ML20054K058
| ML20054K058 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 06/23/1982 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20054K056 | List: |
| References | |
| NUDOCS 8206300357 | |
| Download: ML20054K058 (6) | |
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ENCLOSURE 1 ie-SAFETY EVALU'ATION MILLSTONE NUCLEAR POWER STATION, UNIT 1 DOCKET NO. 50-245 DEGRADED GRID VOLTAGE PROTECTION FOR THE CLASS lE SYSTEM INTRODUCTION ~AND
SUMMARY
The criteria and staff positions pertaining to degraded' grid voltage protection were transmitted to Northeast Nuclear Energy Company (NNECo) by NRC Generic
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Letter dated June 3, 1977.
I6 N sponss to this, by letters dated August 1, 1977, August 10,1979, April 29,1980, July,16,1980~, August 20,- 1980, April 21,1982 and drawingsinformally provided to the LPM J. Shea on May 15,1982, the licensee proposed certain design modifications to the degraded grid voltage protective system for Millstone Unit 1.
A detailed review and technical evaluation of the proposed modifications was performed by LLL, under contract to the NRC, and with general supervision by NRC staff. This work is reported by LLL in " Degraded Grid Protection for Class lE Power System Millstone Nuclear Power Station, Unit 1.
We have reviewed the technical evaluation report and the licensee submittals and find that additional information is still required to complete the review of this issue.
EVALUATION CRITERIA, The criteria used by LLL in its technical evaluation of the proposed changes include GDC-17 (" Electric Power Systems") of Appendix A to 10 CFR 50 U IEEE Standard 279-1971 (" Criteria for Protection Systems for Nuclear ' Power
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Generating Stations"); IEEE Standard 308-1977 (" Voltage Ratings for Electrical Power Systems and Equipment - 60 Hz"); and staff positions i
defined in NRC Generic Letter to NNECo dated June 3, 1977.
8206300357 820623 PDR ADOCK 05000245 P
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PROPOSED CHANGES, MODIFICATIONS AND DISCUSSION The licensee has propcsed to relocate the first level (loss'of voltage) and second level (degraded grid voltage) relays, prescatly connected to the bushing potential devices, to the 4160 volt Class lE buses.
Discussions with the licensee indicates that the first and second level relays relocation will be accomplished during the refuel'ng outage presently scheduled for the fall of 1982. The second level undervoltage relays will be placed in
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operation at that time. However; due to anticipated delays in completing the design and procurement of equipment for the'first level loss of power protection relays, that portion of the system will not be placed in operation until the refueling outage presently scheduled for the summer of 1984. This is acceptable to the staff.
The proposed modifications for the second level undervoltage protection system retains the feature that will permit automatte separation of the Class lE power system from offsite power only if a degraded grid exists coincident with a safety injection signal (LOCA). This approach provides protection to the Class lE equipment needed to mitigate the consequences of an accident and is acceptable.
For a degraded grid condition without a LOCA an alarm will be actuated and operator action will be taken to restore the grid to an acceptable level.
In the event nperator action is not successful in restoring grid voltage within an acceptable time period, the operator will manually start the ensite diesel / gas turbine generator and separate the Class lE buses from the offsite power system. The Class lE loads would then be sequenced onto the onsite emergency generators. This
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approach deviates from the staff position that requires automatic isolation of the offsite power system from such undervoltage after a time delay.
Acceptability of this alternate approach requires demonstration by the licensee that adequate safety systems will be available for safe shutdown of the reactor for these conditions and that appropriate plant operat'ing procedures are developed and available to the operator for the required manual operator action. We recommend that these procedures be considered as an unresolved issue in the integrated assessment of Millstone 1.
In response to the above concerns, the licensee in a submittal dated April 21, 1982 p'rovided a list of systems, that will not be exposed to degraded grid voltage, which would be available to bring the plant to a safe shutdown under non-LOCA conditions. The staff has reviewed this listing and concurs with the licensee's approach with one exception.
This exception being the completion of modifications in the isolation condenser system such that the available systems will provide redundant capability to shut down the plant and maintain it at safe shutdown under non-LOCA conditions. The modifications consist of replacing one AC motor operated valve (MOV) on the cooling water side of the isolation condenser heat exchanger with a DC MOV and changing the AC motor for the condensate transfer pump, to a DC motor. Upon completion of these modifications this j
system will be independent from AC power. The licensee has committed to i
perform these modifications during the refueling outage presently scheduled for the fall of 1982. A rdundant means of providing safe shutdown is j
provided by the Automatic Depressurization System (ADS), which uses air operated valves, with backup bottled air supply, to depressurize the system and allow placing the Low Pressure Coolant Injection (LPCI) and Core Spray (CS) system (s) in operation.
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4-On the basis of the above and that protection devices i.e., circuit breakers fuses, relays,...etc., are provided to prevent damage to the equipment required for plant safe shutdown and that an alarm is installed to alert the operator to this abnormal condition, we find the licensee's alternate approach for manual operator action under degraded grid condition without an accident acceptable. Acceptability of this approach is subject to completion of the modifications on the isolation condenser and
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institution of adequate procedures covering actions to be taken by the
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operator during a degraded grid under non-accident conditions.
In addition, we require the following information on the proposed undervoltage protection relaying system:
1.
Details on how the load shedding featu a will be bypassed and how
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reinstatement of load shedding and load sequencing on a emergency generator breaker trip will be a,ccomplished.
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Design details and a description of operation of the first level less of power undervoltage relaying system.
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Technical Specifications to cover relay setpoints and tolerances, limiting conditions for operation, and surveillance testing for the undervoltage relaying system.
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A schedule for completion of all modifications on the first level l'
(loss of power) and second level (degraded grid voltage) protective relaying systems by the completion of the refueling outage scheduled for the. fall of 1982.
C0flCLUSIOf15 We have reviewed the licensee submittals and the Lt.L technical-evaluation
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report and find that:
1.
Tile existing undervoltage protection system does not meet the total requirements of the staff's position. The licensee has conrnitted to relocate the undervoltage protective relays to the Class lE buses.
The design will provide automatic separation of the Class lE buses from a degraded offsite power source under accident conditions.
This aspect meets the staff's position, protects the Cla'ss lE equipment from degraded voltage, and is acceptable.
2.
The licensee's proposal to use operator action instead of automatic disconnection of the Class lE buses from a degraded offsite power source under non-accident conditions does not meet the staffs position. To justify this alternate approach, the lic'ensee has shown that redundant safety systems, which are not exposed to degraded voltage, are available to maintain the plant in a safe shutdown condition. The staff has reviewed the licensee's proposal and finds that upon completion of the modifications on the isolation condenser system as previously stated, these systems will be available to affect a safe plant shutdown under non-accident conditions. Based on the above,we find the licensee alternate
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-G-2.1 approach acceptable.
3.
The licensee should provide the following within 60 days:
(a) Design details and a description of the operation of t'he proposed load shedding circuitry for the first level loss of voltage relaying.
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(b)
Details on how the load shedding feature will be bypassed when the onsite emergency generators are supplying power to the Class lE buses and how this feature will be reinstated if the onsite emergency generator breaker should trip.
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Technical Specifications to cover the setpoints and tolerances, limiting conditions for operation and surveillance testing for
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the undervoltage protective relaying system.
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(d)
Plant operating procedures to cover operator actions under degraded 1
grid and non-accident condi. tion.
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(e). A schedule for completion of all modifications to the first l
level (loss of voltage) and second level (degraded voltage) system.
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