ML20086D946
| ML20086D946 | |
| Person / Time | |
|---|---|
| Site: | South Texas  |
| Issue date: | 11/08/1991 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20086D944 | List: |
| References | |
| NUDOCS 9111260335 | |
| Download: ML20086D946 (6) | |
Text
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MsHWoToN. D. C. 7055s a
SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION e...*
RELATED TO AMENDMENT NOS. 31 AND 22 TO 1
FACILITY OPERATit/G LICENSE N05. NPF-76 AND NPF-80 HOUSTON LIGHTING & POWER COMPANY CITY PUBLIC SERVICE BOARD OF SAN ANTONIO CEfMRAL POWER AND LIGHT COMPANY CITY OF AUSTIN. TEXAS j
DOCKET NOS. 50-498 AND 50-499 SOUTH TEXAS PROJECT, UNITS 1 AND 2
- 1. 0 INTRODUCTION By application dated December 21, 1990 (ST-HL-AE-3642), and as supplemented by letter dated October 11., 1991, Houston Lighting & Power Company, et, al, (the licensee) requested changes to the Technical Specifications (TS) (Appendix A to Facility Operating License Nos. NPF-76 and NPF-80) for the South Texas Project, Units 1 and 2.
The majority of the proposed changes were in response to Generic Letter 90-06, " Resolution of Generic Issue 70, ' Power-Operated Relief Valve and Block Valve Reliability,' and Generic Issue 94, ' Additional Low-Temperature Overpressure Protection for Light-Water Reactors." The licensee also addressed a conflict in the TS between TS 3.4.9.3 and TS 4.0.5 which would not permit full operability testing of inoperable pressurizer power-operated relief valves (PORVs) following maintenance on the FORVs.
This safety evaluation addresses the pressurizer PORV testing issue.
Clarifying information in support of the amendment request was provided by the licensee's letter dated October 15, 1991 (ST-HL-AE-3893).
The October 15, 1991, submittal did not change the initial no significant hazards consideration determination.
- 2. 0 BACKGROUND Technical Specification 3/4.4.9, Pressure / Temperature Limith Reactor Coolant System, establishes the limiting reector coolant system (RCS) pressure and temperature for all operating modes.
The requirements for the overpressure protection systems are given in Limiting Condition for Operation (LCO) 3.4.9.3.
This LCO states that two power operated relief valves (PORVs) are to be operable during Modes 4 and 5, and Mode 6 with the head on the reactor vessel, or that the RCS be depressurized with an RCS vent af greater than or equal to 2.0 square
- inches, Ar. tion a. of this LCO states that with one PORV inoperable, the inoperable PORV is to be restored to OPERABLE status within 7 days or the 9111260335 911100 PDR ADOCK 05000490 P
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reactor pressure vessel (RPV) is to be depressurized and vented through a 2.0 square inch vent within the next 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br />.
Action b, of this LCD states that with both PORVs inoperable, depressurization and venting of the RCS through a 2.0 square inch vent is required within 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br />.
Pressurizing the RCS to stroke test a Pressurizer PORV following the performance of required maintenance or *epcirs as required by Technical Specification 4.0.5 creates a conflict with Technical Specification 3.4.9.3 requirements since a nominal test pressure is required to overcome the internal spring pressure of the solenoid operated PORVs.
The required test provides verification of valve operability in accordance with the ASME code requirements.
This proposed test complies with the requirements of Technical Specification 4.0.5 and the intent of Generic Letter 90-06.
Prior to this test the ANALOG CHANNEL OPERATIONAL TEST specified in Surveillance Requirement 4.4.9,3.1.a would be performed to provide reasonable assurance that the administratively declared inoperable PORV will function if required.
The ASME operability test cannot be performed without suspending the requirement to depressurize and vent the RPV if one er both PORVs are inoperable since a nominal reactor coolGnt system pressure is necessary to perform the test and the test cannot be conducted within the time allowed by the LCO.
{V,ALUATION 3.0 V
The proposed TS change to allow the utilization of the residual heat removal (RHR) relief valves for low temperature overpressure (L10P) protection on a temporary basis during testing of the PORVs requires evaluation regarding the ability of the RHR relief valves to fulfill the LTOP function and the potential impact of relief valve actuation on the operation of the RHR system.
In addition, evaluation of the specifics associated with the proposed TS change such as the seven day allowed outage time for the PORVs and tit administrative limits associated with LTOP protection are also important in the evaluation.
The proposed TS change would allow the RHR relief valves to serve as an alternate to the normal L10P protection provided by the PORVs for a period of up to seven days.
This allowance is required to compensate for an existing TS conflict which requires PORV operability or RCS depressurization during Mode 5 (cold shutdown) even though entry into Mode S is required to perform the ASME Section XI testing due to the need to reach an RCS pressure which overccmes th( PORV spring force.
The proposed TS change would allow an RHR relief valve to serve as LTOP protection in place of an inoperable PORV prior to the completion of the PORV'sSection XI testing.
If both PORVs were declared inoperable, two RHR relief valves are proposed to be acceptable.
Conditiv.15 placed upon the use of the RHR relief valves for the LTOP function include; the associated RHR loop (s) must be operable and operating, the RHR suction valve auto closure interlocks must be bypassed or removed, and the time period in which this condition is acceptable is limited to seven days.
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3.1 Hlnimize Occurrence of an Overpressurization Event In addition to TS 3.4.9.3 with its associated proposed revision, the following administrative controls and TS requirements minimize both the potential for and the consequences of an overpressurization event during plant heatuo and PORV testing:
When RCS pressure is being maintained by the icw pressure letdown control a.
valve, the normal letdown orifices are bypassed but not isolated, b.
Only one centrifugal charging pump (CCP) will be allowed to be operable; this minimizes the potential for a mass input overpressure transient, Administrative controls will be in place to ensure that the high head c.
safety injection (HHSI) pumps will not operate during water solid operations with the PORV(s) inoperable to minimize the potential for creating a cold overpressure transient.
d.
The RCS pressure will be controlled at the minimum value necessary to perform the required testing of the inoperable PORV(s) (325-400 psig).
A reactor coolant pump shall not be started with one or more of the RCS e.
cold leg temperatures less than or equal to 350 F unless the secondary side water temperature of each steam generator is less than 50*F above the RCS cold leg temperature (TS 3.4.1.4.1.a).
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The positive displacement pump will be demonstrated inoperable during the water solid operations to minimize the potential for a mass input over-pressure event.
g.
The RHR auto closure interlock will be bypassed (Unit 1) or deleted (Unit 2) during water solid operations _to prevent the loss of letdown capability which could produce a mass input overpressure event.
- 3. 2 Mitigation of an Overpressurization Event If an overpressurization event occurs, its mitigation is based upon the relief capacity of the PORV(s) and the RHR relief valves as proposed by the TS change.
Although the PORV(s) are declared inoperable prior to the completion of the ASME Section XI testing, the valves will have undergone the required main-tenance during the outage and the cold overpressure mitigation system (COMS)/
LTOP-logic will be armed during the period in which the RHR relief valves will be recognized as the alternate LTOP protection system.
However, since the PORV(s) will not be declared operable until the ASME stroke testing has been satisfactorily completed, the licensee has evaluated the ability of the RHR relief valves to mitigate a potential cold overpressure event.
The RHR relief valve is located on the discharge of the RHR pump and will lift at the design setpoint of 600 psig plus 10 percent accumulation pressure.
With the RHR system operating, the RHR relief valve has been shown to open when the
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. i RCS pressure is approximately 589 psig.
The COMS/LTOP betpoint associated with the PORVs varies as a function of temperature and would be approximately 550 psig during the conditions associated with the performance of the ASME Section XI testing (a 60 psi allowance for measurement uncertainties results in an analytical setpoint of 610 psig).
The evaluation included conditions associated with reactor coolant pumps operating, as well as idling, and in both cases the RHR relief valves were determined to lif t at RCS pressures comparable to the PORY related COMS/LTOP channels.
The protection provided by the RHR relief valves is dependent upon their relief capacity in addition to the relief pressure setpoint.
The mass addition transient considered during COMS/LTOP assumes a loss of letdown and a fai. led open charging valve.
This results in a mass addition transient of 410 ppm.
The transient is based upon the lockout of all HHS! pumps, low head safety i
injection (tHSI) pumps (LHSI pumps developed head is 315 psig and are therefore i
not significant to COMS/LT0P event even if operable), one CCP, and a positive displacetrent pump (PDP) during Modes 5 and 6.
The RHR relief valves are designed to relieve 810 gpm flow with all charging pumps operating at full i
capacity, based on complete loss of letdown, and the charging flow control valve in the failed wide open position.
The relief capacity and lift pressure associated with the RHR relief valve (s), combined with other administrative and TS limits, are considered adequate to mitigate the design cold overpressure event.
A consideration is whether actuation of the RHR relief valve (s) might affect RHR operability and thereby prevent the fulfillment of the LTOP function.
In this regard, the licensee evalrated the potential for RHR pump runout and subsequent pump damage if the RHR relief valves opened to provide LTOP protection.
Based upon calculations and RHR pump runout tests performed on STP Unit 2 prior to operation, the licensee determined that pump runout conditions would not result if the relief valves lifted during system operation.
The calculatiens considered the RHR system pressure losses associated with pump runout and system operation during the period the RHR relief valves would be serving as the LTOP protection concurrent with the failure of the RHR heat exchanger outlet valve.
The calculations determined that RHR pumps would not achieve the pump runout design flow of 4000 gpm during a mass addition accident.
Unit 2 hot functional testing included testing of the RHR pumps due to pump runout concerns associated with increasing the RHR pumps miniflow line capacity.
Operation of the pumps at or near the design runout conditions of 4000 gpm showed no indications of pump cavitation, vibration, or motor current exceeding manufacturer recommenda-tions.
Pump tiows associated with those plant conditions in which the RHR relief valves would be providing LTOP protection are significantly less than the flows associated with the pump runout tests performed during Unit 2 hot functional testing.
The miniflow line is isolated after the successful starting of an RHR pump and thus this flow path does not contribute to the pump runout concerns associated with the RHR relief valves LTOP function.
The calculations and tests support the conclusion that the RHR system would remain operating during an overpressurization event in which the RHR relief valves lifted to provide LTOP protection.
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. 3.3 Seven Day Suspension of the Action Statement The seven day suspension period has been determined based upon the schedule of events associated with performance cf the PORV testing and an evaluation of the protection provided by proposed LTOP function of the RHR relief valves and the administrative controls to limit the consequences of an overpressurization event.
The events include the preparation for and subsequent filling and venting of the RCS, establishment of a letdown flow path, addition of heat to the RCS, forming a bubble in the pressurizer, performing surveillance on the reactor vessel head vent system, and performance of the PORV stroke testing.
Considering the time associated with these activities and the provision of adequate margin for contingencies, the staff believes that an allowed PORV outage time of seven days is acceptable.
The justification for the seven day allowed PORV outage time included a review of the adfinistrative controls in place to prevent and/or limit the consequences of an overpressurization event as well as the capability of the RHR relief valves to perform the LTOP function.
As discussed above, the RHR relief valves combined with the other administrative and TS requirements have been demonstrated to provide adequate LTOP protection during Mode 4 operation prior to the completion of the PORV ASME Section XI testing.
4.0
SUMMARY
The licensee has demonstrated that the RHR relief valves can adequately serve as a substitute for the PORVs for LTOP protection during Mode 5 operation prior to the completion of the PORV ASME Section XI testing.
The RHR relief valves have sufficient flow capacity and relief setpoints to mitigate a cold over-pressure event.
In addition, it has been shown through calculations and testing that the RHR system remain operable during a cold overpressure event with the RHR relief valves open to provide LTOP protection.
Based upon its review of the proposed TS revision and the justifications discussed above, the staff has concluded that the proposed change to TS 3.4.9.3 which adds the RHR relief valve (s) as an acceptable alternate to the PORV(s) for LTOP protection f:r : ;:criod not to exceed seven days is acceptabla.
5.0 STATE CONSULTATION
In accordance with the Commission's regulations, the Texas Stata official was notified of the proposed issuance of the amendment.
The State official had no comments.
6.0 ENVIRONMENTAL LONSIDERATION 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.
The NRC staff has determined that the amendment involses no significant increase in the amounts, and no significant change in the types, of any effluents that may be released offsite, and that there is no significant i
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4 6-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 (56 FR 49918).
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 envitonmental impact statement or environmental assessment need be prepared in connection with the issuance of the amendment.
7.0 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 Contributors:
William Reckley Chu-Yu Liang Date:
November 8, 1991
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