[Federal Register Volume 66, Number 76 (Thursday, April 19, 2001)]
[Notices]
[Pages 20166-20167]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 01-9729]


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NUCLEAR REGULATORY COMMISSION

[Docket No. 50-293]


Entergy Nuclear Generation Company, Pilgrim Nuclear Power 
Station; Exemption

1.0  Background

    The Entergy Nuclear Generation Company (the licensee) is the holder 
of Facility Operating License No. DPR-35 which authorizes operation of 
the Pilgrim Nuclear Power Station. 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 
Plymouth County, Massachusetts.

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 that ``The appropriate requirements on both 
the pressure-temperature limits and the minimum permissible temperature 
must be met for all conditions.'' In addition, 10 CFR part 50, appendix 
G, 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 Kla fracture toughness curve 
in the determination of the P-T limits.
    By letter dated November 22, 2000, Entergy submitted a license 
amendment request to update the P-T limit curves for Pilgrim. By letter 
dated January 19, 2001, Entergy 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 
to 10 CFR part 50 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 ASME Code. Since the Pilgrim RPV is currently limited by lower 
shell-to-intermediate shell axial welds fabricated from material heat 
number 27204/12008, use of Code Case N-588 does not provide any benefit 
for Pilgrim. In a letter dated February 8, 2001, Entergy confirmed that 
the limiting reactor vessel welds are axial and withdrew its request 
for exemption for use of Code Case N-588.

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

[[Page 20167]]

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 or 
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)

    Entergy 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 to 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 Pilgrim RPV and reactor 
coolant pressure boundary (RCPB). Therefore, the staff concludes that 
Code Case N-640 is acceptable for application to the Pilgrim P-T 
limits.
    The staff has determined that Entergy has provided sufficient 
technical bases for using the methods of Code Case N-640 for the 
calculation of the P-T limits for the Pilgrim 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 Pilgrim 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 Entergy Nuclear Generation Company an 
exemption from the requirements of 10 CFR part 50, appendix G, for 
Pilgrim.
    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 18986).
    This exemption is effective upon issuance.

    Dated at Rockville, Maryland, this 13th 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. 01-9729 Filed 4-18-01; 8:45 am]
BILLING CODE 7590-01-P