ML20116P344
| ML20116P344 | |
| Person / Time | |
|---|---|
| Site: | Summer  |
| Issue date: | 04/30/1985 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20116P341 | List: |
| References | |
| NUDOCS 8505080008 | |
| Download: ML20116P344 (4) | |
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UNITED STATES
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NUCLEAR REGULATORY COMMISSION L
ij WASHINGTON, D. C. 20655
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO. 40 TO FACILITY OPERATING LICENSE NPF-12 SOUTH CAROLINA ELECTRIC & GAS COMPANY
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SOUTH CAROLINA PUBLIC SERVICE AUTHORITY I.
INTRODUCTION By letter dated August 24, 1984, South Carolina Electric and Gas Co:npany (the licensee) requested Technical Specification changes in the trip set-point requirements for the low-low steam generator reactor trip and the overtemperature delta-T trip. Data taken during the startup test program revealed that the plant did not have the capability to handle a full load rejection without tripping using the original setpoints. The requested modifications, together with a modification to the steam dump control setpoint, would allow the plant to accomodate a complete loss of external load in accordance with the original design as described in the FSAR.
Modification to the steam dump control setpoint does.not involve a Tech-nical Specification change.
In response to NRC staff questions, the licgige. subm}ted additional information.by. letter jfa_ted November 14, 1984.
This amendment request of August 24, 1984, was_ noticed in the Federal Register (50 FR 12162) on March 27, 1985, as including a change to T in 4
the overtemperature delta-T trip setpoint equation. By amendment No. 28 to NPF-12.(October 12,1984), time constant T was renumbered to be T,
l and T, was eliminated. Therefore, ti:ne const$nt T is actually being 1 i
chang 6dhbut it is the same time constant as that requested originally and noticed. Therefore, this amendment request is not being renoticed.
II. EVALUATION i
i Steam generator level (narrow range) for the Westinghouse Model D steam i
generator is measured within the downcomer region. Sudden reductions in j
steamflow caus*e a rapid drop in downcomer level. The level change is I
caused by the redistribution of water within the steam generator and not l
by change in the total water mass.
The licensee requested that the reactor trip setpoint be changed for the steam generator water level low-low signal. Currently, this setpoint is linear from 12% to 54.9% of span for 30% to 100% of rated thermal power (RTP). This would be changed to 12% to 30% of span for 30% to 100% of RTP. Also, the allowable value associated with the trip setpoint is.being changed a corresponding amount. The low-low level trip setpoint is relfed upon in the FSAR to trip the reactor and initiate auxiliary feedwater following loss of main feedwater. A 0% level on the narrow range was assumed for the setpoint in the FSAR. The revised setpoint is 5.8 feet above the FSAR assumption. The revised setpoint is within the bounds of the current safety analysis and is, therefore, acceptable.
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2-The change proposed by the licensee to the overtemperature delta-T set-point equation involves changing the time constant T from 33 seconds to 3
28 seconds. The decrease in the time constant T will decrease the com-3 pensation to the reactor core average temperature and, consequently, reduce the penalty to the,overtemperature delta-T setpoint cW by increases in the core average temperature.
The licensee states that, of the seven safety analyses listed under over-temperature delta-T in FSAR Table 7.2-4, only four take credit for a reactor trip initiated by the overtemperature delta-T protection circuit. These events are:
1.
Uncontrolled rod withdrawal at power 2.
Uncontrolled boron dilution at power 3.
Loss of load transient 4.
Accidental depressurization of the reactor coolant system The other three safety analyses (excessive heat removal, excessive load increase, and accidental depressurization of the main steam system) do not take credit for a reactor trip based on,the overtemperature delta-T protection circuit.-- The-overtemperature delta-T trip does; however, provide a backup trip.. For these three transients and the accidenta1 depressurization of the reactor coolant system, the core average temperature decreases result-ing in a credit to the overtemperature delta-T setpoint. The decrease in the time constant T delays this credit and is conservative for these 'four 3
events. The proposed decrease in T is, therefore, acceptable for these i
four eve (its. The remaining three e9ents are evaluated below.
Uncontrolled Rod Withdrawal at Power This event is protected by the overtemperature delta-T trip for low re-activity insertion rates and by the high flux trip for high reactivity insertion rates. The limiting departure from nucleate boiling ratio (DNBR) can be plotted for a given core power and moderator feedback as a function f{
of reactivity insertion rate. The two trips overlap to some degree. The 1
effect of decreasing the time constant T will cause the high flux trip i
l to become effective for this event at a somewhat lower reactivity insertion
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rate. The DNBR, however, never becomes less than the Technical Specification limiting value. We find, therefore, that the decrease in T is acceptable l.
for this event.
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Uncontrolled Boron Dilution at Power l
This event requires operator action both to recognize that the reactor is undergoing the event and to terminate the event with acceptable consequences, j
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, 4 The safety analysis indicates that the operator has 43.2 minutes after a trip to stop the dilution. A change in the time constant T which is 3
proposed here changes this. time to 43 minutes. The decrease in the time available to the operator to terminate the boron dilution is insignificant.
We find, therefore, that the decrease in T is acceptable for this event.
1 Loss of Load Transient This event is protected by the overtemperature delta-T trip when the pres-e curizer pressure control is assumed to function and by the high pressurizer pressure trip when the pressurizer pressure control is not assumed to be operable.
For a beginning of the life event with pressurizer pressure
. control,-the decrease in T, results in a slight delay in the overtempera-i ture delta-T trip and a sitghtly lower minimum DNBR of 1.50 which is well
. above the Technical Specification limiting DNBR value of 1.30.
For the end of life case with pressurizer pressure control, the decrease in T again results in a slight delay in the overtemperature delta-T trip. 7The i
DNBR does not decrease below its initial.value because of the decrease in
. reactor power caused by the large negative moderator coefficient and the increase in pressurizer pressure. We find, therefore, that the decrease in T is acceptable for'this event.
y Based on our review, we conclude that the proposed changes are acceptable because the effect on FSAR safety ~analy'ses has been demonstrated to.n.ot
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V excETapplicable criteria.
III. ENVIRONMENTAL CONSIDERATION This amendment involves a change in the use of a facility component located within the restricted area as defined in 10 CFR Part. 20. The staff has l'
detemined that the amendment involves no significant increase in the
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amounts,'and no significant change in the types, of any effluents that may be released offsite and that there is no significant increase in individual-or cumulative occupational radiation exposure. The Commission has previous-ly issued a proposedsfinding that this amendment involves no significant hazards consideration, and there has been no public coment on such finding, Accordingly, this amendment meets the eligibility criteria for categorical t.-
exclusion set forth in 10 CFR Sec 51.22(c)(9). Purusant to 10 CFR 51.22(b) no environmental impact statement or environmental assessment need be pre-pared in connection with the issuance of this amendment.
IV. CONCLUSION The Commission made a proposed determination that the amendment involves no significant hazards consideration which was published in the Federal Register (50 FR 12162) on March 27, 1985, and consulted with the state of South Carolina. No public comments were received, and the state of South Carolina did not have any comments.
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We have concluded, based on the considerations discussed above, that:-
(1) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, and (2) such activities will be conducted in compliance with the Commission's regulations, and the issuance of this amendment will not be inimical to the common defense and security or to the health and safety of the public.
Principal Contributors: Jon B. Hopkins, Licensing Branch No. 4, DL Walton L. Jensen, Reactor Systems Branch, DSI Daniel B. Fieno, Core Performance Branch, DSI Dated: April 30, 1985
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