ML20114B340
| ML20114B340 | |
| Person / Time | |
|---|---|
| Site: | South Texas  |
| Issue date: | 08/19/1992 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20114B337 | List: |
| References | |
| NUDOCS 9208260152 | |
| Download: ML20114B340 (4) | |
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?4 UNITED STATES
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NUCLEAR REGULATORY COMMISSION e
WASHINoTON, D.C. 20665 l
SAFETY EyflUATION BY THE OFFICE OF NUCL[jA REACTOR REGULATION RELATED TO AMENDMEN1-NR. 41 TO
,m FACILITY OPERATING LICENSE NO. NPF "
HOUSTON LIGHTING-& POWER COMPANY 4ITY PUBLIC SERVICE BOARD OF SAN ANTONIO
{ENTRAL POWER AND LIGHT COMPANY CITY OF AUSTIL TEXAS p_0CKET NO, 50-498 SOUTH TEXAS PROJECT. UNIT 1
'1.O INTRODUCTION JBy: application-dated. June' 12, 1990, (ST-HL-AE-3485), as supplemented by letter dated July 17,-1991'(ST-HL-AE-3829), Houston Lighting & Power Company, et.
. al., (the-licensee) requested changes to the Technical Specifications (Appendix A to Facility Operating License No. NPF-76) for Soutn Texas Project,
-Unitil.= The proposed chan'ges would delete the-autoclosure interlock (ACl)-
portionfof_ the-Surveillance Requirements pertaining to TS 3/4.5.6, Residual Heat Removal: System (RHR).- By _ letter dated July 17, 1991 (ST-HL-AE-3828), the
. staff was: advised that the licensee proposes to implement the change on Unit I during_the fourth refueling outage which will begin i_n Septe W e 1992. The-
' proposed: change-wasiimplemented on Unit-2 during the. second= r;."ueling outage
'in September 1991. The July 17, 1991, submittal providad additional clartfying information and did not change the' initial ne significant hazards consideration determination.
2.0 BACKGROUND
During_ normal operating conditions, a double. barrier between the high pressure reactor coolant system-(RCS) and the low pressure residual heat removal system (RHRS)iis provided,by two motor _-operated valves. These valves are closed when
.the RCS.'is hot and pressurized-(normal operating conditions) and'open when the
= RHRS is in operation. (cooldown or refuel). _ Each of these valves-is provided
- with> manual-controls onde main control board and has two automatic interlocks. associated with its control circuitry, the-Autoclosure Interlock
-(ACI) and the Open Permissive Interlock (OPI).
The OPI prevents inadvertent opening of the' suction / isolation valves when RCS pressure 1s above the. design pressure of the RHRS considering ;he RHR pump discharge pressure. The ACI ensures that both isolation valves are fully closed when RCS-is pressurized above RHRS design pressure.
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- However, during cold shutdown and refueling operations, inadvertent isolation of RHRS caused by failure of the ACI circuitry at times has resulted in loss of residual heat removal capaollity.
In February 1988, the Westinghouse Owners' Group evaluated the removal of the ACI circuitry on Westinghouse designed plants and issued WCAP-ll736, " Residual Heat Removal System Autoclosure Ir.terlock Deletion Report for the Westinghouse Owners Group," Volumes 1 and 2, Revision 0.
The staff completed the review of WCAP-ll736 and by letter dated August 8,
-1989, provided = safety evaluation (SE) which concluded that the information in the WCAP report can t- " sed to supplement plant-specific requests to remove the ACI.
In the SE, the staff found that the removal of the ACI for Westinghouse plants produces a not safety ben'efit provided that the following five key improvements are in place.
1.
An alarm should be added to each RHRS suction valve that will actuate if the valve is open and the pressure is high, 2.
Valve position indication to the alarm should be provided and power to the switches should not bc affected by power lockout of valve.
3.
Procedural improvements described in the WCAP should be implemented.
4.
Powei should be removed from the RHRS suction valves prior to their being leak-checked, if feasible.
5.
RHRS suction valves operators should be sized such that the valves cannot be opened against full system pressure.
3.0 [yALUAT10N The licensee referenced the approved Westinghouse Owners' Group (WOG) report 4
WCAP-ll736.
In this report, the South Texas Project, Unit 1 olant (STP-1) is shown to be similar to plants in Group 2 for which the reference plant is Callaway.
The RHRS at STP-1 consists of three ccmpletely separate trains, two isolation valves per train arranged in series on the inlet between the high pressure RCS and low pressure RHRS.
In addition, the RHRS'is completely contained inside the containment building. An RHRS interfacing system LOCA would release coolant to containment rather than bypass containment.
As retnmmended in the WCAP, the licensee performed a probPbilistic scopino analysis for a loss of RHR during an outage and determined that the deletion of the ACI results in a decrease in the likelihood of loss of RHRS.
For cold overpressurization protection, the licensee stated that cold overpressure protection is provided by the pressurizer power operated relief valves and that the RHRS cischarge relief valves are not required to operate to mitigate the consequence of a ovv en.ssurization event at low RCS
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. temperature.
The staff found this to be acceptable and it conforms to the WCAP report.
The removal of the ACI at STP-1 will consist of hardware changes and procedural enhancements which the staff believes will produce a net safety benefit compared to the current plant arrangement.
The hardware changes at STP-1 will consist of the addition of an alarm to each suction valve.
The alarm will actuate if the valve is open and the pressure is greater than the
- open permissive setpoint and less than the RHR design pressure minus the RHR pump head pressure. The OPI will not be affected by the addition of the alarm and the removal of the ACI circuitry.
The valve position indication will be provided from the spare Limitorque limit switch contacts on the RHR suction valve. The power to these~ contacts is provided by separate power supply such that the alarm and valve position indication in the control room will still be available following power lockout of the RHR suction valves.
The licensee has identified procedural modifications that will be completed and implemented by the time the ACI deletion is completed.
The alarm response procedure used during plant startup will be modified to reflect the alarm recognition responses for the added alarm.
The procedure will be revised to direct-the operator to take the necessary actions to close the open RHR suction valves once the alarm is initiated.
If this is not possible the operator will be instructed to depressurize the RCS to return to non-alarm condition.
In addition, test procedures for the aiarm will be added to verify that the alarm remains operable.
One of the staff's recommendations was that the valve be leak-tasted after the power to the valve has beea removed, if feasible, to ensure that the valve is closed. The licensee stated that the suction valves will be leak-tested prior to returning tLe valves to service.
However, this leak test is to be performed at low temperature and without first removing power due to personnel safety _ considerations. The staff finds this to be acceptable as the licensee provides position verification to ensure that the valve-is actually closed when power is removed following the leak test.
This is required by Step 8.8 of.the procedure POP 3ZG0001 for plant heatup that references procedure POP 2RH0001 Step 8.0 in which there is a requirement for verification of RHR suction valve closure by indication on the Main Control Board.
The ' licensee reviewed the sizing of the RHR suction vah:es ana stated that they are sized such th:.t it would be unlikely that these valves could be opened against full system pressure.
The staff has reviewed the South Texas Project, Unit I submittal and has und that the licensee meets the -requirements-for the removal of the autoclosur e interlock by implementing the hardware and procedural modifications. The proposed amendment to delete ACI from the Technicai Specifications for Unit I and from the UFSAR is therefore acceptable.
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4.0 STATE CONSULTATION
In accordance with the Commission's regulations, the Texas State official was notified of the proposed issuance of the amendment. The State official had no comments.
5.0 ENVIRONMENTAL CON 51 DERAT 10N The amendment changes a requirement with respect to installation or use of a facility component located within the restricted area as defined in 10 CFR Part 20 and changes surveillance requirements.
The NRC staff has determined that the amendment involves no significant increase in the umounts, 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 previously issued a proposed finding that the amendment involves no significant hazards consideration, and there has been no public comment on such finding (55 FR 34371). Accordingly, the amendment meets the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9).
Pursuant to 10 CFR SI.22(b) no environmental impact statement or environmental assessment need be prepared in connection with the issuance of the amendment.
6.0 CONCLUSION
The Commission has 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, (2) such activii.ies will be conducted in compliance with the Commission's regulations, and (3) the-issuance of the amendment will not be inimical to the common defense and security or to the health and safety of the public.
Principal Contributor:
L. Tran Date:
August 19, 1992