[Federal Register Volume 66, Number 78 (Monday, April 23, 2001)]
[Notices]
[Pages 20486-20487]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 01-9953]


-----------------------------------------------------------------------

NUCLEAR REGULATORY COMMISSION

[Docket No. 50-271]


Vermont Yankee Nuclear Power Corporation, Vermont Yankee Nuclear 
Power Station; Exemption

1.0 Background

    The Vermont Yankee Nuclear Power Corporation (VYNPC, the licensee) 
is the holder of Facility Operating License No. DPR-28 which authorizes 
operation of the Vermont Yankee Nuclear Power Station (Vermont Yankee). 
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 Windham 
County, Vermont.

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 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; ``must be at least as 
conservative as the limits obtained by following the methods of 
analysis and the margins of safety of appendix G of Section XI of the 
American Society of Mechanical Engineers Boiler and Pressure Vessel 
Code (ASME Code).'' The approved methods of analysis in appendix G of 
Section XI require the use of KIa fracture toughness curve 
in the determination of the P-T limits.
    By letter dated December 19, 2000, VYNPC submitted a license 
amendment request to update the P-T limit curves for Vermont Yankee. In 
the license amendment request, VYNPC also requested NRC approval for an 
exemption to use Code Cases N-588 and N-640 as alternative methods for 
complying with the fracture toughness requirements in 10 CFR part 50, 
appendix G, for generating the P-T limit curves. Requests for such 
exemptions may be submitted pursuant to 10 CFR 50.60(b), which allows 
licensees to use alternatives to the requirements of 10 CFR part 50, 
appendices G and H, if the Commission grants an exemption pursuant to 
10 CFR 50.12 to use the alternatives.

Code Case N-588

    The methods of ASME Code Case N-588 provide alternative methods for 
calculating the stress intensities due to membrane stresses (i.e., 
KIm values) and thermal stresses (i.e., KIt 
values) for both axially and circumferentially oriented flaws. However, 
the alternative methods in Code Case N-588 for calculating the 
KIm values and KIt values for axially oriented 
flaws are equivalent to those specified in the 1995 Edition of appendix 
G to Section XI of the ASME Code for axially oriented flaws. Appendix G 
of 10 CFR part 50 still requires that licensed utilities postulate the 
occurrence of an axially oriented flaw in each of the base metal 
materials and axial weld materials used to fabricate their RPVs. 
Exemptions to use ASME Code Case N-588 are, therefore, not necessary 
for RPVs that are limited in their beltline regions by base-metal or 
axial weld metal materials, because using the methods in the Code Case 
would not provide any benefit for evaluating the postulated axial flaws 
over those specified in the 1995 Edition of appendix G to Section XI of 
the

[[Page 20487]]

ASME Code. Since the Vermont Yankee RPV is currently limited by Plate 
No. I-14 (material heat 76492), use of Code Case N-588 does not provide 
benefit for VYNPC. Therefore, on February 2, 2001, as part of the 
request for additional information (RAI) for Vermont Yankee's proposed 
P-T limits, the staff requested that VYNPC withdraw its exemption 
request to apply Code Case N-588 to the P-T limit calculations or 
provide additional information that demonstrates a reduction in 
unnecessary burden. In a letter dated February 13, 2001, and as 
confirmed in VYNPC's RAI response dated February 23, 2001, VYNPC 
withdrew the Code Case N-588 exemption request.

Code Case N-640 (formerly Code Case N-626)

    Code Case N-640 permits application of the lower bound static 
initiation fracture toughness value equation (KIc equation) 
as the basis for establishing the curves in lieu of using the lower 
bound crack arrest fracture toughness value equation (i.e., the 
KIa equation, which is based on conditions needed to arrest 
a dynamically propagating crack, and which is the method invoked by 
appendix G to Section XI of the ASME Code). Use of the KIc 
equation in determining the lower bound fracture toughness in the 
development of the P-T operating limits curve is more technically 
correct than the use of the KIa equation 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 
equation appropriately implements the use of the static initiation 
fracture toughness behavior to evaluate the controlled heatup and 
cooldown process of a reactor vessel. However, since use of Code Case 
N-640 constitutes an alternative to the requirements of appendix G, 
licensees need staff approval to apply the Code Case methods to the P-T 
limit calculations.

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 and 
safety, and are consistent with the common defense and security; and 
(2) when special circumstances are present. Special circumstances are 
present whenever, according to 10 CFR 50.12 (a)(2)(ii), ``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.''

Code Case N-640 (formerly Code Case N-626)

    VYNPC has requested, pursuant to 10 CFR 50.60(b), an exemption to 
use ASME Code Case N-640 (previously designated as Code Case N-626) as 
the basis for establishing the P-T limit curves. Appendix G of 10 CFR 
part 50 has required use of the initial conservatism of the 
KIa equation since 1974 when the equation was codified. This 
initial conservatism was necessary due to the limited knowledge of RPV 
materials. Since 1974, the industry has gained additional knowledge 
about RPV materials, which demonstrates that the lower bound on 
fracture toughness provided by the KIc equation is well 
beyond the margin of safety required to protect the public health and 
safety from potential RPV failure. In addition, the RPV 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.
    The ASME Working Group on Operating Plant Criteria (WGOPC) has 
concluded that application of Code Case N-640 to plant P-T limits is 
still sufficient to ensure the structural integrity of RPVs during 
plant operations. The staff has concurred with ASME's determination. 
The staff had concluded that application of Code Case N-640 would not 
significantly reduce the safety margins required by 10 CFR part 50, 
appendix G. The staff also concluded that relaxation of the 
requirements of appendix G to the Code by application of Code Case N-
640 is acceptable and would maintain, pursuant to 10 CFR 
50.12(a)(2)(ii), the underlying purpose of the NRC regulations to 
ensure an acceptable margin of safety for the Vermont Yankee RPV and 
reactor coolant pressure boundary (RCPB). Therefore, the staff 
concludes that Code Case N-640 is acceptable for application to the 
Vermont Yankee P-T limits.
    The staff has determined that VYNPC has provided sufficient 
technical bases for using the methods of Code Case N-640 for the 
calculation of the P-T limits for the Vermont Yankee RCPB. The staff 
has also determined that application of Code Case N-640 to the P-T 
limit calculations will continue to serve the purpose in 10 CFR part 
50, appendix G, for protecting the structural integrity of the Vermont 
Yankee RPV and RCPB. In this case, since strict compliance with the 
requirements of 10 CFR part 50, appendix G, is not necessary to serve 
the underlying purpose of the regulation, the staff concludes that 
application of Code Case N-640 to the P-T limit calculations meets the 
special circumstance provisions stated in 10 CFR 50.12(a)(2)(ii), for 
granting this exemption to the regulation.

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. Also, special circumstances are present. Therefore, 
the Commission hereby grants VYNPC an exemption from the requirements 
of 10 CFR part 50, appendix G, for Vermont Yankee.
    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 18514).
    This exemption is effective upon issuance.

    Dated at Rockville, Maryland, this 16th day of April 2001.

    For the Nuclear Regulatory Commission.

John A. Zwolinski,
Director, Division of Licensing Project Management, Office of Nuclear 
Reactor Regulation.
[FR Doc. 01-9953 Filed 4-20-01; 8:45 am]
BILLING CODE 7590-01-P