[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
