[Federal Register Volume 68, Number 150 (Tuesday, August 5, 2003)]
[Notices]
[Pages 46238-46239]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 03-19886]



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NUCLEAR REGULATORY COMMISSION

[Docket No. 50-328]


Tennessee Valley Authority, Sequoyah Nuclear Plant, Unit 2; 
Exemption

1.0 Background

    Tennessee Valley Authority (TVA, the licensee) is the holder of 
Facility Operating License No. DRP-79 which authorizes operation of 
Sequoyah Nuclear Power Station, Unit 2 (SQN2). 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 pressurized water-reactor located on 
TVA's Sequoyah site, which is located in Hamilton County, Tennessee.

2.0 Request/Action

    Title 10 of the Code of Federal Regulations (10 CFR), part 50, 
appendix G, which is invoked by 10 CFR 50.60, 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, appendix G to 10 CFR part 50 states that 
``[t]he appropriate requirements on . . . the pressure-temperature 
limits and minimum permissible temperature must be met for all 
conditions,'' and ``[t]he pressure-temperature limits identified as 
`ASME Appendix G limits' . . . require that the limits must be at least 
as conservative as limits obtained by following the methods of analysis 
and the margins of safety of Appendix G of Section XI of the ASME 
Code.'' Appendix G of 10 CFR part 50 also specifies that the Editions 
and Addenda of the ASME Boiler and Pressure Vessel (B&PV) Code which 
are incorporated by reference in 10 CFR 50.55a apply to the 
requirements in appendix G to 10 CFR part 50. The NRC endorsed Editions 
and Addenda of the ASME B&PV Code through the 1998 Edition and 2000 
Addenda. However, TVA has currently incorporated the 1995 Edition 
through the 1996 Addenda of the ASME B&PV Code into the SQN2 licensing 
basis for defining the ASME B&PV Code requirements which apply to the 
unit's ASME B&PV Code, Section XI program. Hence, with respect to the 
statements from appendix G to 10 CFR part 50 referenced above, it is 
the 1995 Edition through 1996 Addenda of ASME B&PV Code, Section XI, 
Appendix G which apply for SQN2. Finally, 10 CFR 50.60(b) states that, 
``[p]roposed alternatives to the described requirements in [Appendix G] 
of this part or portions thereof may be used when an exemption is 
granted by the Commission under [10 CFR 50.12].''
    TVA requested in its submittal dated September 6, 2002, as 
supplemented by letters dated December 19, 2002, and June 24, 2003, 
that the staff exempt SQN2 from application of specific requirements of 
appendix G to 10 CFR part 50, and substitute use of ASME B&PV Code Case 
N-640. ASME B&PV Code Case N-640 permits the use of an alternate 
reference fracture toughness curve for RPV materials for use in 
determining the P-T limits. The exemption request is consistent with, 
and needed to support, a SQN2 license amendment request that was 
submitted on June 5, 2003, to modify the P-T limit curves in the 
facility's Technical Specifications (TS). The SQN2 license amendment 
request will revise the P-T limits for heatup, cooldown, and inservice 
test limitations for the reactor coolant system (RCS) to 32 effective 
full power years of operation.

Code Case N-640

    The licensee has proposed an exemption to allow use of ASME Code 
Case N-640 in conjunction with ASME Section XI, Appendix G, 10 CFR 
50.60(a) and 10 CFR part 50, appendix G, to establish P-T limits for 
the SQN2 RPV. The 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 
SQN2 P-T limits. 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 more technically 
correct than use of the KIA curve. 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 an 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 which demonstrates that 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 brittle failure. Application of the 
provisions of ASME Code Case N-640 will result in the implementation of 
P-T limit curves having sufficient margin to ensure that, when 
stressed, the reactor pressure vessel will behave in a nonbrittle 
manner and that the probability of rapidly propagating brittle fracture 
is extremely low.
    In addition, P-T limit curves based on the KIC fracture 
toughness curve will enhance overall plant safety by opening the P-T 
operating window with the greatest safety benefit 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 pressure surges associated with normal plant evolutions such as RCS 
pump starts or swapping operating charging pumps with the RCS in a 
water-solid condition.
    Therefore, the licensee concluded that these considerations were 
special circumstances pursuant to 10 CFR 50.12(a)(2)(ii), and supported 
the requested exemption to utilize the provisions of ASME B&PV Code 
Case N-640 in the development of SQN2 RPV P-T limit curves.
    The NRC staff has reviewed the exemption request submitted by TVA 
and has concluded that an exemption should be granted to permit the 
licensee to utilize the provisions of ASME B&PV Code Case N-640 for the 
purpose of developing SQN2 RPV P-T limit curves. The NRC staff agrees 
that special circumstances pursuant to 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,'' exist. The NRC staff 
concurs that the licensee may acceptably apply the provisions of

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ASME Code Case N-640 to relax the requirements found in the 1995 
Edition through 1996 Addenda of the ASME B&PV Code, Section XI, 
Appendix G, while maintaining, pursuant to 10 CFR50.12(a)(2)(ii), the 
underlying purpose of the ASME B&PV Code and the NRC regulations to 
ensure that adequate margins of safety exist to protect the RCS from 
the potential for brittle failure.

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. The NRC staff accepts the 
licensee's determination that an exemption would be required to approve 
the use of ASME B&PV Code Case N-640. The NRC staff concluded that the 
use of ASME B&PV Code Case N-640 would meet the underlying intent of 
appendix G to 10 CFR part 50. Based upon a consideration of the 
conservatism that is explicitly incorporated into the methodologies of 
appendix G to 10 CFR part 50, the staff concluded that application of 
ASME Code Case N-640 as described would provide an adequate margin of 
safety against brittle failure of the RPV. This is also consistent with 
the determination that the staff has reached for other licensees under 
similar conditions based on the same considerations. Therefore, the 
staff concludes that requesting the exemption under the special 
circumstances of 10 CFR 50.12(a)(2)(ii) is appropriate and that the 
methodology of Code Case N-640 may be used to revise the P-T limits for 
the SQN2 RPV.

4.0 Conclusion

    Accordingly, the Commission has determined that, pursuant to 10 CFR 
50.12(a), the exemption is authorized by law, will not endanger life or 
property or common defense and security. Also, special circumstances 
are present. Therefore, the Commission hereby grants Tennessee Valley 
Authority an exemption from the requirements of appendix G to 10 CFR 
part 50 for the development of P-T limit curves for the SQN2 RPV.
    Pursuant to 10 CFR 51.32, the Commission has determined that the 
granting of this exemption will not result in any significant effect on 
the quality of the human environment (68 FR 44550).
    This exemption is effective upon issuance.

    Dated at Rockville, Maryland, this 30th Day of July 2003.
    For The Nuclear Regulatory Commission.
Ledyard B. Marsh,
Director, Division of Licensing Project Management, Office of Nuclear 
Reactor Regulation.
[FR Doc. 03-19886 Filed 8-4-03; 8:45 am]
BILLING CODE 7590-01-P