[Federal Register Volume 68, Number 133 (Friday, July 11, 2003)]
[Notices]
[Pages 41405-41407]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 03-17580]



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NUCLEAR REGULATORY COMMISSION

[Docket Nos. 50-369 and 50-370]


Duke Power Company, McGuire Nuclear Station, Units 1 and 2; 
Exemption

1.0 Background

    Duke Power Company (the licensee) is the holder of Facility 
Operating License Nos. NPF-9 and NPF-17 that authorizes operation of 
the McGuire Nuclear Station, Units 1 and 2 (McGuire). 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 two pressurized water reactors located in 
Mecklenburg County, North Carolina.

2.0 Request/Action

    Title 10 of the Code of Federal Regulations (10 CFR) section 
50.60(a), requires that the fracture toughness and material 
surveillance requirements of Appendix G to part 50 must be met for the 
reactor coolant pressure boundary. Appendix G to part 50 requires that 
pressure and temperature (P/T) limits be established for reactor 
pressure vessels (RPVs) during normal operating and hydrostatic or leak 
rate testing conditions. Specifically, section IV.A.2.a of Appendix G 
to 10 CFR part 50 states that ``The appropriate requirements on both 
the pressure-temperature limits and the minimum permissible temperature 
must be met for all conditions.'' Further, section IV.A.2.b of Appendix 
G to 10 CFR part 50 requires that these P/T limits must be at least as 
conservative as limits obtained by following the methods of analysis 
and the margins of safety of Appendix G to section XI of the American 
Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code 
(Code). The current ASME Code of Record for McGuire is the 1995 edition 
through 1996 addenda of the ASME Code. The McGuire Code of Record does 
not incorporate the provisions of ASME Code Case N-641. Although the 
provisions of ASME Code Case N-641 were incorporated into Appendix G to 
section XI of the ASME Code in the 1998 edition through 2000 addenda, 
which is the latest edition and addenda codified in 10 CFR 50.55a, 
McGuire has not adopted this edition and consequently must meet its 
Code of Record to comply with Appendix G to part 50. Therefore, in this 
case, the licensee is still required to obtain an exemption to apply 
Code Case N-641.
    In order to address provisions of amendments to the McGuire 
Technical Specification (TS) P/T limit curves, the licensee requested 
in its submittal dated December 12, 2002, as supplemented by letters 
dated March 27 and April 23, 2003, that the NRC staff exempt McGuire 
from application of specific requirements of 10 CFR 50.60 and Appendix 
G to 10 CFR part 50, and substitute the use of ASME Code Case N-641. 
ASME Code Case N-641 permits the use of an alternate reference fracture 
toughness curve for RPV materials and permits the postulation of a 
circumferentially-oriented flaw for the evaluation of circumferential 
RPV welds when determining the P/T limits. The proposed exemption 
request is consistent with, and is needed to support, the McGuire TS 
amendment that was contained in the same submittal. The proposed 
McGuire TS amendment will revise the P/T limits for heatup, cooldown, 
and inservice test limitations for the reactor coolant system (RCS) 
through 34 effective full power years of operation.

Code Case N-641

    The licensee has proposed an exemption to allow the use of ASME 
Code Case N-641 in conjunction with Appendix G to ASME section XI, 10 
CFR 50.60(a) and 10 CFR part 50, Appendix G, to establish the P/T 
limits for the McGuire, Units 1 and 2 RPVs.
    The proposed TS amendment to revise the P/T limits for McGuire, 
Units 1 and 2, relies in part, on the requested exemption. These 
revised P/T limits have been developed using the lower bound 
KIC fracture toughness curve shown in ASME, section XI, 
Appendix A, Figure A-2200-1, in lieu of the lower bound KIA 
fracture toughness curve of ASME, section XI, Appendix G, Figure G-
2210-1, as the basis fracture toughness curve for defining the McGuire 
P/T limits. In addition, the revised P/T limits have been developed 
based on the use of a postulated circumferentially-oriented flaw for 
the evaluation of RPV circumferential welds in lieu of the axially-
oriented flaw that would be required by Appendix G to section XI of the 
ASME Code. The other margins involved with the ASME section XI, 
Appendix G, process of determining P/T limit curves remain unchanged.
    Use of the KIC curve as the basis fracture toughness 
curve for the development of P/T operating limits is technically 
correct. The KIC curve appropriately implements the use of a 
relationship based on static initiation fracture toughness behavior to 
evaluate the controlled heatup and cooldown process of a RPV, whereas 
the KIA fracture toughness curve codified into Appendix G to 
section XI of the ASME Code was developed from more conservative crack 
arrest and dynamic fracture toughness test data. The application of the 
KIA fracture toughness curve was initially codified in 
Appendix G to section XI of the ASME Code in 1974 to provide a 
conservative representation of RPV material fracture toughness. This 
initial conservatism was necessary due to the limited knowledge of RPV 
material behavior in 1974. However, additional knowledge has been 
gained about RPV materials that demonstrates the lower bound on 
fracture toughness provided by the KIA fracture toughness 
curve is well beyond the margin of safety required to protect the 
public health and safety from potential RPV failure.
    Likewise, the use of a postulated circumferentially-oriented flaw 
in lieu of an axially-oriented one for the evaluation of a 
circumferential RPV weld is more technically correct. The size of flaw 
required to be postulated for P/T limit determination has a depth of 
one-quarter of the RPV wall thickness and a length six times the depth. 
Based on the direction of welding during the fabrication process, the 
only technically reasonable orientation for such a large flaw is for 
the plane of the flaw to be circumferentially-oriented (i.e., parallel 
to the direction of welding). Prior to the development of ASME Code 
Case N-641 (and the similar ASME Code Case N-588), the required 
postulation of an axially-oriented flaw for the evaluation of a 
circumferential RPV weld has provided an additional, unnecessary level 
of conservatism to the overall evaluation.
    In addition, P/T limit curves based on the KIC fracture 
toughness curve and postulation of a circumferentially-oriented flaw 
for the evaluation of RPV circumferential welds will enhance overall 
plant safety by expanding the P/T operating window with the greatest 
safety benefit being in the region of low temperature operations. The 
operating window through which the operator heats up and cools down the 
RCS is determined by the difference between the maximum allowable 
pressure determined by Appendix G of ASME section XI, and the minimum 
required pressure for the reactor coolant pump seals adjusted for 
instrument uncertainties. A narrow operating window could potentially 
have an adverse safety impact by increasing the possibility of 
inadvertent overpressure protection system actuation due to

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pressure surges associated with normal plant evolutions such as RCS 
pump starts and swapping operating charging pumps with the RCS in a 
water-solid condition.
    Since application of ASME Code Case N-641 provides appropriate 
procedures to establish maximum postulated defects and to evaluate 
those defects in the context of establishing RPV P/T limits, this 
application of the Code Case maintains an adequate margin of safety for 
protecting RPV materials from brittle failure. The NRC staff has 
reviewed the exemption request submitted by the licensee and has 
concluded that an exemption should be granted from the requirements of 
10 CFR 50.60 and section IV.A.2.b of Appendix G to 10 CFR part 50 to 
permit the licensee to use the provisions of ASME Code Case N-641 for 
the purpose of developing the McGuire Units 1 and 2 RPV P/T limit 
curves. However, the NRC staff does not agree with the special 
circumstances cited by the licensee in its December 12, 2002, 
application regarding the basis for granting the exemption. The NRC 
staff did not conclude that the circumstances cited above constitute 
``undue hardship or other costs that are significantly in excess of 
those contemplated when the regulation was adopted, or that are 
significantly in excess of those incurred by others similarly 
situated,'' pursuant to 10 CFR 50.12(a)(2)(iii). Rather, the NRC staff 
concluded that the application of the technical provisions of ASME Code 
Case N-641 provided sufficient margin in the development of RPV P/T 
limit curves such that the underlying purpose of the regulations, 
Appendix G to 10 CFR part 50, will continue to be met and that the 
specific conditions required by the regulations (i.e., use of all 
provisions in Appendix G to section XI of the ASME Code) were not 
necessary. Therefore, the NRC staff grants the requested exemption to 
the licensee based on the special circumstances of 10 CFR 
50.12(a)(2)(ii), ``[a]pplication 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.''
    In summary, the ASME section XI, Appendix G, procedure was 
conservatively developed based on the level of knowledge existing in 
1974 concerning reactor coolant pressure boundary materials and the 
estimated effects of operation. Since 1974, the level of knowledge 
about the fracture mechanics behavior of RCS materials has been greatly 
expanded, especially regarding the effects of radiation embrittlement 
and the understanding of fracture toughness properties under static and 
dynamic loading conditions. The NRC staff concurs that this increased 
knowledge permits relaxation of the ASME section XI, Appendix G 
requirements by application of ASME Code Case N-641, while maintaining, 
pursuant to 10 CFR 50.12(a)(2)(ii), the underlying purpose of the ASME 
Code and the NRC regulations to ensure an acceptable margin of safety 
against brittle failure of the RPV.
    The NRC staff has reviewed the exemption request submitted by the 
licensee and has concluded that an exemption should be granted from the 
requirements of 10 CFR 50.60(a) and section IV.A.2.b of Appendix G to 
10 CFR part 50 to permit the licensee to utilize the provisions of ASME 
Code Case N-641 for the purpose of developing McGuire Units 1 and 2 RPV 
P/T limit curves.

3.0 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.
    Special circumstances, pursuant to 10 CFR 50.12(a)(2)(ii), are 
present in that continued operation of McGuire, Units 1 and 2, pursuant 
to the requirements of 10 CFR 50.60 and section IV.A.2.b of Appendix G 
to 10 CFR part 50, using P/T curves developed in accordance with ASME 
section XI, Appendix G, without the relief provided by ASME Code Case 
N-641, is not necessary to achieve the underlying purpose of 10 CFR 
50.60 and Appendix G to 10 CFR part 50. Application of ASME Code Case 
N-641 in lieu of the requirements of ASME Code section XI, Appendix G, 
provides an acceptable alternate methodology that will continue to meet 
the underlying purpose of 10 CFR 50.60 and Appendix G to 10 CFR part 
50. The underlying purpose of the regulations in 10 CFR 50.60 and 
Appendix G to 10 CFR part 50 is to provide an acceptable margin of 
safety against brittle failure of the RCS during any condition of 
normal operation to which the pressure boundary may be subjected over 
its service lifetime.
    The NRC staff examined the licensee's rationale to support the 
exemption request, and accepts the licensee's determination that an 
exemption would be required to approve the use of Code Case N-641. The 
NRC staff agrees that the use of ASME Code Case N-641 would meet the 
underlying intent of 10 CFR 50.60 and Appendix G to 10 CFR part 50. The 
NRC staff concludes that the application of the technical provisions of 
ASME Code Case N-641 provides sufficient margin in the development of 
RPV P/T limit curves such that the underlying purpose of the 
regulations (10 CFR 50.60 and Appendix G to 10 CFR part 50) continues 
to be met and that the specific conditions required by the regulations 
(i.e., use of all provisions in Appendix G to section XI of the ASME 
Code) were not necessary. Therefore, the NRC staff concludes that the 
exemption requested by the licensee is justified based on the special 
circumstances of 10 CFR part 50(a)(2)(ii), ``[a]pplication 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.''
    Based upon a consideration of the conservatism that is explicitly 
incorporated into the methodologies of Appendix G to 10 CFR part 50; 
Appendix G to section XI of the ASME Code; and Regulatory Guide 1.99, 
Revision 2; the NRC staff concludes that application of ASME Code Case 
N-641, as described, will provide an adequate margin of safety against 
brittle failure of the RPV. This conclusion is also consistent with the 
determination that the NRC staff has reached for other licensees under 
similar conditions based on the same considerations. Therefore, the NRC 
staff concludes that granting the exemption under the special 
circumstances of 10 CFR 50.12(a)(2)(ii) is appropriate, and that the 
methodology of Code Case N-641 may be used to revise the P/T limits for 
the McGuire, Unit 1 and 2 RPVs.

4.0 Conclusion

    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 
the requirements of 10 CFR 50.60(a), and 10 CFR part 50, Appendix G, 
section IV.A.2.b, to allow application of ASME Code Case N-641 in 
establishing TS requirements for the RPV limits for McGuire, Units 1 
and 2.
    Pursuant to 10 CFR 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 31735).

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    This exemption is effective upon issuance.

    Dated at Rockville, Maryland, this 3rd day of July 2003.

    For the Nuclear Regulatory Commission.
Ledyard B. Marsh,
Acting Director, Division of Licensing Project Management, Office of 
Nuclear Reactor Regulation.
[FR Doc. 03-17580 Filed 7-10-03; 8:45 am]
BILLING CODE 7590-01-P