[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]
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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