[Federal Register Volume 66, Number 87 (Friday, May 4, 2001)]
[Notices]
[Pages 22619-22620]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 01-11277]


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NUCLEAR REGULATORY COMMISSION

[50-301]


Nuclear Management Company, LLC Duane Arnold Energy Center; 
Exemption

1.0  Background

    Nuclear Management Company, LLC (NMC, the licensee) is the holder 
of Facility Operating License No. DPR-49 which authorizes operation of 
the Duane Arnold Energy Center (DAEC). The license provides, among 
other things, that the facility is subject to all rules, regulations, 
and orders of the U.S. Nuclear Regulatory Commission (the Commission) 
now or hereafter in effect.
    The facility consists of a boiling water reactor located on NMC's 
DAEC site, which is located in Linn County, Iowa.

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.'' 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.
    To address provisions of the proposed amendments to the technical 
specification (TS) P-T limits, the licensee requested in its submittal 
dated October 16, 2000, that the staff exempt DAEC from application of 
specific requirements of 10 CFR part 50, Sec. 50.60(a) and 10 CFR part 
50, Appendix G, and substitute use of ASME Code Case N-640. Code Case 
N-640 permits the use of an alternate reference fracture toughness 
(K<INF>lc</INF> fracture toughness curve instead of K<INF>la</INF> 
fracture toughness curve) for reactor vessel materials in determining 
the P-T limits. The proposed action is in accordance with the 
licensee's application for exemption contained in the October 16, 2000, 
submittal, and is needed to support the TS amendment request that is 
contained in the same submittal. The proposed amendment will revise the 
P-T limits for heatup, cooldown, and inservice test limitations for the 
reactor coolant system (RCS) to 25 and 32 effective full power years 
(EFPYs).

Code Case N-640

    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 that the P-T limits meet the 
underlying intent of the Nuclear Regulatory Commission (NRC) 
regulations.
    The proposed amendment to revise the P-T limits for DAEC relies in 
part on the requested exemption. These revised P-T limits have been 
developed using the K<INF>lc</INF> fracture toughness curve shown in 
ASME Section XI, Appendix A, Figure A-2200-1, in lieu of the 
K<INF>la</INF> fracture toughness curve of ASME Section XI, Appendix G, 
Figure G-2210-1, as the lower bound for fracture toughness. The other 
margins involved with the ASME Section XI, Appendix G process of 
determining P-T limit curves remain unchanged.
    Use of the K<INF>lc</INF> curve in determining the lower bound 
fracture toughness in the development of P-T operating limits curve is 
more technically correct than the K<INF>la</INF> curve. The 
K<INF>lc</INF> curve appropriately implements the use of static 
initiation fracture toughness behavior to evaluate the controlled 
heatup and cooldown process of a reactor vessel. The licensee has 
determined that the use of the initial conservatism of the 
K<INF>la</INF> curve when the curve was codified in 1974 was justified. 
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 K<INF>la</INF> 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 
K<INF>lc</INF> 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. The operating window through which the 
operator heats up and cools down the RCS is determined by the 
difference between the maximum allowable pressure determined by 
Appendix G of ASME Section XI, and the minimum required pressure for 
the reactor coolant pump seals adjusted for instrument uncertainties.
    Since the RCS P-T operating window is defined by the P-T operating 
and test limit curves developed in accordance with the ASME Section XI, 
Appendix G procedure, continued operation of DAEC with these P-T curves 
without the relief provided by ASME Code Case N-640 may unnecessarily 
restrict the P-

[[Page 22620]]

T operating window, especially at low temperature conditions. The 
operating window becomes more restrictive with continued reactor vessel 
service. Implementation of the proposed P-T curves, as allowed by ASME 
Code Case N-640, does not significantly reduce the margin of safety. 
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 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, 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.

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. The staff accepts the 
licensee's determination that an exemption would be required to approve 
the use of Code Case N-640. The staff examined the licensee's rationale 
to support the exemption request and concurred that the use of the code 
case would also meet the underlying intent of these regulations. Based 
upon a consideration of the conservatism that is explicitly 
incorporated into the methodologies of 10 CFR part 50, Appendix G; 
Appendix G of the ASME Code; and regulatory guide (RG) 1.99, Revision 
2, the staff concluded that application of the code case as described 
would provide an adequate margin of safety against brittle failure of 
the RPV. This is also consistent with the determination that the staff 
has reached for other licensees under similar conditions based on the 
same considerations. Therefore, the staff concludes that requesting the 
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 the DAEC RCS.

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. Therefore, the Commission hereby grants NMC an 
exemption from the requirements of 10 CFR part 50, Sec. 50.60(a) and 10 
CFR part 50, Appendix G, for the DAEC.
    Pursuant to 10 CFR 51.32, an environmental assessment and finding 
of no significant impact has been prepared and published in the Federal 
Register (66 FR 20692). 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.

    Dated at Rockville, Maryland, this 27th day of April, 2001.

    For the Nuclear Regulatory Commission.
Cynthia A. Carpenter,
Acting Director, Division of Licensing Project Management, Office of 
Nuclear Reactor Regulation.
[FR Doc. 01-11277 Filed 5-3-01; 8:45 am]
BILLING CODE 7590-01-P