ML20071Q716
| ML20071Q716 | |
| Person / Time | |
|---|---|
| Site: | South Texas  |
| Issue date: | 08/03/1994 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20071Q706 | List: |
| References | |
| NUDOCS 9408110330 | |
| Download: ML20071Q716 (3) | |
Text
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UNITED STATES (igy NUCLEAR REGULATORY COMMISSION g
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WASHINGTON, D.C. 2055'HX)01 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NOS. 63 AND 52 TO FACILITY OPERATING LICENSE N05. NPF-76 AND NPF-80 HOUSTON LIGHTING & POWER COMPANY i' ~
CITY PUBLIC SERVICE BOARD OF SAN ANTONIO CENTRAL POWER AND LIGHT COMPANY CITY OF AUSTIN. TEXAS D0_CKET NOS. 50-498 AND 50-499 SOUTH TEXAS PROJECT. UNITS 1 AND 2
1.0 INTRODUCTION
By application dated March 16, 1994, Houston Lighting & Power Company, et.al.,
(the licensee) requested changes to the Technical Specifications (TSs)
(Appendix A to Facility Operating License Nos. NPF-76 and NPF-80) for the South Texas Project, Units 1 and 2 (STP).
The proposed changes would modify Figure 3.4-4, " Nominal Maximum Allowable PORV Setpoint for the Cold Overpressure System," for the cold overpressure mitigation system with a revised setpoint curve.
2.0 BACKGROUND
The reactor coolant system (RCS) pressure-temperature (P/T) limits during plant heatup and cooldown for South Texas Project Electric Generating Station, Units 1 and 2 are specified in TS Figures 3.4-2 and 3.4-3, and are applicable up to 32 effective full power years (EFPY).
The pressurizer power operated relief valves (PORVs) setpoints for overpressure mitigation are specified in TS Figure 3.4-4.
By letter dated March 16, 1994, Houston Lighting and Power Company submitted an application to modify TS Figure 3.4-4 (for PORV setpoints).
The proposed changes incorporated corrections for a nonconservative item in the original setpoint study.
The methodology used in developing the modified TS Figure 3.4-4 is provided in WCAP-13782, Revision 2, "Setpoint Program Determination for the Westinghouse Cold Overpressure Mitigating System in the Houston Lighting & Power, South Texas Units 1 and 2," dated February 1994.
The new PORV setpoints provide protection against a potential overpressurization during low temperature plant conditions with either two or four reactor coolant pumps (RCPs) in operation.
9408110330 940803 PDR ADOCK 05000498 p
- 3.0 EVALVATION In the current TSs, when the reactor is operated at Modes 4, 5 and 6 and when the head is on the reactor vessel, low temperature overpressure protection (LTOP) is provided by either of the pressurizer PORVs with lift settings specified in TS Figure 3.4-4.
These settings were developed to avoid RCS pressures from exceeding either the reactor vessel Appendix G limit, or 800 psig at the PORVs, whichever is the most limiting.
The 800 psig was included to limit the loads on the PORV discharge piping and supports when the PORVs cycle (open and close) during a subcooled water discharge, which could occur during design basis cold overpressure events.
Either PORV has adequate relieving capacity to protect the RCS from overpressurization when the transient is limited to either (1) the start of an idle RCP with the secondary water temperature of the steam generator less than or equal to 50 F above the RCS cold leg temperature; or, (2) the mass injection flow rate due to the startup of a single high head safety injection (HHSI) pump plus 100 gpm net charging flow, while the RCS is in a water solid condition, and RCS temperature is between 350 F and 200 F.
For RCS temperature less than 200 F, the mass addition event consists of operating a centrifugal charging pump with complete termination of letdown flow.
By letter dated March 16, 1994, the licensee proposed a change in the PORV settings. This change was proposed by the licensee as a corrective action in response to a nonconservative item that was discovered in late 1992. This nonconservative item is that the pressure difference between the wide range pressure sensor and the reactor vessel location where the Appendix G limit is applicable, was not taken into account in the calculation of limits.
This pressure difference effectively results in the pressure in the reactor vessel being greater than that seen by the wide range pressure transmitters, and therefore potentially resulting in violation of the Appendix G limit during a transient.
Shortly following the discovery of this, the lic,ensee implemented a temporary correction by lowering the PORV setpoints by 35 psi with only two RCPs in operation during low temperature operating conditions. The licensee has recently performed reanalysis to determine the correct PORV setpoints for either two or four RCPs in operation. The methodology used for developing the new setpoints is documented in WCAP-13782, Rev. 2.
Heatup and cooldown curves for isothermal conditions and without instrument errors, applicable to 32 EFPY, were utilized for the Appendix G limit.
The calculation associated with the Appendix G limit is documented in Appendix A of WCAP-13782, Rev. 2.
The licensee considers that the use of isothermal curve for developing PORV setpoints is appropriate since the majority of the past overpressure transients were occurring during isothermal conditions.
The staff agrees with this assessment in developing the new PORV setpoints.
Both mass input and heat input overpressure transients are considered, which are consistent with the assumptions made in the previous setpoint study.
The licensee's proposed changes in TS Figure 3.4-4 reflect the changes discussed above.
The staff has reviewed the licensee's submittal and finds that the changes are based on applicable regulatory guidance in Standard Review Plan 5.2.2 (Revision 2), are reasonably conservative, and are acceptable.
i
o i 4.0 STATE CONSVLTATION t
In accordance with the Commission's regulations, the Texas State official was notified of the proposed issuance of the amendments.
The State official had no comments.
5.0 ENVIRONMENTAL CONSIDERATION
The amendments change 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 amendments involve 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 increase in individual or cumulative occupational radiation exposure. The Commission has previously issued a proposed finding that the amendments involve no significant hazards consideration, and there has been no public comment on such finding (59 FR 17601).
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 amendments.
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 amendments will not be inimical to the common defense and security or to the health and safety of the public.
Principal Contributor:
C. Liang, NRR Date: August 3, 1994 4
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