[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