[Federal Register Volume 59, Number 190 (Monday, October 3, 1994)]
[Unknown Section]
[Page 0]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 94-24382]
[[Page Unknown]]
[Federal Register: October 3, 1994]
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NUCLEAR REGULATORY COMMISSION
Duke Power Company; Environmental Assessment and Finding of No
Significant Impact
[Docket Nos. 50-369 and 50-370]
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-9 and NPF-17, issued
to the Duke Power Company, licensee for the McGuire Nuclear Station
Units 1 and 2. The plants are located at the licensee's site in
Mecklenburg, County, North Carolina. The exemption was requested by the
licensee by letter dated June 28, 1994, and supplemented by letters
dated August 18, 1994 and September 7, 1994.
Environmental Assessment
Indentification of Proposed Action
The proposed action requests 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 the McGuire
Nuclear Station Units 1 and 2. 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,'' which 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.
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 Section III and XI of the ASME Code.
The Need for the Proposed Action
10 CFR 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 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.
10 CFR 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 on the
reactor vessel from exceeding the Appendix G P/T limits. To prevent
these valves 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 LTOP analysis indicates that
using the Appendix G safety margins to determine the PORV setpoint
would result in a pressure setpoint within its operating window, but
there would be no margin for normal operating pressure surges.
Therefore, operating with these limits could result in the lifting of
the PORVs and cavitation of the reactor coolant pumps during normal
operation. Therefore, the licensee proposed that in determining the
PORV setpoint for LTOP events for McGuire, 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. The alternate methodology is consistent with ASME Code
Case N-514. 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.
An exemption from 10 CFR 50.60 is required to use the alternate
methodology for calculating the maximum allowable pressure for LTOP
considerations. By application dated June 28, as supplemented August
18, 1994 (and further clarified by letter dated September 7, 1994), the
licensee requested an exemption from 10 CFR 50.60.
Environmental Impacts of the Proposed Action
The Commission has completed its evaluation of the licensee's
application.
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 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
percent 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, use of the proposed criteria will provide
adequate margins of safety to the reactor vessel during LTOP
transients.
Accordingly, the Commission concludes that this proposed action
would result in no significant radiological environmental impact.
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 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
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 Statements related to operation
of the McGuire Nuclear Station, dated April 1976, and its addendum
dated January 1981.
Agencies and Persons Consulted
The NRC staff consulted with the state of Tennessee regarding the
environmental impact of the proposed action. The state official had no
comments.
Finding of no Significant Impact
The Commission has determined not to prepare an environmental
impact statement for the proposed exemption.
Based upon the foregoing environmental assessment, the Commission
concludes that the proposed action will not have a significant effect
on the quality of the human environment.
For further details with respect to this action, see the request
for exemption dated June 28, as supplemented August 18, 1994 (and
further clarified by letter dated September 7, 1994), which is
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 Atkins Library, University of North
Carolina, Charlotte (UNCC Station), North Carolina 28223.
Dated at Rockville, Maryland, this 28th day of September, 1994.
For the Nuclear Regulatory Commission.
Victor Nerses,
Acting Project Director, Project Directorate II-3, Division of Reactor
Projects--I/II, Office of Nuclear Reactor Regulation.
[FR Doc. 94-24382 Filed 9-30-94; 8:45 am]
BILLING CODE 7590-01-M
