ML20086Q980
| ML20086Q980 | |
| Person / Time | |
|---|---|
| Site: | South Texas  |
| Issue date: | 07/25/1995 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML20086Q974 | List: |
| References | |
| NUDOCS 9507280280 | |
| Download: ML20086Q980 (4) | |
Text
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UNITED STATES
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j NUCLEAR REGULATORY COMMISSION j i!
c wAssiwatow, o.c. rosswoos s...+f SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT N05. 78 AND 67 TO FACILITY OPERATING LICENSE NO3. NPF-76 AND NPF-80 HOUSTON LIGHTIN6 & POWER COMPANY 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 May 2, 1995, 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 TSs 3.4.2.2. and 3.7.1.1 (Table 3.7-2) by relaxing the lift setting tolerances of the pressurizer safety valves (PSVs) from plus or minus 1% to plus or minus 2% and the main steam safety valves (MSSVs) from plus or minus 1% to plus or minus 3%, respectively.
In addition, a footnote would be added to require that the PSVs and MSSVs setpoint tnlerances be restored to within plus or minus 1% whenever a lift setting is determined to be outside plus or minus 1%
following valve testing.
1 2.0 BACKGROUNJ}
At STP, there are three PSVs set at 2485 psig. The four main steam lines have a total of 20 MSSVs (five per main steam line), each set at increments that range from 1285 to 1325 psig. The PSVs are Class I components, designed and manufactured to meet Section III of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code.
The MSSVs are Class 2 components, designed and manufactured to meet Section III of the ASME Code.
Currently, testing for the PSVs and the MSSVs is performed in accordance with ASME Section XI, every refueling outage, to assure a tolerance of plus or minus 1% of the valve setpoint.
This proposal will relax the "as found" lift settings for operable PSVs from plus or minus 1% to plus or minus 2% and for operable MSSVs from plus or minus 1% to plus or minus 3%.
This relaxation is applicable for drift of PSV and 9507280200 950725 PDR ADOCK 05000498 P
- l MSSV lift settings which occur during the operating cycle. The PSVs and MSSVs setpoint tolerances will be restored to plus or minus 1% whenever it is determined (i.e., by testing per TS 4.0.5) to be outside plus or minus 1%.
3.0 DISCUSSION On May 27, 1994, the NRC staff approved TS changes proposed by the licensee on May 27, 1993, regarding the transition to the Vantage 5 Hybrid fuel design.
The licensee's safety evaluation included mechanical, nuclear, thermal and hydraulic, and accident conditions. As part of this analysis, use of a plus or minus 2% PSV and a plus or minus 3% MSSV valves setpoint tolerance was examined.
In addition, the licensee's safety evaluation portion of the May 2, 1995, application specifically examines the impact of increased PSV and MSSV setpoint tolerance on the safety analysis. The licensee summarizes this impact as follows The analysis for the non-LOCA [ loss-of-coolant accident] safety analysis performed for the Vantage 5 Hybrid fuel upgrade amendment considered the effects of an increased tolerance for the PSVs and MSSVs.
The transients which primarily examine peak reactor coolant system pressure include the loss of load / turbine trip event (Update Final Safety Analysis Report Sections 15.2.2 and 15.3.3).
In this event the effects of the increased PSV tolerance was explicitly modeled. The results of these analyses and the evaluations of the remaining non-LOCA transients demonstrate that the PSVs will provide sufficient relief even when an analytical tolerance totalling plus or minus 2% is assumed.
The transients which examine secondary pressure are the loss of normal feedwater/ loss of offsite power event.
In this event the effects of the increased MSSV tolerance was explicitly modeled.
In addition the analysis took credit for the staggered pressure setpoints currently in the TSs. The results of the analysis demonstrated that the MSSVs will i
provide sufficient relief to keep secondary pressure below 110% of the steam generator shell design pressure even when an analytical tolerance tot.iling plus 3% is added to the relief pressure setpoint.
The staff also requested that the licensee supplement the above discussion to expand on some of the details of their analyses. The licensee provided the following additional information to the staff. The decrease from minus 1% to minus 2% will result in an approximate minimum pressure of 2435 psig. This is well above both the reactor trip setpoint of 2380 psig and the pressurizer power-operated relief valve (PORV) setpoint of 2335.
The pressurizer PORV is assumed to open during the departure from nucleate boiling (DNB) accident analysis since this will provide the worst case situation. The request to decrease the MSSV as found setpoint tolerance value from minus 1% to minus 3%
is consistent with the safety analysis and normal plant operating conditions.
The decrease from minus 1% to minus 3% will result in an approximate minimum pressure of 1246 psig, which is well above the normal maximum hot zero power operating pressure of approximately 1200 psig. Therefore, these changes will not impact the safe operation of STP.
1
. 4.0 EVALUATION The licensee has determined that the proposed TS changes do not result in a significant reduction in the margin of safety. The limiting transient in each category has been analyzed to determine the effect of the change in the setpoint tolerances. The licensee determined that the results of these analyses meet all acceptance criteria and demonstrate that the peak pressures in the primary and secondary systems do not exceed 110% of the system design pressures in accordance with the ASME Code.
Further, in order to prevent the setpoints from drifting outside the plus or minus 2% range for the PSVs and the plus or minus 3% range for the MSSVs, the licensee will continue to require both PSV and MSSV setpoint tolerances to be restored to plus or minus 1% when the as-found lift setting exceeds plus or minus 1% prior to declaring the PSVs and MSSVs operable.
This will prevent excessive setpoint drift that would cause the peak system pressures to exceed the allowable limits.
Based on the above evaluation, the staff finds that the proposed TS changes are acceptable.
5.0 STATE CONSULTATION
In accordance with the Commisrion'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 (60 FR 29877). 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.
s
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 amendments will not be inimical to the common j
defense and security or to the health and safety of the public.
j Principal Contributor:
T. Alexion j
Date: July 25, 1995 l