ML17341B470
| ML17341B470 | |
| Person / Time | |
|---|---|
| Site: | Turkey Point  |
| Issue date: | 10/28/1982 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML17341B469 | List: |
| References | |
| NUDOCS 8211110546 | |
| Download: ML17341B470 (6) | |
Text
ENCLOSURE 1
SAFETY.EVALUATI'ON TURKEY POINT NUCLEAR GENERATING PLANT, UNITS 3
& 4 DOCKET HOS. 50-250/251 DEGRADED GRID VOLTAGE PROTECTION FOR THE CLASS lE SYSTEM.
INTRODUCTION AHD
SUMMARY
The criteria and staff positions pertaining to degraded grid voltage protection were transmitted to Florida Power and Light Company by NRC Generic Letter dated June 3, 1977.
In response to this, by letters dated July 21, 1977, November 9, 1979, January 14, 1981 and May 10, 1982, the, licensee proposed certain design modifications and changes to the Technical Specifications.
A detailed review and technical evaluation of these proposed modifications,and changes to the Technical Specifications was performed by LLL, under contract to the HRC, and with general supervision
.by NRC staff.
This.work is reported by LLL in "De-graded Grid Protection for Class lE Power Systems Turkey Point Nuclear Generating Plant Units 3 and 4" (attached).
Me have reviewed this technical evaluation report and concur in conclusion that additional information is required to complete the evaluation of the degraded grid'rotection for the Class lE power system.
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; IEEE Standard 279-1971
("Criteria for Protection Systems for Nuclear Power, Generating Stations" ); IEEE Standard 308-1977 ("Voltage Ratings for Electrical Power Systems and Equi pment - 60 Hz"); and staff positions defined in HRC Generic Letter to FPL dated June 3, 1977.
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PROPOSED CHANGES MODIFICATIONS AND DISCUSSION The existing undervoltage protection at Turkey Point consists of:
Two instantaneous loss of voltage relays on each 4160 volt Class lE buses with a setpoint of 40 to 50Ã of nominal.
The two-out-of-two logic is such that actuation of one of the two relays on.train "A" in conjunction with one of the two relays on train "8" will disconnect the offsite power source, initiate load shedding of the Class lE buses, start the emergency diesel and initiate load sequencing.
The load shedding feature is bypassed when the Class lE buses are being supplied by the diesel generators.
The following electrical system design modifications have been proposed by the licensee:
1.
Modify the existing loss of voltage relays so that the. relays of buses A and 8 are independent.
With these modifications actuation of both relays on bus A or bus 8 will initiate offsite source disconnection, load shedding, diesel generator starting and load sequencing only for the bus on which the undervoltage condition occurs.
2.
Installation of two inverse time undervoltage relays on each 4160 volt Class lE bus.
These relays will be connected in a two-out-of-two logic per bus and will provide the same functions as the loss of voltage relays above.
These relays will also be bypassed when the diesel generator is supplying the Class lE buses.
3.
Installation of two instantaneous relays on each 480 volt Class lE load center.
These relays wil'1 be connected in a two-out-of-two logic and intei locked with a safety injection (SI) signal.
When actuated concurrent
with an SI, these relays will initiate power source disconnection, diesel generator starting, load shedding and subsequent load sequencing.
The modifications proposed by the licensee provide undervoltage relay pro-tection for the 4160 volt and 480 volt Class lE equipment.
However, the licensee has not provided technical specifications for these relays which include the setpoints with tolerances, surveillance requirements and limiting conditions for operation.
Without the setpoints, time delays and tolerances, no determination can be made on what range of protection will be provided.
Without surveillance requirements and limiting conditions of operation, no assurance is provided that minimum number of protective devices will be operable to provide the desired protection.
In addition the licensee has not provided details on how the load shed feature on the 480 volt load centers will be bypassed while the diesel generators are supplying the Class 1E buses and reinstated if the diesel generator breaker should trip.
Also interlocking the 480 volt load center protective relays with an SI signal precludes providing protection to the 480 volt Class lE equipment under non-accident conditions.
CONC L US I'ONS We have reviewed the licensee submittals and the LLL Technical Evaluation Report
.and find that the following information is required to complete our evaluation:
l.
A verification analysis which demonstrates that the selected voltage/time setpoints with tolerances of the undervoltage relays will provide the required protection to"all Class lE equipment over the range of grid voltage variation and will minimize the effects of short duration voltage transients.
'2.
Technical specifications changes for the design modifications including setpoints (voltage and time) with tolerances, surveillance requirements
.and limiting conditions for operation (including action statements).
3; Verification that the time delay selected for the undervoltage relays is consistent with the maximum time delay assumed in the FSAR accident analysis for providing cooling to the core.
4.
.Verification that, the design modifications meet all applicable requirements of IEEE STD 279-1971.
5.
Design details on how the load shedding feature of the 480 volt load
. center protective relays will be bypassed when the diesel generators are supplying the Class lE buses and reinstated on a diesel generator trip.
6.
The proposed undervoltage relays on the 480 volt Class '1E load centers are interlocked with an SI'ignal and therefore provide no protection for the Class 1E equipment under non-accident conditions.
We require that the design be modified to provide this protection under both accident and non-accident conditions.
The design should be revised to include the above and modification details shall be submitted to show that undervoltage
- protection is provided to all -480 volt Class 1E equipment under all plant operating and accident conditions or justify why this protection is not required under non-accident conditions.
7.
Technical specifications which include the test requirements that demonstrate the full functional operability and independence of the onsite power system.
These tests shall
- 1) simulate a loss of offsite power in conjunction with
~
~
I a safety injection signal and;2) simulate interruption and subsequent reconnection 'of the onsite power "system to their respective buses.
After resolution of the above items with the licensee, PSB,will 'issue a
Supplement to this evaluation report.