[Federal Register Volume 66, Number 43 (Monday, March 5, 2001)]
[Notices]
[Pages 13353-13354]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 01-5217]


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NUCLEAR REGULATORY COMMISSION

[Docket Nos. 50-317 and 50-318]


Calvert Cliffs Nuclear Power Plant, Inc; Calvert Cliffs Nuclear 
Power Plant, Unit Nos. 1 and 2; Exemption

1.0  Backround

    Calvert Cliffs Nuclear Power Plant, Inc. (CCNPPI, the licensee) is 
the holder of Renewed Facility Operating License Nos. DPR-53 and DPR-69 
which authorize operation of the Calvert Cliffs Nuclear Power Plant, 
Unit Nos. 1 and 2 (CCNPP). 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 
Calvert County, Maryland.

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) for 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 also 
states that the ``P-T limits identified as ``ASME [American Society of 
Mechanical Engineers] Appendix G limits'' in Table 1 require that the 
limits must be at least as conservative as limits obtained by

[[Page 13354]]

following the methods of analysis and the margins of safety of Appendix 
G of Section XI of the ASME Code.'' Section XI of the ASME Code, 
Appendix G, Figure G-2210-1 specifies a Kla fracture 
toughness curve for reactor vessel materials in determining P-T limits.
    To address provisions of a proposed license amendment to the 
Technical Specification P-T limits for CCNPP, the licensee requested, 
in its submittal of September 14, 2000, that the NRC staff exempt CCNPP 
from application of specific requirements of 10 CFR Part 50, Section 
50.60(a) and Appendix G, and substitute use of ASME Code Case N-640. 
Code Case N-640 permits the use of an alternate reference fracture 
toughness (Klc fracture toughness curve instead of 
Kla fracture toughness curve) for reactor vessel materials 
in determining the P-T limits. Since the Klc fracture 
toughness curve shown in ASME Section XI, Appendix A, Figure A-2200-1 
(the Klc fracture toughness curve, Klc curve) 
provides greater allowable fracture toughness than the corresponding 
Kla fracture toughness curve of ASME Section XI, Appendix G, 
Figure G-2210-1 (the Kla fracture toughness curve, 
Kla curve), using Code Case N-640 for establishing the P-T 
limits 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 also be required by 10 CFR 50.60.

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

    The licensee has proposed an exemption to allow use of ASME Code 
Case N-640 in conjunction with ASME Section XI, 10 CFR 50.60(a) and 10 
CFR part 50, Appendix G, to determine P-T limits. These revised P-T 
limits have been developed using the Klc fracture toughness 
curve, in lieu of the Kla fracture toughness curve, as the 
lower bound for fracture toughness.
    Use of the Klc curve in determining the lower bound 
fracture toughness in the development of P-T operating limits curve is 
more technically correct than use of the Kla 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 
Klc curve appropriately implements the use of static 
initiation fracture toughness behavior to evaluate the controlled 
heatup and cooldown process of a reactor vessel. The NRC staff has 
required use of the initial conservatism of the Kla curve 
since 1974 when the curve was codified. This initial conservatism was 
necessary due to the limited knowledge of RPV materials. Since 1974, 
additional knowledge has been gained about RPV materials which 
demonstrates that the lower bound on fracture toughness provided by the 
Kla curve is well beyond the margin of safety required to 
protect the public health and safety from potential RPV failure. In 
addition, P-T curves based on the Klc 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.

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. These circumstances include 
the special circumstances that ``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; 
* * * ''
    The underlying purpose of 10 CFR part 50, Appendix G is to provide 
an adequate margin of safety against brittle failure of the RPV. Use of 
a P-T limit that is at least as conservative as the limits obtained by 
following the methods of analysis and margin of safety of the ASME 
Code, Section XI, Appendix G is not necessary, in this case, to achieve 
the underlying purpose of the rule. Specifically, substitution of the 
Klc fracture toughness curve for the Kla fracture 
toughness curve for establishing the P-T limits provides a more 
technically correct outcome in that it accounts for the rate of loading 
during heatup or cooldown and is more representative of a static 
condition. In addition, the staff has determined that improved 
knowledge regarding the RPV materials justifies elimination of 
unnecessary conservatisms, such as that brought about by the use of the 
Kla curve. Use of the less conservative Klc curve 
would provide an adequate margin of safety against brittle failure of 
the RPV in this case, due in part to the remaining conservatisms 
incorporated into the methodologies of 10 CFR part 50, Appendix G and 
Regulatory Guide 1.99 which would still be applicable. Therefore, use 
of a P-T limit that is at least as conservative as the limits obtained 
by following the methods and margins of safety of the ASME Code, 
Section XI, Appendix G, is not necessary in this case to achieve the 
underlying purpose of the rule, i.e., to provide sufficient margin of 
RPV fracture toughness to ensure structural integrity of the RPV.
    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 methodology of Code Case N-640 may be used to revise the P-T limits 
for CCNPP.

4.0  Conclusion

    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 NRC staff concurs that this increased knowledge permits 
relaxation of the ASME Section XI, Appendix G, requirements by 
application of ASME Code Case N-640. Implementation of the proposed P-T 
limits, as allowed by ASME Code Case N-640, are sufficient to ensure 
the structural integrity of RPVs during plant operations. Thus, 
pursuant to 10 CFR 50.12(a)(2)(ii), the underlying purpose of the 
regulation will continue to be served.
    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 in that 
application of the regulation is not necessary to achieve the 
underlying purpose of the rule. Therefore, the Commission hereby grants 
CCNPPI an exemption from the requirements of 10 CFR Part 50, Section 
50.60(a) and 10 CFR Part 50, Appendix G, for CCNPP.
    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 9729).
    This exemption is effective upon issuance.

    Dated at Rockville, Maryland, this 26th day of February 2001.

John A. Zwolinski,
 Director, Division of Licensing Project Management, Office of Nuclear 
Reactor Regulation.
[FR Doc. 01-5217 Filed 3-2-01; 8:45 am]
BILLING CODE 7590-01-P