ML20083E458
| ML20083E458 | |
| Person / Time | |
|---|---|
| Site: | South Texas  |
| Issue date: | 09/18/1991 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20083E444 | List: |
| References | |
| NUDOCS 9110020376 | |
| Download: ML20083E458 (5) | |
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UNITED STATES nf NUCLEAR REGULATORY COMMISSION
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WASH ActoN. o c. rows g s. c j SAFETY EVALUA110N BY 1HE OFFICE OF NUCLEAR REAC10R REGULATION RELATED 10 AMENDMENT NO.18 TO FAClll1Y OPERATING LICENSE NO. NPF-80 HOUSTON LIGHTING & POWER CO'iPANY CITY PUBLIC SERVICf BOARD OF SAN ANTONIO CENTRAL POWER AND LIGHT COMPANY CITY OF AUSTIN, TEXAS DOCKET NO. 50-499
_SOU1H 1EXA5 PROJECT, UN11 2
1.0 INTRODUCTION
By application dated June 12, 1990 (51-HL-AE-3485), Houston Lighting & Power Company, et. al., (the licensee) requested changes to the Technical Specifications (Appendix A to facility Operating License Nos. NPF-76 and NPF-80) for South Texas Project Units 1 and 2.
ihe proposed changes would delete the autoclosure interlock (ACl) portion of the Surveillance Requirements pertaining to 15 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 2 during the second refueling outage which will begin in September 1991.
The proposed change will be implemented on Unit I during the fourth refueling outage which is scheduled to begin in October 1992.
The July 17, 1991, submittal provided additional clarifying information and did not change the initial no significant hazards consideration determination.
2.0 BACKGROUND
During normal operating conditions, a double barrier between the high pressure reactor coolant system (RCS) ant' he low pressure residual heat removal system (RHRS) is 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 manaal controls on the main control board and has two automatic interlocks associated with its control circuitry, the Autoc'iosure Interlock (ACl) and the Open Permissive Interlock (OPI).
The OPI prevents inadvertent opening of the suction / isolation valves when RCS pressure is above the design pressure of the RHRS considering the RHR pump discharge pressure.
The ACI ensures that both isolation valves are fully closed when RCS is pressurized above RHR5 design pressure.
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, SAFETY EVALVATION BY 1Hf OfflCE,0f NUCLEAR REAC10R REGULA110N RELA 1ED TO AMrNDMENT_ NO._18 10 FAClllli OPERAllNG LICENSE NO. NPF-80
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CITY PUBLIC SERVICE BOAR 0 0F SAN AN10NI,0 CENTRAL POWER AND LIGHT COMPANY CITY Of AUSTIN, TEXAS DOCKE1 No. 50-499 SOUTH TEXA5 PROJECT, UNil 2
1.0 INTRODUCTION
Dy application dated June 12,1990 (ST-HL-AE-3485) Houston Lighting & Power Company, et. al., (the licensee) requested changes to the Technical Specifications (Appendix A to facility Operating License Nos. NPT-76 and NPF-80) for South Texas Project, Units 1 and 2.
The proposed changes would delete the autoclosure interlock (ACl) portion of the Surveillance Requirements pertaining to 15 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 2 during the second refueling outage which will begin in September 1991.
The proposed change will be implemented on Unit I during the fourth refueling outag3 which is seneduled to begin in October 1992.
The July 17, 1991, submittal provided additional clarifying information and did not change the initial no 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) is 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 (couldown or refuel).
Each of these valves is provided with manual controls on the main control board and has two automatic interlocks associated with its control circuitry, the Autoclosure Interlock (ACl) and the Open Permissive Interlock (OPI).
The OPI prevents inadvertent opening of the suction / isolation valves when RCS pressure is above the design pressure of the RHRS considering the RHR pump discharge pressure.
The ACI ensures that both isolation valves are fully closed when RCS is pressurized above RHR5 design pressure.
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However, during cold shutdown and refueling operations, inadvertent isolation of the RHRS caused by failure of the ACI circuitry at times has resulted in loss of residual heat removal capability.
In february 1988, the Westinghcuse Owners' Group evaluated the removal of the ACI circuitry on Westinghouse designed plants and issued WCAP-11736, " Residual Heat Removal System Autoclosure Interlock Deletion Report for the Westinghouse Owners Group," Volume. and 2, Revision 0.
The staff completed the review of WCAP-11736 and by letter dated August 8,1989, provided a safety evaluation (SE) which concluded that the information in the WCAP report can be used 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 net safety benefit 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 be affected by power lockout of valve.
3.
Procedural improvements described in the WCAP should be implemented.
4.
Power 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 EVALUATION The licensee referenced the approved Westinghouse Owners' Group (WOG) report WCAP-11736.
In this report, the South Texas Project, Units I and 2 plants (STP-1 and STP-2) are shown to be similar to plants in Group 2 for which the reference plant is Callaway.
The RHRS at STP-1 and STP-2 consists of three completely 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 cociant to containment rather than bypass containment.
As recommended in the WCAP, the licensee performed a probabilistic scoping 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.
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for cold overpressurization protection, the liernsee stated that cold over-pressure protection is provided by the pressurizer pcwer operatec rellet valves and that the RHRS discharge relief valves are not required to operate to mitigate the consequence of a overpretsurization event at low RCS temperature.
The staff found this to be acceptabla and it conforms to the WCAP report.
The removal of the ACI at SIP-1 and STP-2 will consist of hardware changes and procedural enhancements which the staff believes will produce a net safety l
benefit compared to the current plant arrangement.
The hardware changes at STP-1 and STP-2 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 OPl 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 tha spare timitorque 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 r
direct the operator to take the necessary actions to close the open RHR suction valves once the alarm is initiated.
If this is i...t possible the operator will be instructed to depressurize the RCS to return to non-alarm condition.
In addition, test procedures for the alarm will be added to verify that the alarm remains operable.
One of the staff's recommendations was that the valve be leak-tested after the power to the valve has been removed, if feasible, to 2nsure that the ialve is closed.
The licensee stated that the suction valves for STP-1 and STP-2 will be leak-tested prior to returning the 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 valves and stated that
-they are sized such that it would be unlikely that these valves could be opened against full' system pressure.
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The staff has reviewed the South Texas Project, Units I and 2 submittal and has found that the licensee meets the requirements for the removal of the autoclosure l
interlock by implementing the hardware and procedural modifications.
The l
proposed amendment to delete ACI from the Technical Specifications for Unit 2 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 ENV!w0NMENTAL CONSIDERATION 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 amounts, and no significant change in the types, of any effluents that may be released of fsite, 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 51.22(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 activities 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:
September 18, 1991 1
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