[Federal Register Volume 80, Number 148 (Monday, August 3, 2015)]
[Notices]
[Pages 46066-46069]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[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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