[Federal Register Volume 68, Number 40 (Friday, February 28, 2003)]
[Notices]
[Pages 9725-9727]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 03-4750]
=======================================================================
-----------------------------------------------------------------------
NUCLEAR REGULATORY COMMISSION
[Docket No. 50-263]
Nuclear Management Company, LLC, Monticello Nuclear Generating
Plant; Exemption
1.0 Background
The Nuclear Management Company, LLC (the licensee), is the holder
of Facility Operating License No. DPR-22 which authorizes operation of
the Monticello Nuclear Generating Plant (MNGP). The license provides,
among other things, that the facility is subject to all rules,
regulations, and orders of the U.S. Nuclear Regulatory Commission (NRC,
the Commission) now or hereafter in effect.
The facility consists of a boiling water reactor located in Wright
County, Minnesota.
2.0 Request/Action
Title 10 of the Code of Federal Regulations (10 CFR) part 50,
Section 50.60(a), requires, in part, that except where an exemption is
granted by the Commission, all light-water nuclear power reactors must
meet the fracture toughness requirements for the reactor coolant
pressure boundary set forth in Appendices G and H to 10 CFR part 50.
Appendix G to 10 CFR part 50 requires that pressure-temperature (P/T)
limits be established for reactor pressure vessels (RPVs) during normal
operating and hydrostatic or leak-rate testing conditions.
Specifically, 10 CFR part 50, Appendix G, states, ``The appropriate
requirements on both the pressure-temperature limits and the minimum
permissible temperature must be met for all conditions.'' Appendix G of
10 CFR part 50 specifies that the requirements for these limits are the
American Society of Mechanical Engineers Boiler and Pressure Vessel
Code (ASME Code), Section XI, Appendix G, limits.
To address provisions of a proposed amendment to change the P/T
limits in the Monticello Technical Specifications, the licensee
requested an exemption from the application of specific requirements of
10 CFR part 50, Section 50.60(a) and Appendix G, to allow the use of
ASME Code Case N-640, ``Alternative Reference Fracture Toughness for
Development of P-T Limit Curves.'' ASME Code Case N-640 permits the use
of alternate reference fracture toughness (i.e., use of
``KIC fracture toughness curve'' instead of ``KIA
fracture toughness curve,'' where KIC and KIA are
``Reference Stress Intensity Factors,'' as defined in ASME Code,
Section XI, Appendices A and G, respectively) for RPV materials in
determining the P/T limits. Since the KIC fracture toughness
curve shown in ASME Code, Section XI, Appendix A, Figure A-2200-1,
provides greater allowable fracture toughness than the corresponding
KIA fracture toughness curve of ASME Code, Section XI,
Appendix G, Figure G-2210-1, using ASME Code Case N-640 to establish
the P/T limits would be less conservative than the methodology
currently endorsed by 10 CFR part 50, Appendix G. Therefore, an
exemption is required to use ASME Code Case N-640.
The proposed exemption is needed to allow the licensee to implement
ASME Code Case N-640 in order to revise the method used to determine
RPV P/T limits because continued use of the present curves
unnecessarily restricts the P/T operating windows for the reactor
coolant system (RCS). Since the P/T operating window is defined by the
P/T operating and test limit curves developed in accordance with the
ASME Code, Section XI, Appendix G, procedure, continued operation of
MNGP with the current P/T curves without the relief provided by ASME
Code Case N-640 would unnecessarily require that the RPV be maintained
at a temperature exceeding 212 [deg]F in a limited operating window
during pressure tests. Consequently, steam
[[Page 9726]]
vapor hazards would continue to be a safety concern for personnel
conducting inspections in the primary containment. Implementation of
the proposed P/T curves, as allowed by ASME Code Case N-640, would not
significantly reduce the margin of safety and would eliminate steam
vapor hazards by allowing inspections in the primary containment to be
conducted at a lower coolant temperature.
3.0 Discussion
Pursuant to 10 CFR part 50, Section 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. These special
circumstances include the following:
(1) Pursuant to 10 CFR part 50, Section 50.12(a)(2)(ii), the
circumstance that application of the regulation in the particular
circumstances would not serve the underlying purpose of the rule or is
not necessary to achieve the underlying purpose of the rule. ASME Code,
Section XI, Appendix G, provides procedures for determining the
allowable loading on the RPV and is approved for that purpose by 10 CFR
part 50, Appendix G. Application of these procedures in the
determination of P/T operating and test curves satisfies the underlying
requirement that (1) the reactor coolant pressure boundary be operated
in a regime having a sufficient margin to ensure, when stressed, the
vessel boundary behaves in a ductile manner and the probability of a
rapidly propagating fracture is minimized; and (2) P/T operating and
test limit curves provide an adequate margin in consideration of
uncertainties in determining the effects of irradiation on material
properties. The ASME Code, Section XI, Appendix G, procedure was
conservatively developed based upon the level of knowledge existing in
1974 concerning RPV materials and the estimated effects of operation.
Since 1974, the level of knowledge concerning these topics has greatly
expanded. This increased knowledge permits relaxation of the ASME Code,
Section XI, Appendix G, requirements via application of ASME Code Case
N-640, while maintaining the underlying purpose of the ASME Code and
NRC regulations to ensure an acceptable margin of safety.
(2) Pursuant to 10 CFR part 50, Section 50.12(a)(2)(iii),
compliance would result in undue hardship or other costs that are
significantly in excess of those contemplated when the regulation was
adopted, or those incurred by others similarly situated. The P/T
operating window from the RCS is defined by the P/T operating and test
limit curves developed in accordance with the ASME Code, Section XI,
Appendix G procedure. As previously noted, continued operation of MNGP
with these P/T curves without the relief provided by ASME Code Case N-
640 would unnecessarily restrict the P/T operating window. This
restriction requires the MNGP Operations Staff to maintain a high
temperature during pressure tests and also subjects the inspection
personnel to increased safety hazards while conducting inspections of
systems with the potential for steam leaks in a primary containment at
elevated temperatures.
This constitutes an unnecessary burden that can be alleviated by
the application of ASME Code Case N-640 in the development of the
proposed P/T limit curves. Implementation of the proposed P/T limit
curves, as allowed by ASME Code Case N-640, would not significantly
reduce the margin of safety.
(3) Pursuant to 10 CFR part 50, Section 50.12(a)(2)(v), compliance
will provide ``only temporary relief from the applicable regulation and
the licensee . . . has made good faith efforts to comply with the
regulation.'' The NRC staff finds that the licensee for MNGP has made a
good faith effort to comply with the regulation, and the requested
exemption provides only temporary relief from the applicable regulation
until such time that the NRC generically approves ASME Code Case N-640
for use by the nuclear industry.
The NRC staff examined the licensee's rationale to support the
exemption request and concluded that the use of the ASME Code Case N-
640 would satisfy 10 CFR part 50, Section 50.12(a)(1) as follows:
(1) The requested exemption is authorized by law: No law exists
which precludes the activities covered by this exemption request. The
regulation 10 CFR part 50, Section 50.60(b), allows the use of
alternatives to 10 CFR part 50, Appendices G and H, when an exemption
is granted by the Commission pursuant to 10 CFR part 50, Section 50.12.
(2) The requested exemption does not present an undue risk to the
public health and safety: ASME Code Case N-640 permits the use of
alternate reference fracture toughness (KIC fracture
toughness curve instead of KIA fracture toughness curve) for
RPV Materials in determining the P/T limits. The KIC
fracture toughness curve is shown in ASME Code, Section XI, Appendix A,
Figure A-2200-1, and provides greater allowable fracture toughness than
the corresponding KIA fracture toughness curve of ASME Code,
Section XI, Appendix G, Figure G-2210-1. The other margins involved
with the ASME Code, Section XI, Appendix G process of determining P/T
limit curves remain unchanged.
Use of the KIC curve in determining the lower bound
fracture toughness in the development of the P/T operating limits curve
is more technically correct than the KIA curve. The
KIC curve models the slow heatup and cooldown process of a
reactor vessel. The KIC curve appropriately implements the
use of static initiation fracture toughness behavior to evaluate the
controlled heatup and cooldown process of a RPV.
Use of this approach is justified by the initial conservatism of
the KIA curve when the curve was codified in 1974. This
initial conservatism was necessary due to limited knowledge of RPV
material fracture toughness. Since 1974, additional knowledge has been
gained about the fracture toughness of vessel materials and their
fracture response to applied loads. The additional knowledge
demonstrates that the lower bound fracture toughness provided by the
KIA curve is well beyond the margin of safety required to
protect against potential RPV failure. The lower bound KIC
fracture toughness provides an adequate margin of safety to protect
against potential RPV failure and does not present an undue risk to
public health and safety.
P/T limit curves based on the KIC fracture toughness
limits will enhance overall plant safety by opening the P/T operating
window. Since the RCS P/T operating window is defined by the P/T
operating and test limit curves developed in accordance with the ASME
Code, Section XI, Appendix G, procedure, continued operation of MNGP
with these P/T limit curves without using ASME Code Case N-640 would
unnecessarily require the RPV to be maintained at a temperature
exceeding 212 [deg]F in a limited operating window during the pressure
test. Consequently, steam vapor hazards would continue to be one of the
safety concerns for personnel conducting inspections in the primary
containment.
Use of the revised curves would result in a reduction in the
challenges to operators in maintaining a high temperature in a limited
operating window and would eliminate steam vapor hazards by allowing
inspections in primary containment to be conducted
[[Page 9727]]
at lower coolant temperature, while continuing to provide an adequate
margin of safety.
(3) The requested exemption will not endanger the common defense
and security: The common defense and security are not endangered by
this exemption request.
On the basis of the conservatism that is explicitly incorporated
into the methodologies of 10 CFR part 50, Appendix G, and ASME Code,
Section XI, Appendix G, the NRC staff concludes that application of
ASME Code Case N-640, as described above, would provide an adequate
margin of safety against brittle failure of the RPV. This is also
consistent with the determination that the NRC staff has reached for
other licensees under similar conditions based upon the same
considerations. The NRC staff has previously granted exemptions to use
ASME Code Case N-640 for the Quad Cities Nuclear Power Station and the
Limerick Generating Station Unit 1 where the NRC staff concluded that
application of ASME Code Case N-640 would provide adequate safety
margins consistent with 10 CFR part 50, Appendix G, and Appendix G to
ASME Code, Section XI. In the same cases, the NRC staff also concluded
that relaxation of the methodology in Appendix G to ASME Code, Section
XI, by application of ASME Code Case N-640 is acceptable, and pursuant
to 10 CFR 50.12(a)(2)(ii), would maintain the underlying purpose of the
NRC regulations to ensure an acceptable margin of safety for the Quad
Cities and Limerick Generating Station Unit 1 RPVs and RCSs. The
licensee's proposal to use ASME Code Case N-640 for generation of the
MNGP P/T limit curves is predicated on the same technical basis as was
used for generation of the P/T limits for Quad Cities and Limerick
Generating Station Unit 1.
Therefore, the NRC staff concludes that pursuant to 10 CFR part 50,
Section 50.12(a)(1), and 10 CFR part 50, Section 50.12(a)(2)(ii),
(iii), and (v), granting an exemption is appropriate and that the
methodology of ASME Code Case N-640 may be used to revise the P/T
limits for MNGP.
4.0 Conclusion
Accordingly, the Commission has determined that, pursuant to 10 CFR
part 50, Section 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
Nuclear Management Company, LLC, an exemption from the requirements of
10 CFR part 50, Section 50.60(a) and 10 CFR part 50, Appendix G, for
MNGP.
Pursuant to 10 CFR part 50, Section 51.32, the Commission has
determined that the granting of this exemption will not have a
significant effect on the quality of the human environment (68 FR
8052).
This exemption is effective upon issuance.
Dated at Rockville, Maryland, this 21st day of February 2003.
For the Nuclear Regulatory Commission.
John A. Zwolinski,
Director, Division of Licensing Project Management, Office of Nuclear
Reactor Regulation.
[FR Doc. 03-4750 Filed 2-27-03; 8:45 am]
BILLING CODE 7590-01-P