[Federal Register Volume 60, Number 103 (Tuesday, May 30, 1995)]
[Notices]
[Pages 28178-28180]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 95-13103]
=======================================================================
-----------------------------------------------------------------------
NUCLEAR REGULATORY COMMISSION
[Docket Nos. 50-424 and 50-425]
Georgia Power Company, et al; Vogtle Electric Generating Plant,
Units 1 and 2; Environmental Assessment and Finding of No Significant
Impact
The U.S. Nuclear Regulatory Commission (the Commission) is
considering issuance of an exemption from certain requirements of its
regulations to Facility Operating License Nos. NPF-68 and NPF-84,
issued to Georgia Power Company, et al. (the licensee) for operation of
the Vogtle Electric Generating Plant (Vogtle), Units 1 and 2, located
at the licensee's site in Burke County, Georgia.
Environmental Assessment
Identification of Proposed Action
The proposed action would grant an exemption from certain
requirements of 10 CFR 50.60, ``Acceptance Criteria for Fracture
Prevention Measures for Light-Water Nuclear Power Reactors for Normal
Operation,'' to allow application of an alternate methodology to
determine the low temperature overpressure protection (LTOP) setpoint
for Vogtle. The proposed alternate methodology is consistent with
guidelines developed by the American Society of Mechanical Engineers
(ASME) Working Group on Operating Plant Criteria (WGOPC) 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. These
guidelines have been incorporated into Code Case N-514, ``Low
Temperature Overpressure Protection,'' that 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 that will [[Page 28179]] endorse the 1993 Addenda and
Appendix G of Section XI into the regulations.
The philosophy used to develop Code Case N-514 guidelines is to
ensure that the LTOP limits are still below the pressure/temperature
(P/T) limits for normal operation, but allow the pressure that may
occur with activation of pressure-relieving devices to exceed the P/T
limits, provided acceptable margins are maintained during these events.
This philosophy protects the pressure vessel from LTOP events, and
still maintains the Technical Specification P/T limits applicable for
normal heatup and cooldown in accordance with Appendix G to 10 CFR Part
50 and Sections III and XI of the ASME Code.
The proposed action is in accordance with the licensee's
application for an exemption to 10 CFR 50.60 dated October 3, 1994, as
supplemented by letter dated March 1, 1995.
The Need for the Proposed Action
Section 50.60 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 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 transients that would produce pressure excursions
exceeding the Appendix G P/T limits while the reactor is operating at
low temperatures, the licensee installed an LTOP system. The LTOP
system includes pressure relieving devices in the form of Power-
Operated Relief Valves (PORVs) that are set at a pressure low enough
that if a transient occurred while the coolant temperature is below the
LTOP enabling temperature, they would prevent the pressure in the
reactor vessel from exceeding the Appendix G P/T limits. To prevent
these 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. Therefore, 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 Information
Notice 93-58. The new analysis accounts for the static head due to
elevation differences and the dynamic head effect of four reactor
coolant pumps (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 RCPs during normal operation.
The licensee proposed that in determining the PORV 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 required by Appendix G to 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 used
for LTOP. Code Case N-514, ``Low Temperature Overpressure Protection,''
has been approved by the ASME Code Committee. The content of his 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 letter dated October 3, 1994, as supplemented by letter
dated 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 50.60, the
licensee proposed an amendment to the Technical Specifications revising
the LTOP analysis. The new analysis removes the non-conservatism as
described previously. The amendment will be evaluated separate from
this exemption request.
Environmental Impacts of the Proposed Action
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 McGuire
reactor vessel material.
In determining the PORV setpoint for LTOP events, the licensee
proposed to use safety margins based on an alternative 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 requirements. This
results in a safety factor of 1.8 on the principal membrame 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, use of 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.
The change will not increase the probability or consequences of
accidents, no changes are being made in the type of any effluents that
may be released offsite, and there is no significant increase in the
allowable individual or cumulative occupational radiation exposure.
Accordingly, the Commission concludes that there are no significant
radiological environmental impacts associated with the proposed action.
With regard to potential non-radiological impacts, the proposed
change involves use of more realistic safety margins for determining
the PORV setpoint during LTOP events. It does not affect non-
radiological plant [[Page 28180]] effluents and has no other
environmental impact. Therefore, the Commission concludes that there
are no significant non-radiological environmental impacts associated
with the proposed exemption.
Alternative to the Proposed Action
Since the Commission has concluded there is no measurable
environmental impact associated with the proposed action, any
alternatives with equal or greater environmental impact need not be
evaluated. As an alternative to the proposed action, the staff
considered denial of the proposed action. Denial of the application
would result in no change in current environmental impacts. The
environmental impacts of the proposed action and the alternative action
are similar.
Alternative Use of Resources
This action did not involve the use of any resources not previously
considered in the Final Environmental Statement related to operation of
the Vogtle Electric Generating Plant.
Agencies and Persons Consulted
In accordance with its stated policy, on May 23, 1995, the staff
consulted with the Georgia State official, Mr. James L. Setser of the
Georgia Department of Natural Resources, regarding the environmental
impact of the proposed action. The state official had no comments.
Finding of No Significant Impact
Based upon the environmental assessment, the Commission concludes
that the proposed action will not have a significant effect on the
quality of the human environment. Accordingly, the Commission has
determined not to prepare an environmental impact statement for the
proposed action.
For further details with respect to this action, see the licensee's
letter dated October 3, 1994, as supplemented by letter dated March 1,
1995, which are available for public inspection at the Commission's
Public Document Room, 2120 L Street, NW., Washington, DC and at the
local public document room located at the Burke County Library, 412
Fourth Street, Waynesboro, Georgia 30830.
Dated at Rockville, Maryland, this 22nd day of May 1995.
For the Nuclear Regulatory Commission.
Herbert N. Berkow,
Director, Project Directorate II-2, Division of Reactor Projects--I/II
Office of Nuclear Reactor Regulation.
[FR Doc. 95-13103 Filed 5-26-95; 8:45 am]
BILLING CODE 7590-01-M
