[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]


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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