[Federal Register Volume 65, Number 221 (Wednesday, November 15, 2000)]
[Notices]
[Pages 69052-69053]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 00-29249]


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NUCLEAR REGULATORY COMMISSION

[Docket Nos. 50-373, 50-374]


In the Matter of Commonwealth Edison Company (LaSalle County 
Station, Units 1 and 2); Exemption

I.

    Commonwealth Edison Company (ComEd, the licensee) is the holder of 
Facility Operating Licenses Nos. NPF-11 and NPF-18 for operation of 
LaSalle County Station, Units 1 and 2, located in LaSalle County, 
Illinois. The licenses state, among other things, that the facility is 
subject to all of the rules, regulations, and orders of the U.S. 
Nuclear Regulatory Commission (the Commission) now or hereafter in 
effect.

II.

    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 P-T limits must meet the safety margin requirements 
specified in the American Society of Mechanical Engineers (ASME) Boiler 
and Pressure Vessel Code (Code), Section XI, Appendix G. ASME Code 
specifies use of K1A fracture toughness curve.
    To address provisions of the proposed amendments to the technical 
specification (TS) P-T limits, in its submittal of February 29, 2000, 
the licensee requested that the staff exempt LaSalle from application 
of specific requirements of 10 CFR 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 (K1c fracture toughness curve instead of 
K1a fracture toughness curve) for reactor vessel materials 
in determining the P-T limits. Since the K1c fracture 
toughness curve shown in ASME Code, Section XI, Appendix A, Figure A-
2200-1 provides greater allowable fracture toughness than the 
corresponding K1a fracture toughness curve of ASME Code, 
Section XI, Appendix G, Figure G-2210-1 (the K1a fracture 
toughness 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 be required.

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

    The licensee has proposed an exemption to allow the use of ASME 
Code Case N-640 in conjunction with ASME Code, Section XI; 10 CFR 
50.60(a); and 10 CFR Part 50, Appendix G, to determine P-T limits.
    The proposed amendments to revise the P-T limits for LaSalle rely 
in part on the requested exemption. These revised P-T limits have been 
developed using the K1c fracture toughness curve, in lieu of 
the K1a fracture toughness curve, as the lower bound for 
fracture toughness.
    Use of the K1c 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 K1a 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 
K1c 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 initial conservatism of the K1a 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 K1a 
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 K1c curve would enhance overall plant 
safety by opening the P-T operating window with the greatest safety 
benefit in the region of low temperature operations.
    Since the reactor coolant system (RCS) 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, continued 
operation of LaSalle with these P-T curves without the relief provided 
by ASME Code Case N-640 would unnecessarily require that the RPV 
maintain a temperature exceeding 212 degrees Fahrenheit in a limited 
operating window during pressure tests. Consequently, steam vapor 
hazards would continue to be one of the safety concerns for personnel 
conducting inspections in primary containment. Implementation of the 
proposed P-T curves, as allowed by ASME Code Case N-640, does not 
significantly reduce the margin of safety and would eliminate steam 
vapor hazards by allowing inspections in primary containment to be 
conducted at lower coolant temperature. Thus, pursuant to 10 CFR 
50.12(a)(2)(ii), the underlying purpose of the regulation will continue 
to be served.
    In summary, the ASME Code, 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

[[Page 69053]]

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 Code, Section XI, Appendix G, requirements by 
application of ASME Code Case N-640, while maintaining, pursuant to 10 
CFR 50.12(a)(2)(ii), the underlying purpose of the ASME Code and the 
NRC regulations to ensure an acceptable margin of safety.

III.

    Pursuant to 10 CFR 50.12(a), 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. . . .''
    The underlying purpose of the requirement to use the K1a 
curve to develop P-T limits is to provide an adequate margin of safety 
against brittle failure of the RPV. Code Case N-640 permits application 
of the lower bound static initiation fracture toughness value 
(K1a) equation as the basis for establishing the curves in 
lieu of using the lower bound crack arrest fracture toughness value 
equation (i.e., the K1a 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 K1c 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 K1a 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 
K1c equation appropriately implements the use of the static 
initiation fracture toughness behavior to evaluate the controlled 
heatup and cooldown process of a reactor vessel. Therefore, use of the 
K1c curve in developing P-T limits provides an adequate 
margin against brittle failure of the RPV. As a result, the application 
of the regulation in the particular circumstances is not necessary to 
achieve the underlying purpose of the rule.
    Therefore, the staff concludes that requesting 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 LaSalle County Station, Units 1 and 2.

IV.

    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, and that special circumstances are present. Therefore, 
the Commission hereby grants Commonwealth Edison Company an exemption 
from the requirements of 10 CFR 50.60(a) and 10 CFR Part 50, Appendix 
G, for LaSalle County Station, Units 1 and 2.
    Pursuant to 10 CFR 51.32, an environmental assessment and finding 
of no significant impact has been prepared and published in the Federal 
Register (65 FR 60986). Accordingly, based upon the environmental 
assessment, the Commission has determined that the granting of this 
exemption will not result in any significant effect on the quality of 
the human environment.
    This exemption is effective upon issuance.


    For the Nuclear Regulatory Commission.
    Dated at Rockville, Maryland, this 8th day of November 2000.
John A. Zwolinski,
Director, Division of Licensing Project Management, Office of Nuclear 
Reactor Regulation.
[FR Doc. 00-29249 Filed 11-14-00; 8:45 am]
BILLING CODE 7590-01-P