves for all modes of reactor operation.
WCAP-17444-P documents a linear elastic fracture mechanics (LEFM) analysis of postulated flaws in the Seabrook RPV closure flange region under normal operating conditions associated with RPV bolt-up, the 100 °F per hour reactor coolant system (RCS) heat-up transient, and the 100 °F per hour cool-down transient. The LEFM analysis was performed by first calculating through-wall stress distributions for the flange region based on a finite element analysis (FEA) for bolt-up and the 100 °F per hour heat-up and cool-down transients. The RCS heat-up and cool-down transients were evaluated by calculating the flange stresses as RCS pressure and temperature vary with time. The P-T changes were modeled based on realistic 100 °F per hour heat-up and cool-down transients that would be considered permissible for normal operating conditions based on the proposed TS P-T limit curves. Therefore, the stress at any given temperature is based on a lower pressure than the limiting pressure from the proposed TS P-T limit curve, which is based on the limiting RPV beltline material properties and minimum bolt-up temperature requirement. The pressures used are those that are actually achievable based on physical properties of the reactor coolant during the heat-up process and the plant operating configuration, rather than what is permitted by the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code),Section XI, Appendix G P-T limits that are calculated based on the beltline material properties. However, as discussed below in its evaluation of the licensee's RAI responses, the NRG staff was able to verify that there is adequate assurance that flange integrity would be maintained with the required safety margin even for P-T in accordance with the proposed TS P-T limit curves. Therefore, the NRG staff finds the use of the realistic transient P-T to be acceptable.
WCAP-17 444-P indicates that the highest stresses were found to occur at two limiting locations:
(1) the top head torus-to-flange weld at the bolt-up condition, and (2) the top head dome-to-torus weld at the end of the 100 °F per hour heat-up transient. With these stresses, Westinghouse calculated the applied stress intensity factor (K1) for postulated semi-elliptical outside diameter (OD) surface breaking flaws with an aspect ratio (length vs. depth) of 6:1, and with depths ranging from 0 to 80 percent of the thickness of the component low alloy steel pressure boundary. The K1 values were calculated by using stress intensity factor influence coefficients that were derived from a polynomial fit to the through-wall stress distributions from the FEA. This methodology for calculating K1 is consistent with the ASME Code Section XI,
Appendix G, Paragraph G-2220 requirements for the analysis of structural discontinuity locations. WCAP-17 444-P compared the K1 values for the OD flaw with depth equal to one-tenth of the flange pressure boundary thickness (0.1 t) to the lower bound plane strain fracture toughness values for static crack initiation (Kie). The Kie values were calculated in accordance with the ASME Code,Section XI, Appendix G, Paragraph G-2110 based on the most limiting nil-ductility transition reference temperature (RT NoT) value for the Seabrook RPV closure flange materials.
The use of Kie as the fracture toughness property represents the most significant difference between the LEFM analysis provided in WCAP-17 444-P and the analysis that was performed as the basis for establishing the minimum temperature requirements in Table 1 of 10 CFR Part 50, Appendix G. The minimum temperature requirements related to Footnote (2) to Table 1 of 10 CFR Part 50, Appendix G were incorporated into 10 CFR based on the evaluation documented in the 1983 Commission Rulemaking Issue Paper ("SECY Paper"), SECY-83-80, "1 O CFR Part 50 - General Revision of Appendices G and H, Fracture Toughness and Reactor Vessel Material Surveillance Requirements," February 25, 1983. These minimum temperature requirements are based on analyses that used the ASME Code lower bound crack arrest fracture toughness (K1A) as the parameter for characterizing a material's ability to resist crack initiation. The use of K1A is more conservative than Kie for LEFM evaluations, and its use in the SECY-83-80 evaluation that established the minimum temperature requirements in 10 CFR Part 50, Appendix G was based on the limited knowledge of RPV material behavior that was available at that time. It has since been established that the use of Kie, not K1A, is consistent with the actual physical processes that would govern crack initiation under conditions of normal RPV operation, including RPV heat-up, cool-down, and hydrostatic and leak testing. Based on this understanding of the behavior of RPV materials, Kie was incorporated into the ASME Code,Section XI, Appendix Gin the 1990s. Accordingly, the RPV beltline P-T limit curves are now routinely calculated using Kie as the fracture toughness property, which is in accordance with the 1 O CFR Part 50, Appendix G requirement that the P-T limits must be at least as conservative as those obtained based on the methods of analysis in the ASME Code,Section XI, Appendix G.
Table 6-2 of WCAP-17444-P demonstrates that the ASME Code-required margin against fracture, as quantified by the ratio of Kie to K1 (K1dK1), is maintained for the limiting flange locations for the bolt-up condition and for the end of heat-up. Specifically K1dK1 is equal to 2.31 for the top head torus-to-flange weld for the bolt-up condition, and 3.73 for the top head dome-to-torus weld at the end of heat-up, based on the 0.1 t postulated flaw. Therefore, in both cases, the margin against fracture exceeds the requirements of the ASME Code,Section XI, Appendix G, which specifies a margin of two on K1 components due to primary stresses (i.e.
stresses caused by pressure loading and bolt preload) and a margin of one on K1 components due to secondary stresses, which include thermal transient stresses (i.e., through-wall thermal stresses caused by the normal heat-up and cool-down transients). The bolt-up condition corresponds to the condition of low metal temperature (and correspondingly low fracture toughness) in the flange region and relatively low stress, whereas the end of heat-up represents a condition of high metal temperature (and correspondingly high fracture toughness) and the highest stress. The more limiting of the two cases is the bolt-up condition due to the much lower fracture toughness compared to the end of heat-up.
With respect to the use of the 0.1 t OD postulated flaw for determining the above margins against fracture, the NRC staff found that this flaw depth is justified, in part, because the evaluation documented in SECY-83-80 (the technical basis for the current minimum temperature requirements related to Footnote (2) to Table 1 of 1 O CFR Part 50, Appendix G) was based on the same flaw parameters, including the 0.1t flaw depth, for the flange region. In addition, WCAP-17 444-P indicates that the use of the 0.1 t reference flaw depth for the K1 calculations is based on established industry flaw detection capability for flaws in RPVs.
Appendix A to WCAP-17444-P provides an industry proprietary evaluation of RPV inservice inspection reliability, which demonstrates that 0.1 t is still the appropriate reference flaw depth for an OD surface breaking flaw in the flange region. Additionally, the ASME Code,Section XI,
Appendix G states that, "[s]maller [postulated] defect sizes [relative to the 1/4t flaw normally postulated for the beltline region] may be used on an individual case basis if a smaller size of maximum postulated defect can be ensured." Therefore, for reasons discussed above, the NRC staff determined that the 0.1t flaw depth is acceptable for the flange region.
WCAP-17 444-P also provided justification for the location of the 0.1 t postulated flaw at the OD of the RPV flange region. This justification indicates that the primary bending stress for the bolt-up condition results in tensile stress at the OD and compressive stress at the inside diameter (ID). In addition, the heat-up transient also results in tensile thermal stress at the OD and compressive thermal stress at the ID, whereas the cool-down transient results in compressive stress at the OD and tensile stress at the ID (i.e., the through-wall thermal stress resulting from cool-down counteracts the bolt-up stress). Membrane stress due to internal pressure during heat-up and cool-down is tensile at all locations. Therefore, the maximum tensile stress is produced at the OD during the heat-up transient. The NRC staff determined that these stress profiles are consistent with the loads associated with bolt-up and through-wall temperature gradients for the RPV closure head flange geometry and noted that the stress distribution outputs from the fEA of the flange confirm this description of the stress profile. Therefore, the NRC staff found that the use of the 0.1t postulated flaw at the OD of the RPV flange region is acceptable for demonstrating adequate margins against fracture for the flange region.
Discussion of Staff RA/ and Licensee RA/ Responses Based on its review of WCAP-17444-P, the NRC staff determined that additional information was required in order resolve several concerns associated with the limiting flange RT NOT value, the 100 °f per hour heat-up rate, the flange through-wall stress distributions, and the LEfM results for low temperature operations. The NRC staff's RAI and the licensee's RAI response, dated April 23, 2015 (ADAMS Accession No. ML15125A140) are discussed below.
The NRC staff noted that WCAP-17444-P lists RTNoT values for the Seabrook closure head and flange components. The most limiting of these values was selected for determining Kie. In RAl-1, the NRC staff requested that the licensee confirm whether the RT NOT values for the base metal components of the closure flange region are measured heat-specific values from certified material test reports that were determined in accordance with the ASME Code, Section Ill, NB-2331 requirements.
In its response to RAl-1, NextEra stated that the RT NOT values for the base metal components of the closure flange region are measured heat-specific values from certified material test reports.
The licensee indicated that the Seabrook RPV was designed in accordance with the 1971 Edition through Winter 1972 Addenda of the ASME Code, Section Ill, NB-2300, which required testing of RPV base metal specimens in the transverse (i.e., weak direction). The NRC staff noted that this Code Addenda includes the provisions of NB-2331 for establishing RT NoT.
Therefore, the NRC staff found that these RT NOT values are an acceptable material property.
basis for the flange LEfM analysis. Accordingly, RAl-1 is resolved.
In reviewing WCAP-17444-P stress analysis results, the NRC staff noted a discrepancy between the axial stress distribution for the end of the 100 °f per hour heat-up transient provided in WCAP-17444-P Table 6-1 and the axial stress distribution for the corresponding condition in Appendix C of WCAP-17444-P. Therefore, in RAl-2, the NRC staff requested that the licensee address this discrepancy.
In its response to RAl-2, NextEra stated that the difference between the stress values reported in WCAP-17444-P, Table 6-1 and Appendix C is due to the inclusion of weld residual stresses in the stress values reported in WCAP-17444-P Table 6-1. The licensee stated that the Appendix C stress distributions are from the fEA and do not include the residual stress. The NRC staff noted that Section 6 of WCAP-17444-P also states the through-wall welding residual profile was added to the bolt-up and to the heat-up and cool-down transient pressure and thermal stresses. Since WCAP-17444-P Table 6-1 stress values were used to calculate the K1 values for demonstrating adequate margins against fracture, and the addition of weld residual stress represents an additional conservatism in the analysis, the NRC staff found the incorporation of these stresses in Table 6-1 acceptable. Therefore, RAl-2 is resolved.
The NRC staff performed a calculation to verify the bounding RCS heat-up rate described in WCAP-17 444-P and noted that the heat-up and pressurization of the RCS from the minimum bolt-up temperature to the temperature specified in WCAP-17444-P Table 6-1 tor the end of heat-up, within the time specified for the end of heat-up, resulted in a heat-up rate of approximately 87 °F per hour. Therefore, the NRC staff requested in RAl-3 that the licensee address how WCAP-17444-P flange integrity analysis is applicable to a 100 °F per hour heat-up rate.
In its response to RAl-3, NextEra stated that, for the LEFM evaluation, the 100 °F per hour heat-up transient starts at an RCS temperature of 120 °F and a time of 82 minutes, and ends at a temperature of 557 °F and a time 344.2 minutes, corresponding to a 100 °F per hour heat-up rate. The licensee indicated that this represents standard design plant heat-up conditions. The licensee cited the Seabrook Updated Final Safety Analysis Report (UFSAR), Section 3.9(N) as the basis tor this heat-up transient.
The NRC staff verified that the heat-up of the RCS from 120 °F to 557 °F, over the time interval from 82 minutes to 344.2 minutes, corresponds to a 100 °F per hour heat-up rate. The NRC staff also verified that the Seabrook UFSAR Section 3.9(N) states the following:
The design heat-up and cool-down cases are conservatively represented by continuous operations performed at a uniform temperature rate of 100 °F per hour... For these cases, the heat-up occurs from ambient (assumed to be 120 °F) to the no-load temperature and pressure condition and the cool-down represents the reverse situation.
Therefore, the NRC staff found that the licensee adequately demonstrated that WCAP-17 444-P LEFM analysis considered a 100 °F per hour heat-up rate. Thus RAl-3 is resolved.
The NRC staff performed an independent calculation, which showed that at a metal temperature of 94 °F, the Kie for the flange exceeds twice the maximum value tor the applied K1 at the end of heat-up. The end of heat-up corresponds to the condition of the highest stress in the flange.
Therefore, the ASME Code-required margins against fracture would be ensured for RCS operation in accordance with the proposed TS P-T limit curves if the flange metal temperature is greater than or equal to 94 °F. For flange metal temperatures less than 94 °F, the ASME Code-required margins against fracture would be maintained provided that the K1 tor the flange does not increase drastically early in the heat-up transient before the flange metal has reached a temperature and fracture toughness necessary for ensuring sufficient margins against fracture.
Therefore, the NRC staff was concerned that the increase in the applied K1 values early in the heat-up transient due to a combination of bolt-up stress plus pressure and thermal stresses, while the Kie fracture toughness is still relatively low, would result in a more limiting ratio of Kie to K1 that could possibly not meet the ASME Code-required margin against fracture. Therefore, for the 100 °F per hour heat-up transient, the NRC staff requested in RAl-4 that the licensee address whether the most limiting ratio of Kie to K1 occurs at bolt-up. If the most limiting ratio of Kie to K1 does not occur at bolt-up, the NRC staff requested that the licensee provide the most limiting ratio, the corresponding time during the heat-up transient, and the values of K1 and Kie at that time.
In its response to RAl-4, NextEra provided the most limiting ratio of Kie to K1 at the time corresponding to the beginning of the 100 °F per hour heat-up transient with the flange metal temperature set equal to 60 °F. This calculation was provided in order to demonstrate that adequate margins against fracture would be maintained if the higher stress in the flange corresponding to the beginning of the heat-up transient occurred while the flange was at the minimum bolt-up temperature of 60 °F. The NRC staff reviewed the calculation and determined that it demonstrates that the ASME Code,Section XI, Appendix G-required margins against fracture would still be maintained at the start of the 100 °F per hour heat-up even if the flange metal temperature were still at the minimum bolt-up temperature. The NRC staff confirmed that this calculation is based on the most bounding assumptions with respect to flange metal temperature and applied stress for the beginning of RCS heat-up - specifically, Kie is based on the lowest temperature for the flange material (60 °F), and the applied K1 value is based on the elevated stress in the flange at the start of heat-up. Accordingly, the calculation serves to demonstrate that the ASME Code-required margins against fracture for the flange region would not be violated for Seabrook for bounding conditions associated with the unfavorable combination of low metal temperature and elevated stress in the flange. Therefore, the NRC staff found that the flange integrity would be maintained with the required safety margin for the start of the heat-up transient and at the lowest allowable flange temperature permitted on the proposed TS P-T limit curves, thereby providing assurance that the minimum temperature requirements related to Footnote (2), for pressures greater than 20 percent of the pre-service hydrostatic test pressure, are not necessary to meet the underlying intent of 1 O CFR Part 50, Appendix G.
In its response to RAl-4, NextEra also provided a description of the design transient for heat-up.
The licensee stated that the design heat-up transient, as specified in the Seabrook UFSAR Section 3.9(N), starts at 120 °F and ramps up to 557 °F at a rate of 100 °F per hour. The licensee indicated that this design transient is used in WCAP-17444-P evaluation. The licensee explained that below 120 °F, the RCS is depressurized and at a uniform temperature. The licensee noted that RCS temperature changes between 70 °F and 120 °F are very slow and do not cause significant thermal transient effects in the closure flange region. The licensee stated that this is consistent with TS requirements, where TS Table 1.2 defines Mode 5, "Cold Shutdown, as 200 °F or below with the RPV head tensioned. The licensee also stated that evolutions in Mode 5 such as RCS evacuation and fill or pressurizer bubble formation do not produce rapid temperature changes below 120 °F.
To illustrate the essentially isothermal conditions at low temperatures, the licensee described the most recent plant startup after the March 2014 refueling outage, where the initial heat-up from ambient conditions occurred from 88.5 °F to 155.7 °F over 11 hours1.273148e-4 days <br />0.00306 hours <br />1.818783e-5 weeks <br />4.1855e-6 months <br />, corresponding to a heat-up rate of approximately 6.1 °F per hour. Based on these limitations, the licensee emphasized that for temperatures less than 120 °F there are no significant thermal transient stresses that should be considered for WCAP-17 444-P LEFM evaluation.
Based on its review of UFSAR Section 3.9(N) and the licensee's response to RAl-4, the NRC staff found that the licensee adequately demonstrated that the 100 °F per hour heat-up rate does not start at RCS temperatures less than 120 °F. The NRC staff also determined that maintaining the RCS heat-up rate less than or equal to 20 °F per hour for RCS temperatures less than 120 °F would ensure that conditions in the RPV flange region are adequately close to isothermal, such that the ASME Code-required margins against fracture are maintained for the RPV flange region for RCS operation in accordance with the proposed TS P-T limits. In order to ensure consistency between the design-basis conditions for the start of the 100 °F per hour heat-up transient and the proposed TS P-T limit curves, the NRC staff requested that the licensee notate the proposed TS P-T limit curve for heat-up with the requirement that the RCS heat-up rate be maintained less than or equal to 20 °F per hour for RCS temperatures less than 120 °F. In its response to RAl-5, provided by letter dated July 9, 2015 (ADAMS Accession No. ML15194A042), the licensee included this notation in the proposed TS P-T limit curve for heat-up. Therefore, since the NRC staff determined that the necessary margins against fracture are ensured for RCS operation in accordance with the proposed TS P-T limit curves for flange metal temperatures greater than 94 °F, the lowest allowable temperature of 120 °F for the start of the 100 °F per hour heat-up transient would also ensure that the flange metal temperature and fracture toughness are high enough for maintaining the ASME Code-required margins against fracture for RCS operation in accordance with the proposed TS P-T limit curves. Accordingly, the NRC staff determined that RAl-4 is resolved.
Based on its evaluation of WCAP-17444-P and the licensee's RAI response, the NRC staff determined that the licensee has demonstrated that the combination high stresses along with low metal temperature in the RPV flange region cannot exist simultaneously. The NRC staff determined that the licensee also demonstrated that the structural integrity of the Seabrook RPV closure flange materials will not be challenged by facility operation in accordance with the proposed TS P-T limit curves that are based on the Seabrook RPV beltline region and the flange minimum bolt-up temperature, without the minimum temperature requirements related to Footnote (2) to Table 1 of 10 CFR Part 50, Appendix G for pressures greater than 20 percent of the pre-service hydrostatic test pressure.
Therefore, for pressures greater than 20 percent of the pre-service hydrostatic test pressure, the minimum temperature requirements related to Footnote (2) to Table 1 of 10 CFR Part 50, Appendix G are not necessary to meet the underlying intent of 1 O CFR Part 50, Appendix G, to protect the Seabrook RPV closure flange from brittle fracture during normal operation under both core critical and core non-critical conditions and RPV hydrostatic and leak test conditions.
4.0 EXEMPTION Pursuant to 1 O CFR 50.12, the Commission may, upon application by any interested person or upon its own initiative, grant exemptions from the requirements of 10 CFR Part 50 when: (1) the exemptions are authorized by law, will not present an undue risk to public health or safety, and are consistent with the common defense and security; and (2) when special circumstances are present. Evaluation of the exemption criteria (1) above for each of the following exemption is addressed in the NRC exemption, Sections Ill.A, 111.B, and 111.C of Enclosure 1 to this letter. The evaluation of the special circumstances provision in (2) above is evaluated in Sections 4.1 of this SE.
Special circumstances exist when application of the regulation in the particular circumstance would not serve the underlying purpose of the rule or.is not necessary to achieve the underlying purpose of the rule (1 O CFR 50.12(a)(2)(ii)).
4.1 Specific Exemption for Table 1 of 1 O CFR 50, Appendix G The underlying purpose of Footnote (2) to Table 1 of 1 O CFR Part 50, Appendix G is to protect the integrity of the RPV flange portion of the reactor coolant pressure boundary during normal operations, including heat-up, cool-down, and during hydrostatic pressure and leak tests. The NRC staff accepts the licensee's determination that an exemption would be required to permit NextEra to not meet those requirements specifically related to the application of Footnote (2) to Table 1 of 1 O CFR Part 50, Appendix G for RCS pressures greater than 20 percent of the pre-service hydrostatic test pressure.
The NRC staff examined the licensee's rationale to support the exemption request. Based on its consideration of the information provided in WCAP-17 444-P and the RAI response provided in the licensee's letters dated March 9, April 24, and July 9, 2015, an acceptable technical basis has been established to exempt Seabrook from the requirements related to Footnote (2) to Table 1 of 10 CFR Part 50, Appendix G for RCS pressures greater than 20 percent of the pre-service hydrostatic test pressure. The technical basis provided by the licensee has established that an adequate margin of safety against brittle failure would continue to be maintained for the Seabrook RPV without the application of those requirements related to Footnote (2) to Table 1 of 10 CFR Part 50, Appendix G, for normal operation under both core critical and core non-critical conditions and RPV hydrostatic and leak test conditions, for RCS pressures greater than 20 percent of the pre-service hydrostatic test pressure. Therefore, the NRC staff concludes that, pursuant to 10 CFR 50.12(a)(2)(ii), special circumstances are present because the underlying purpose of 1 O CFR Part 50, Appendix G will be achieved without the application of those minimum temperature requirements that specifically relate to Footnote (2) to Table 1 of 10 CFR Part 50, Appendix G for RCS pressures greater than 20 percent of the pre-service hydrostatic test pressure, and therefore, the proposed exemption should be granted to the licensee such that those requirements related to the application of Footnote (2) to Table 1 of 10 CFR Part 50, Appendix G, for RCS pressures greater than 20 percent of the pre-service hydrostatic test pressure, need not be applied to Seabrook.
5.0 ENVIRONMENTAL CONSIDERATION
The environmental considerations for the exemption request are addressed in Section 111.E of the associated exemption (ADAMS Accession No. ML15092A519).
6.0 CONCLUSION
The NRC staff has completed its review of the licensee's request for an exemption from Table 1 of Appendix G to 10 CFR Part 50, as specified in this safety evaluation. The requirements of Appendix G to 1 O CFR Part 50 that remain in effect are provided in the licensee's letter dated July 24, 2014, as supplemented by letters dated March 9, April 24, and June 24, 2015. On the basis of its review, the NRC staff concludes that an adequate margin of safety against brittle failure would continue to be maintained for the Seabrook RPV without the application of those requirements related to Footnote (2) to Table 1 of 10 CFR Part 50, Appendix G, for normal operation under both core critical and core non-critical conditions and RPV hydrostatic and leak test conditions, for RCS pressures greater than 20 percent of the pre-service hydrostatic test pressure.
Accordingly, the NRC staff has determined that, pursuant to 1 O CFR 50.12(a), the exemption evaluated above is authorized by law, will not present an undue risk to the public health and safety, and are consistent with the common defense and security. Also, special circumstances are present. Specifically, the NRC staff finds the licensee's requested exemption meets the underlying purpose of the requirements in Appendix G to 10 CFR Part 50, and acceptably satisfies the special circumstances in 10 CFR 50.12(a)(2)(ii).
The Seabrook license amendment request that incorporates this exemption will be reviewed separately under the 10 CFR 50.90 license amendment process.
Principal Contributor: C. Sydnor, NRR Date: July 28, 2015
Package: ML15205A334 L TR ML15096A143 Exemption FRN: ML15092A519 SE* ML15205A333
- via memo OFFICE DORULPL 1-2/PM DORULPL 1-2/LA OGC DE/EVIB/BC*
NAME JLamb LRonewicz BMizuno JMcHale DATE 7/8/2015 7/8/2015 7/9/2015 6/25/2015 OFFICE DORULPL 1-2/BC DORUD(A)
DORULPL 1-2/PM NAME REnnis for DBroaddus ALLund JLamb DATE 7/27/2015 7/28/2015 7/28 /2015