ML20078L981
| ML20078L981 | |
| Person / Time | |
|---|---|
| Site: | South Texas  |
| Issue date: | 11/22/1994 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20078L965 | List: |
| References | |
| NUDOCS 9412010279 | |
| Download: ML20078L981 (3) | |
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NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 2055&o001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NOS. 66 AND 55'T0 FACILITY OPERATING LICENSE NOS. 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 DOCKET NOS. 50-498 AND 50-499 SOUTH TEXAS PROJECT. UNITS 1 AND 2
1.0 INTRODUCTION
By application dated April 29, 1994, as supplemented by letter dated September 8, 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 revise TS Table 3.7-1 and associated Bases by changing the maximum allowable power range neutron flux high setpoint when one or more main steam safety valves (MSSVs) are inoperable.
1 The September 8, 1994, supplement provided a summary of the calculation used as a basis for the proposed amendments.
The summary calculation does not change the initial proposed no significant hazards consideration determination.
2.0 BACKGROUND
Westinghouse has determined that the maximum allowable power range neutron flux high setpoints given in TS Table 3.7-1 may not be low enough to prevent a.
secondary side overpressurization during a loss of load / turbine trip.
In Nuclear Safety Advisory Letter (NSAL)94-001 dated January 20, 1994, Westinghouse provided the licensee with an algorithm to determine the revised neutron flux high setpoints.
The licensee requested that the Bases for TS 3/4.7.1.1 be changed to reflect the new algorithm and Table 3.7-1 be revised to reflect the new setpoint values. The setpoint values would be lowered from 87 percent, 65 percent, and 43 percent for 1, 2 or 3 inoperable MSSVs on any operable steam generator, respectively, to 63 percent, 45 percent, and 27 percent.
9412010279 941122 DR ADOCK 0500 8
_2 3.0 DISCVSSION The safety function of the MSSVs is to protect the steam generators and piping upstream of the main steam isolation valves from overpressure.
Bases Section 3/4.7.1.1 and TS 3.7.1.1 require the operability of the MSSVs to ensure that the secondary system pressure will not exceed 110 percent (1413.5 psig) of its design pressure (1285 psig) during the most severe anticipated system operational transient. The MSSVs are designed to relieve at least full power nominal steam flow.
TS 3.7.1.1 allows for plant operation with a reduced number of operable MSSVs at a reduced power level.
Should one or more MSSVs become inoperable, the power range neutron flux high setpoints will be reduced to the appropriate values to preclude a secondary side overpressurization condition. TS 3.7.1.1 was previously based on the assumption that the maximum allowable initial i
power level is = ?inear function of the available MSSVs relief capacity.
In NSAL-94-001, westinghouse determined that the maximum allowable initial power level is not a linear function of available MSSV relief capacity.
Therefore, operation with a reduced number of operable MSSVs at previously existing reduced power levels may not preclude a secondary side overpressurization, as explained below.
During loss of main feedwater, a reactor trip is necessary to prevent a secondary side overpressurization. At high initial power levels, a reactor trip is actuated early in the transient due to high pressurizer pressure or overtemperature delta T.
The reactor trip terminates the transient and MSSVs maintain steam pressure below 110 percent of the design value.
At low initial power levels, a reactor trip may not be actuated early in the transient. An overtemperature delta T trip is not generated since the core thermal margins are increased at lower power levels.
A high pressurizer pressure trip is not generated if the primary pressure control systems function normally. This results in a longer time during which primary heat is transferred to the secondary side. The reactor eventually trips on low steam generator water level, but this may not occur before steam pressure exceeds 110 percent of the design value if one or more MSSVs are inoperable in accordance with the previously existing TS.
4.0 EVALUATION The licensee calculated the new neutron flux high setpoints using the Westinghouse revised algorithm as follows.
For each case of one, two or three inopera' ole MSSVs on any operating steam generator, the minimum heat removal capability of the remaining operable MSSVs is calculated (this is done by summing the capacity of the operable MSSVs at the highest operable MSSV operating pressure, excluding the highest capacity MSSV(s)).
This heat removal capability would be then multiplied by number of loops in the plant to obtain the total heat removing capability from the secondary system using operable MSSVs.
The total heat removing capability from the secondary system is then compared to (i.e., divided by) the total heat input to the secondary system (from the primary system, using the nominal plant NSSS power rating) to obtain the new neutron flux high values.
With the new values, the heat input to the secondary system should not be greater than the heat removal capability
- of the secondary system, for each case of one, two or three inoperable MSSVs.
To provide additional assurance, the licensee then obtained the setpoints by lowering the values by 9 percent to compensate for instrument and channel uncertainties.
Based on the above, and the summary calculation provided by letter dated September 8, 1994, the staff finds that the revised algorithm ensures that the maximum power level allowed for operation with inoperable MSSVs is below the heat removing capability of the operable MSSVs. This ensures that the secondary system pressure will not exceed 110 percent of its design value.
In addition, the new setpoints are more conservative than the previous setpoints. Therefore, the staff finds that ibe proposed changes to TS Table 3.7-1 and Bases 3/4.7.1.1 are acceptable.
5.0 SJATE CONSULTATION 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.
6.0 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 29628). Accordingly, the amendments meet the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9).
Fursuant to 10 CFR 51.22(b) no environmental impact statement or environmental assessment need be prepared in connection with the issuance of the amendments.
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7.0 CONCLUSION
The Commission has concluded, based on the considerations discussed above, that:
(1) these is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, (2) such i
activities will be conaucted 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.
Princisal Contributors:
A. Bryant T. Alexion Date, L: limber 22, 1994