[Federal Register Volume 63, Number 64 (Friday, April 3, 1998)]
[Notices]
[Pages 16591-16592]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 98-8770]


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NUCLEAR REGULATORY COMMISSION

[Docket No. 50-483]


In the Matter of Union Electric Company (Callaway Plant, Unit 1); 
Exemption

I

    Union Electric Company (UE or the licensee) is the holder of 
Facility Operating License No. NPF-30, which authorizes operation of 
the Callaway Plant, Unit 1. The license provides, among other things, 
that the licensee is subject to all rules, regulations, and orders of 
the Commission now and hereafter in effect.
    The facility is a pressurized water reactor located at the 
licensee's site in Callaway County, Missouri.

II

    Section 50.60(a) to 10 CFR Part 50 requires that, except as 
provided in Section 50.60(b), all light-water nuclear power reactors, 
other than reactor facilities for which the certifications required 
under Section 50.82(a)(1) have been submitted, must meet the fracture 
toughness and material surveillance program requirements for the 
reactor coolant pressure boundary set forth in Appendices G and H of 10 
CFR Part 50. Section 50.60(b) of 10 CFR Part 50 states that proposed 
alternatives to the described requirements of Appendices G and H of 
Part 50 or portions thereof may be used when an exemption is granted by 
the Commission under 10 CFR 50.12.

III

    By letter dated August 22, 1997, Union Electric Company requested 
that the NRC exempt the Callaway Plant, Unit 1 from the application of 
specific requirements of 10 CFR 50.60 and Appendix G to 10 CFR Part 50. 
Specifically, Union Electric proposes to use American Society for 
Mechanical Engineers (ASME) Code Case N-514 to permit setting the 
pressure setpoint of Callaway's cold overpressure mitigation system 
(COMS) such that the pressure-temperature (P-T) limits required by 
Appendix G of 10 CFR Part 50 could be exceeded by ten percent during a 
low temperature pressure transient.
    The Commission has established requirements in 10 CFR Part 50 to 
protect the integrity of the reactor coolant system pressure boundary. 
As a part of these, Appendix G of 10 CFR Part 50 requires that P-T 
limits be established for reactor pressure vessels (RPVs) during normal 
operation and vessel hydrostatic testing. As stated in Appendix G, 
``The appropriate requirements on * * * the pressure-temperature limits 
* * * must be met for all conditions.'' In order to avoid approaching 
these P-T limit curves and provide pressure relief during low 
temperature overpressurization events, pressurized water reactor 
licensees have installed protection systems (COMS/LTOPS) as part of the 
reactor coolant system pressure boundary. Union Electric is required as 
part of the Callaway Plant Technical Specifications (TS) to develop, 
update, and submit reactor vessel P-T limits and COMS setpoints for NRC 
review and approval.
    Union Electric determined that the exemption request from the 
provisions of 10 CFR 50.60 and Appendix G was necessary since these 
regulations require, as noted above, that reactor vessel conditions not 
exceed the P-T limits established by Appendix G. In referring to 10 CFR 
50.12 on specific exemptions, Union Electric cited special 
circumstances regarding achievement of the underlying purpose of the 
regulation as their basis for requesting this exemption [10 CFR 
50.12(a)(2)(ii)].
    Union Electric noted in support of the 10 CFR 50.12(a)(2)(ii) 
criteria that the underlying purpose of the subject regulation is to 
establish limits to protect the reactor vessel from brittle failure 
during low temperature operation and that the COMS provides a physical 
means of assuring operation remains within these limits. Union Electric 
proposed that establishing the COMS pressure setpoint in accordance 
with the N-514 provisions, such that the vessel pressure would not 
exceed 110 percent of the P-T limit allowables, would still provide an 
acceptable level of safety and mitigate the potential for an 
inadvertent actuation of the COMS. The use of N-514 was based on the 
conservatisms which have been explicitly incorporated into the 
procedure for developing the P-T limit curves. This procedure, 
referenced from Appendix G to Section XI of the ASME Code, includes the 
following conservatisms: (1) A safety factor of 2 on the pressure 
stresses; (2) a margin factor applied to RTNDT using 
Regulatory Guide 1.99, Revision 2, ``Radiation Embrittlement of Reactor 
Vessel Materials;'' (3) an assumed \1/4\T flaw with a 6:1 aspect ratio; 
and (4) a limiting material toughness based on dynamic and crack arrest 
data.
    In addition, Union Electric stated that a COMS pressure setpoint 
should ``also be high enough to prevent the inadvertent actuation of 
the COMS as a result of normal operating pressure surges. Application 
of the various instrument and calculational uncertainties has resulted 
in a COMS actuation setpoint that established an operating window that 
is too narrow to permit reasonable system makeup and pressure 
control.'' Such an inadvertent actuation could lead to the unnecessary 
release of reactor coolant inside containment and could introduce 
undesirable thermal transients in the RCS.
    The Commission has determined that application of 10 CFR 50.60 in 
these particular circumstances is not

[[Page 16592]]

necessary to achieve the underlying purpose of that rule and that the 
use of Code Case N-514 would meet the underlying intent of the 
regulation. Based upon a consideration of the conservatisms which are 
explicitly defined in the Appendix G methodology, it was concluded that 
permitting the COMS setpoint to be established such that the vessel 
pressure would not exceed 110 percent of the limit defined by the P-T 
limit curves would provide an adequate margin of safety against brittle 
failure of the reactor vessel. This is also consistent with the 
determination that has been reached for other licensees under similar 
conditions based on the same considerations. Therefore, the exemption 
requested under the special circumstances of 10 CFR 50.12(a)(2)(ii) was 
found to be acceptable. The staff also agrees that limiting the 
potential for inadvertent COMS actuation may improve plant safety.

IV

    The Commission has determined that, pursuant to 10 CFR 50.12, this 
exemption is authorized by law, will not present an undue risk to the 
public health and safety, is consistent with the common defense and 
security, and is otherwise in the public interest. Therefore, the 
Commission hereby grants Union Electric Company an exemption from the 
requirements of 10 CFR 50.60 in order to apply ASME Code Case N-514 for 
determining the Callaway plant's cold overpressurization mitigation 
system pressure setpoint.
    Pursuant to 10 CFR 51.32, the Commission has determined that the 
granting of this exemption will have no significant impact on the 
environment (63 FR 14739).
    This exemption is effective upon issuance.

    Dated at Rockville, Maryland this 30th day of March 1998.

    For the Nuclear Regulatory Commission.
Samuel J. Collins,
Director, Office of Nuclear Reactor Regulation.
[FR Doc. 98-8770 Filed 4-2-98; 8:45 am]
BILLING CODE 7590-01-P