ML20078S814
| ML20078S814 | |
| Person / Time | |
|---|---|
| Site: | Palisades  |
| Issue date: | 02/21/1995 |
| From: | Hannon J Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20078S815 | List: |
| References | |
| NUDOCS 9502270228 | |
| Download: ML20078S814 (6) | |
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l 7590-01 UNITED STATES NUCLEAR REGULATORY COMMISSION l
CONSUMERS POWER COMPANY DOCKET NO. 50-255
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I PALISADES PLANT 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 No. DPR-20, issued to the Consumers Power Company, the licensee, for operation of the Palisades Nuclear Plant. The plant is located at the licensee's site in Van Buren County, Michigan.
ENVIRONM1NTAL ASSESSMENT Identification 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 Palisades Plant. 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 l
Code Case N-514, " Low Temperature Overpressure Protection," which has been 9502270228 950221 PDR ADOCK 05000255 p
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 philosophy used to develop Code Case N-514 guidelines is to ensure I
i that the LTOP limits are still below the pressure / temperature (P/T) limits for normal operation, but allows 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 t
pressure vessel from LTOP events and still maintains the Technical i
l 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.
i The proposed action is in accordance with the licensee's request for j
exemption dated February 10, 1995.
The Need for the Proposed Action:
l 30 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 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.
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 L10P 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 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 I
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 vsing the Appendix G safety margins to determine the PORV setpoint would result iii a pressure setpoint within its operating window, but there would be no margin for normal operating pressure surges. Therefore, operating with these ',imits 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 Palisades, 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
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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.
Environmental Imoacts 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 of the vessel wall thickness and a length of 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 Palisades 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% of the P/T limits of the existing ASME i
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 t
toughness, remain the same. Although this methodology would reduce the safety factor on the principal membrane stresses, use of the proposed criteria will v.
1 provide adequate margins of safety to the reactor vessel during LTOP transients.
. Because adequate safety margins will be maintained, the change will not increase the probability or consequences of accidents, no changes are being made in the types of any affluents 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 this proposed action would result in no significant radiological environmental impact.
With regard to potential nonradiological impacts, the proposed action involves use of more realistic safety margins for determining the PORV setpoint during LTOP events.
It does not affect nonradiological plant effluents and has no other environmental impact. Accordingly, the Commission concludes that there are no significant nonradiological 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. The principal alternative would be to deny the proposed action. Denial of the exemption would not reduce environmental impacts associated with the facility.
Alternative Use of Resources:
This action did not involve the use of any resources not previously i
considered in the Final Environmental Statement related to operation of the Palisades Plant, dated June 1972, and its addendum dated February 1978.
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" Acencies and Persons Consulted:
i In accordance with its stated policy, the staff consulted with the Michigan State official regarding the environmental impact of the proposed action. The State official had no comments.
FINDING OF NO SIGNIFICANT IMPACT I
Based upon the foregoing environmental assessment, the Consission I
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 request for exemption dated February 10, 1995, which is available for public inspection at the Commission's Public Document Room, The Gelman Building, 2120 L Street, NW., Washington, DC and at the local public document room located at the Van Wylen Library, Hope College, Holland, MI 49423.
Dated at Rockville, Maryland, this 21st day of February,1995.
FOR THE NUCLEAR REGULATORY COMMISSION
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John N. Hannon, Director Project Directorate 111-1 Division of Reactor Projects - III/IV Office of Nuclear Reactor Regulation i
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