[Federal Register Volume 60, Number 215 (Tuesday, November 7, 1995)]
[Notices]
[Pages 56178-56179]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 95-27512]



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NUCLEAR REGULATORY COMMISSION
[Docket Nos. 50-280 and 50-281]


Virginia Electric and Power Company (Surry Power Station Units 1 
and 2); Exemption

I
    The Virginia Electric and Power Company (the licensee) is the 
holder of Facility Operating License Nos. DPR-32 and DPR-37, which 
authorize operation of the Surry Power Station, 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, Surry 
Power Station, Units 1 and 2, at the licensee's site located in Surry 
County, Virginia.
II
    In its letter dated June 8, 1995, the licensee requested an 
exemption from the Commission's regulations. Title 10 of the Code of 
Federal Regulations, Part 50, Section 60 (10 CFR 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. It is specified in 10 CFR 
50.60(b) 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.
    The licensee has requested the use of Code Case N-514, ``Low 
Temperature Overpressure Protection,'' which allows exceedance of the 
Appendix G safety limits by 10%. 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 used for LTOP. Code Case N-514 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. In order to utilize Code Case N-514 and to 
permit LTOP events to exceed the Appendix G safety limits, the licensee 
has requested an exemption to 10 CFR 50.60 in a letter dated June 8, 
1995.
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 


[[Page 56179]]
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 Surry 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, thus, will 
satisfy the underlying purpose of 10 CFR 50.60 for fracture toughness 
requirements. Further, by relieving the operational restrictions, the 
potential for undesirable lifting of the PORV would be reduced, thereby 
improving plant safety.
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), in 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), an 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 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 have a significant effect on the 
quality of the human environment (60 FR 54710).
    This exemption is effective upon issuance.

    Dated at Rockville, Maryland, this 31st day of October 1995.

    For the Nuclear Regulatory Commission.
Steven A. Varga,
Director, Division of Reactor Projects--I/II, Office of Nuclear Reactor 
Regulation.
[FR Doc. 95-27512 Filed 11-6-95; 8:45 am]
BILLING CODE 7590-01-P