[Federal Register Volume 66, Number 89 (Tuesday, May 8, 2001)]
[Notices]
[Pages 23278-23279]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 01-11567]


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NUCLEAR REGULATORY COMMISSION

[Docket Nos. 50-338 and 50-339]


Virginia Electric and Power Company, North Anna Power Station 
Units 1 and 2; Exemption

1.0  Background

    The Virginia Electric and Power Company (the licensee) is the 
holder of Facility Operating Licenses NPF-4 and NPF-7, which authorize 
operation of the North Anna Power Station, Units 1 and 2. The licenses 
provide, 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 
Louisa County in the Commonwealth of Virginia.

2.0  Purpose

    Title 10 of the Code of Federal Regulations (10 CFR) part 50, 
Appendix G requires that pressure-temperature (P-T) limits be 
established for reactor pressure vessels (RPVs) during normal 
operating, and hydrostatic pressure or leak testing conditions. 
Specifically, 10 CFR part 50, Appendix G states that ``[t]he 
appropriate requirements on * * * the pressure-temperature limits and 
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 (ASME) Code, 
Section XI, Appendix G Limits. RG 1.99, Rev. 2, provides guidance for 
implementing 10 CFR Part 50, Appendix G. In GL 88-11, the NRC staff 
advised licensees that the staff would use RG 1.99, Rev. 2, to review 
P-T limit curves. RG 1.99, Rev. 2, contains conservative methodologies 
for determining the increase in transition temperature and the decrease 
in upper-shelf energy resulting from neutron radiation.
    To address provisions of amendments to the technical specifications 
(TS) regarding the P-T limits, low temperature overpressure protection 
(LTOP) system setpoints, and LTOP system effective temperature 
(Tenable), the licensee requested in its submittal dated 
June 22, 2000, as supplemented by letters dated September 19, 2000, and 
January 4, February 14, March 13, March 22, and April 11, 2001, that 
the staff exempt North Anna Units 1 and 2 from application of specific 
requirements of 10 CFR part 50, appendix G, and substitute use of ASME 
Code Case N-641. Code Case N-641 permits the use of an alternate 
reference fracture toughness (KIC fracture toughness curve 
instead of KIa fracture toughness curve) for reactor vessel 
materials in determining the P-T limits, LTOP system setpoints and 
Tenable, and provides for plant-specific evaluation of 
Tenable. Since the KIC fracture toughness curve 
shown in ASME Section XI, Appendix A, Figure A-2200-1 (the 
KIC fracture toughness curve) provides greater allowable 
fracture toughness than the corresponding KIa fracture 
toughness curve of ASME Section XI, Appendix G, Figure G-2210-1 (the 
KIa fracture toughness curve) and a plant-specific 
evaluation of Tenable would give lower values of 
Tenable than use of a generic bounding evaluation for 
Tenable, use of Code Case N-641 for establishing the P-T 
limits, LTOP system setpoints and Tenable would be less 
conservative than the methodology currently endorsed by 10 CFR Part 50, 
Appendix G and, therefore, an exemption to apply the Code Case would be 
required by 10 CFR 50.60. Although the use of the KIC 
fracture toughness curve in ASME Code Case N-641 was recently 
incorporated into appendix G to Section XI of the ASME Code, an 
exemption is still needed because 10 CFR part 50, appendix G requires 
the licensee's analysis to use an edition and addenda of Section XI of 
the ASME Code incorporated by reference into 10 CFR 50.55a, i.e., the 
editions through 1995 and addenda through the 1996 addenda (which do 
not include the provisions of Code Case N-641).
    The proposed amendments submitted by the licensee will revise the 
P-T limits of TS 3/4.4.9 related to the heatup and cooldown of the 
reactor coolant system (RCS), the LTOP system setpoints and 
Tenable for the LTOP system, for operation to 32.3 effective 
full power years (EFPY) for Unit 1 and 34.3 EFPY for Unit 2.

ASME Code Case N-641

    The licensee has proposed an exemption to allow use of ASME Code 
Case N-641 in conjunction with ASME Section XI, 10 CFR 50.60(a) and 10 
CFR part 50, appendix G, to determine the P-T limits, LTOP system 
setpoints and Tenable.
    The proposed amendments to revise the P-T limits, LTOP system 
setpoints and Tenable for North Anna Units 1 and 2 rely in 
part on the requested exemption. The revised P-T limits, LTOP system 
setpoints and Tenable have been developed using the 
KIc fracture toughness curve, in lieu of the KIa 
fracture toughness curve, as the lower bound for fracture toughness of 
the RPV materials.
    Use of the KIc curve in determining the lower bound 
fracture toughness of RPV steels is more technically correct than use 
of the KIa curve since the rate of loading during a heatup 
or cooldown is slow and is more representative of a static condition 
than a dynamic condition. The KIc curve appropriately 
implements the use of static initiation fracture toughness behavior to 
evaluate the controlled heatup and cooldown process of a reactor 
vessel. The staff has required use of the conservatism of the 
KIa curve since 1974, when the curve was adopted by the ASME 
Code. This conservatism was initially necessary due to the limited 
knowledge of the fracture toughness of RPV materials at that time. 
Since 1974, additional knowledge has been gained about RPV materials, 
which demonstrates that the lower bound on fracture toughness provided 
by the KIa curve greatly exceeds the margin of safety 
required to protect the public health and safety from potential RPV 
failure. In addition, P-T curves, LTOP setpoints, and 
Tenable based on the KIc 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.
    Since an unnecessarily reduced P-T operating window can reduce 
operator flexibility without just basis, implementation of the proposed 
P-T curves, LTOP setpoints, and Tenable as allowed by ASME 
Code Case N-641 may result in enhanced safety during critical plant 
operational periods, specifically heatup and cooldown conditions. Thus, 
pursuant to 10 CFR 50.12(a)(2)(ii), the underlying purpose of 10 CFR 
50.60 and appendix G to 10 CFR part 50 will continue to be served.
    In summary, the ASME Section XI, Appendix G, procedure was 
conservatively developed based on the level of knowledge existing in 
1974 concerning RPV materials and the estimated effects of operation. 
Since 1974, the level of knowledge about these topics has been greatly 
expanded. The 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,

[[Page 23279]]

pursuant to 10 CFR 50.12(a)(2)(ii), the underlying purpose of the NRC 
regulations to ensure an acceptable margin of safety.

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 staff accepts the 
licensee's determination that an exemption would be required to approve 
the use of Code Case N-641. The staff examined the licensee's rationale 
to support the exemption request and concurs that the use of the Code 
case would meet the underlying intent of these regulations. Based upon 
a consideration of the conservatism that is explicitly incorporated 
into the methodologies of 10 CFR part 50, appendix G; Appendix G of the 
Code; and Regulatory Guide 1.99, Revision 2, as discussed above, the 
staff concludes that application of the Code case as described would 
provide an adequate margin of safety against brittle failure of the 
RPV. This conclusion is also consistent with the determinations that 
the staff has reached for other licensees under similar conditions 
based on the same considerations.
    Therefore, the staff concludes that granting an exemption under the 
special circumstances of 10 CFR 50.12(a)(2)(ii) is appropriate and that 
the methodologies of Code Case N-641 may be used to revise the P-T 
limits, LTOP setpoints, and Tenable for North Anna Power 
Station, Units 1 and 2.

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, and is, otherwise, in the 
public interest. Therefore, the Commission hereby grants the licensee 
an exemption from the requirements of 10 CFR part 50, appendix G, for 
North Anna Power Station, 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 (66 FR 22018).
    This exemption is effective upon issuance.

    Dated at Rockville, Maryland, this 2nd day of May 2001.

    For the Nuclear Regulatory Commission.
John A. Zwolinski,
Director, Division of Licensing Project Management, Office of Nuclear 
Reactor Regulation.
[FR Doc. 01-11567 Filed 5-7-01; 8:45 am]
BILLING CODE 7590-01-P