[Federal Register Volume 60, Number 112 (Monday, June 12, 1995)]
[Notices]
[Pages 30903-30904]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 95-14299]



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NUCLEAR REGULATORY COMMISSION
[Docket Nos. 50-424 and 50-425]


Georgia Power Company, Et Al.; (Vogtle Electric Generating Plant, 
Units 1 and 2)

Exemption

I

    Georgia Power Company, et al. (the licensee) is the holder of 
Facility Operating License Nos. NPR-68 and NPF-81, which authorize 
operation of the Vogtle Electric Generating Plant (VEGP), Units 1 and 
2, respectively. The licenses provide, among other things, that the 
licensee is subject to all rules, regulations, and orders of the 
Commission now or hereafter in effect.
    The facilities consist of two pressurized water reactors, VEGP 
Units 1 and 2, at the licensee's site located near Waynesboro, Georgia.

II

    Title 10 of the Code of Federal Regulations (10 CFR), Sec. 50.60, 
``Acceptance Criteria for Fracture Prevention Measures for Light-Water 
Nuclear Power Reactors for Normal Operation,'' states that all light-
water nuclear power reactors must meet the fracture toughness and 
material surveillance program requirements for the reactor coolant 
pressure boundary as set forth in Appendices G and H to 10 CFR part 50. 
Appendix G to 10 CFR part 50 defines pressure/temperature (P/T) limits 
during any condition of normal operation, including anticipated 
operational occurrences and system hydrostatic tests to which the 
pressure boundary may be subjected over its service lifetime. Section 
50.60 (b) specifies that alternatives to the described requirements in 
Appendices G and H to 10 CFR part 50 may be used when an exemption is 
granted by the Commission under 10 CFR 50.12.
    To prevent low temperature overpressure transients that would 
produce pressure excursions exceeding the Appendix G P/T limits while 
the reactor is operating at low temperatures, the licensee installed a 
low temperature overpressure (LTOP) system. The system includes 
pressure-relieving devices called Power-Operated Relief Valves (PORVs). 
The PORVs are set at a pressure low enough so that if an LTOP transient 
occurred, the mitigation system would prevent the pressure in the 
reactor vessel from exceeding the Appendix G P/T limits. To prevent the 
PORVs from lifting as a result of normal operating pressure surges 
(e.g., reactor coolant pump starting, and shifting operating charging 
pumps) with the reactor coolant system in a water solid condition, the 
operating pressure must be maintained below the PORV setpoint. In 
addition, in order to prevent cavitation of a reactor coolant pump, the 
operator must maintain a differential pressure across the reactor 
coolant pump seals. Hence, the licensee must operate the plant in a 
pressure window that is defined as the difference between the minimum 
required pressure to start a reactor coolant pump and the operating 
margin to prevent lifting of the PORVs due to normal operating pressure 
surges. The licensee's proposed LTOP analysis includes changes to 
account for the non-conservatism identified in Westinghouse Nuclear 
Safety Advisory Letter 93005A and NRC Information Notice 93-58. The new 
analysis accounts for the static head due to evaluation differences and 
the dynamic head effect of four reactor coolant pump (RCP) operation. 
By including these factors and using the Appendix G safety margins, the 
licensee determined that the operating margin to the PORV setpoint 
would be depleted at approximately 120  deg.F for Unit 1 and 145  deg.F 
for Unit 2. Therefore, operating with these limits could result in the 
lifting of the PORVs and cavitation of the reactor coolant pumps during 
normal operation.
    The licensee proposed that in determining the design setpoint for 
LTOP events for Vogtle Units 1 and 2, the allowable pressure be 
determined using the safety margins developed in an alternate 
methodology in lieu of the safety margins currently required by 
Appendix G, 10 CFR part 50. Designated Code Case N-514, the proposed 
alternate methodology is consistent with guidelines developed by the 
American Society of Mechanical Engineers (ASME) Working Group on 
Operating Plant Criteria to define pressure limits during LTOP events 
that avoid certain unnecessary operational restrictions, provide 
adequate margins against failure of the reactor pressure vessel, and 
reduce the potential for unnecessary activation of pressure-relieving 
devices [[Page 30904]] used for LTOP. Code Case N-514, ``Low 
Temperature Overpressure Protection,'' has been approved by the ASME 
Code Committee. The content of this Code case has been incorporated 
into Appendix G of Section XI of the ASME Code and Published in the 
1993 Addenda to Section XI. The NRC staff is revising 10 CFR 50.55a, 
which will endorse the 1993 Addenda and Appendix G of Section XI into 
the regulations.
    An exemption from 10 CFR 50.60 is required to use the alternate 
methodology for calculating the maximum allowable pressure for the LTOP 
setpoint. By application dated October 3, 1994, as supplemented March 
1, 1995, the licensee requested an exemption from 10 CFR 50.60 for this 
purpose.
    In addition to requesting the exemption from 10 CFR 50.50, the 
licensee proposed an amendment to the Technical Specifications revising 
the LTOP analysis. The new analysis removes the non-conservatism as 
described previously.
III

    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. 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 10 CFR 50.60 Appendix G is to establish 
fracture toughness requirements for ferritic materials of pressure-
retaining components of the reactor coolant pressure boundary to 
provide adequate margins of safety during any condition of normal 
operation, including anticipated operational occurrences, to which the 
pressure boundary may be subjected over its service lifetime. Section 
IV.A.2 of this appendix requires that the reactor vessel be operated 
with P/T limits at least as conservative as those obtained by following 
the methods of analysis and the required margins of safety of Appendix 
G of the ASME Code.
    Appendix G of the ASME Code requires that the P/T limits be 
calculated: (a) Using a safety factor of 2 on the principal membrane 
(pressure) stresses, (b) assuming a flaw at the surface with a depth of 
one-quarter (1/4) of the vessel wall thickness and a length of six (6) 
times its depth, and (c) using a conservative fracture toughness curve 
that is based on the lower bound of static, dynamic, and crack arrest 
fracture toughness tests on material similar to the Vogtle reactor 
vessel material.
    In determining the setpoint for LTOP events, the licensee proposed 
to use safety margins based on an alternate methodology consistent with 
the proposed ASME Code Case N-514 guidelines. The ASME Code Case N-514 
allows determination of the setpoint for LTOP events such that the 
maximum pressure in the vessel would not exceed 110% of the P/T limits 
of the existing ASME Appendix G. This results in a safety factor of 1.8 
on the principal membrane stresses. All other factors, including 
assumed flaw size and fracture toughness, remain the same. Although 
this methodology would reduce the safety factor on the principal 
membrane stresses, the proposed criteria will provide adequate margins 
of safety to the reactor vessel during LTOP transients and will satisfy 
the underlying purpose of 10 CFR 50.60 for fracture toughness 
requirements.
    Using the licensee's proposed safety factors instead of Appendix G 
safety factors to calculate the LTOP setpoint will permit a higher LTOP 
setpoint than would otherwise be required and will provide added margin 
to prevent normal operating surges from lifting the PORVs or cavitation 
of the reactor coolant pumps.

IV

    For the foregoing reasons, the NRC staff has concluded that the 
licensee's proposed use of the alternate methodology in determining the 
acceptable setpoint for LTOP events will not present an undue risk to 
public health and safety and is consistent with the common defense and 
security. The NRC staff has determined that there are special 
circumstances present, as specified in 10 CFR 50.12(a)(2), such that 
application of 10 CFR 50.60 is not necessary in order to achieve the 
underlying purpose of this regulation.
    Accordingly, the Commission has determined that, pursuant to 10 CFR 
50.12(a), this 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 the licensee 
an exemption from the requirements of 10 CFR 50.60 such that in 
determining the setpoint for LTOP events, the Appendix G curves for P/T 
limits are not exceeded by more than 10 percent in order to be in 
compliance with these regulations. This exemption is applicable only to 
LTOP conditions during normal operation.
    Pursuant to 10 CFR 51.32, the Commission has determined that the 
granting of this exemption will not result in any significant adverse 
environmental impact (60 FR 28178).
    This exemption is effective upon issuance.

    Dated at Rockville, Maryland, this 5th day of June 1995.

    For the Nuclear Regulatory Commission.
Steven A. Varga,
Director, Division of Reactor Projects--I/II, Office of Nuclear Reactor 
Regulation.
[FR Doc. 95-14299 Filed 6-9-95; 8:45 am]
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