80 FR 46066 - NextEra Energy Seabrook, LLC, Seabrook Station, Unit 1

NUCLEAR REGULATORY COMMISSION

Federal Register Volume 80, Issue 148 (August 3, 2015)

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 in NRC's regulations, 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.

[Federal Register Volume 80, Number 148 (Monday, August 3, 2015)]
[Notices]
[Pages 46066-46069]
From the Federal Register Online  [www.thefederalregister.org]
[FR Doc No: 2015-19003]


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NUCLEAR REGULATORY COMMISSION

[Docket No. 50-443; NRC-2015-0184]


NextEra Energy Seabrook, LLC, Seabrook Station, Unit 1

AGENCY: Nuclear Regulatory Commission.

ACTION: Exemption; issuance.

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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 in 
NRC's regulations, 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-2015-0184 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.regulations.gov and search for Docket ID NRC-2015-0184. Address 
questions about NRC dockets to Carol Gallagher; telephone: 301-415-
3463; email: [email protected]. 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 email to [email protected]. The 
ADAMS accession number for each document referenced (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 O1-F21, One White Flint North, 11555 
Rockville Pike, Rockville, Maryland 20852.

FOR FURTHER INFORMATION CONTACT: John G. Lamb, Office of Nuclear 
Reactor Regulation, U.S. Nuclear Regulatory Commission, Washington, DC 
20555-0001; telephone: 301-415-3100, email: [email protected].

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 section 50.60 
of Title 10 of the Code of Federal Regulations (10 CFR), ``Acceptance 
criteria for fracture prevention measures for lightwater nuclear power 
reactors for normal operation,'' pursuant to 10 CFR 50.12, ``Specific 
exemptions.''
    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, 10 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 10 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 10 
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, 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-17444-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 
10 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 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 Technical Specification (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

[[Page 46067]]

degrees Fahrenheit ([deg]F) per hour reactor coolant system (RCS) heat-
up transient, and the 100[emsp14][deg]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[emsp14][deg]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[emsp14][deg]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 NRC 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 NRC staff's 
evaluation of WCAP-17444-P and the licensee's RAI responses. 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 10 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.

III. Discussion

    Pursuant to 10 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. Under 10 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 Head/Vessel 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 10 CFR part 50, appendix G, Table 1. As stated 
previously, 10 CFR 50.12(a)(2) allows the NRC to grant exemptions from 
the requirements of 10 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's 
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-17444-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-17444-P methodology uses a higher material fracture 
toughness, KIc (fracture toughness based on the lower bound 
of static initiation critical values measured as a function of 
temperature) instead of Kla (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 10 CFR part 50, 
appendix G, for pressures greater than 20 percent of the pre-service 
hydrostatic test pressure. The regulations in 10 CFR part 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 (RTNDT) by at 
least 120[emsp14][deg]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 KIc 
material fracture toughness without eliminating the flange requirement 
of 10 CFR part 50, appendix G, would place a restricted operating 
window in the temperature range associated with the flange/closure head 
(i.e., flange RTNDT + 120[emsp14][deg]F). In accordance with 
WCAP-17444-P, the KIc 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-17444-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-17444-P in lieu of 
the

[[Page 46068]]

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 10 CFR part 
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 10 CFR 50.60 and 10 CFR part 50, 
appendix G, is to protect the integrity of the reactor coolant pressure 
boundary. The regulations in 10 CFR part 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 Xl, Appendix G, with additional, more 
restrictive, flange temperature requirements specified in 10 CFR part 
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-17444-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 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 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 10 
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 10 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 10 CFR 51.22(c)(9)(i)
    The NRC staff evaluated whether the exemption involves no 
significant hazards consideration using the standards described in 10 
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-17444 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 part 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-17444,

[[Page 46069]]

the alternative flange temperature requirement of 46[emsp14][deg]F is 
less than the minimum bolt-up temperature of 60[emsp14][deg]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 10 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 10 CFR part 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 10 CFR 51.22(c)(9). Therefore, in accordance with 10 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 
10 CFR 50.60 to permit the use of WCAP-17444-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 10 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.
[FR Doc. 2015-19003 Filed 7-31-15; 8:45 am]
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