ML20055D220
| ML20055D220 | |
| Person / Time | |
|---|---|
| Site: | South Texas  |
| Issue date: | 06/22/1990 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20055D219 | List: |
| References | |
| NUDOCS 9007050174 | |
| Download: ML20055D220 (3) | |
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UNITED STATES l
1 NUCLEAR REGULATORY COMMISSION e
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's wAswiNoTow. o. c. rosos SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NOS.17 AND 7 TO FACILITY OPERATING LICENSE NOS. NPF-76 AND NPF-80 HOUSTON LIGNTING & POWER COMPANY CITY PUBLIC SERVICE BOARD OF SAN ANTONIO CENTRAL POWER AND LIGNT 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 October 25, 1989 (ST-HL-AE-3078), 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 the South Texas Project, Units 1 and 2.
The proposed changes would change Notes 3 and 6 of Table'4.3-1 (Reactor Trip System Instrumentation Surveillance Requirements) as they apply to Functional Unit 2a, High Setpoint.
The surveillance intervals, monthly and quarterly, would be defined in terms of effective full power days (EFPD) rather than calendar days.
- 2. 0 DISCUSSION Table 4.3-1, Functional Unit 2a, High Setpoint requires various channel calibra-tions daily, monthly, quarterly, and once per 18 months.
Note 3, which addresses the monthly surveillance, requires a single point comparison of incore to excore axial flux difference when the unit is above 15% of rated thermal power. The licensee has been interpreting the note to mean that a single point comparison-is required af ter every 31 calendar days of operation above 15% power.
If the unit goes below 15% during a 31 day surveillance interval, the period is not counted as part of the 31 days.
Note 6, which addresses the quarterly surveillance has been interpreted to mean that after every 92 calendar days of operation above 75%, a calibration is required.
If-the unit goes below 75% during a surveillance interval, this period of time is not counted in the 92 day period.
The licensee has proposed using EFPD in both Notes 3 and 6 rather than calendar days, t
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3.0 EVALUATION l
The purpose of the incore/excore comparisons is to assure that the excore detectors are accurately representing the flux of the core during its lifetime i
because, among other functions, they provide input to reactor trip instruments.
The excore detectors are in a fixed location on the outside of the core.
The quantity of neutrons detected by the excore detectors is proportional to reactor power and will change as the flux profile changes, which in turn changes with core burnup.
Since the excore detectors are in fixed positions, the output will change with the flux profile.
That determines the need for the comparisons with the incore detectors.
However, because changes in the flux profile depend on core burnup, EFPDs are more representative of burning than are calendar days.
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The Power Range High Neutron Flux Reactor Trip (High Setting) is actuated when two out of four power range channels indicate a power level above a preset setpoint.
The Power Range High Neutron Flux Reactor Trip is actuated by the output of the excore detectors.
The setpoint on the Power Range High Neutron Flux Reactor Trip (High Setting) was not changed with this proposal.
The change in the single point comparison and calibration will allow these surveillances to be performed on a basis that it is representative of core burnup and flux distribution.
The ion chambers (excore detectors) that provide input to the Power Range High Neutron Flux Trip (high setpoint) also provide input to the Power Range High Positive Neutron Flux Rate Trip and the Power Range High Negative Neutron Flux Rate Trip.
These trips are not affected by the proposed change because they trip on rate of signal increase or decrease.
The rate of signal change is not affected because the single point comparison and calibration surveillances do not change the rate of signal change setpoints.
The Overtemperature and Overpower delta T trips have inputs from the excore ion chambers.
These inputs use the difference between top and bottom detector of the power range ion chambers.
The trip setpoints for the Overtemperature and Overpower delta T trips are not changed.
As with any instrument loop, the excore neutron detectors do experience instrument drift.
However, the effect of the flux profile change is much greater than the effect of instrument drift.
Instrument loops affected by drift are routinely calibrated on a 18 month frequency.
In the case of the encore neutron detectors, the calibration frequency is chosen to account for the flux profile change. While it is possible'that opyration at low power l
1evels for a long period of time would allow the sintre point comparison and i
calibration to be performed infrequently, Technical Specification 4.3-1, Functional Unit 2a, requires a comparison of calorimetric to excore power indication above 15% rated thermal power which would correct or account for most of the effects of drift.
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SUMMARY
The staff has reviewed the proposed changes and concluded that because the surveillance and inc. ore /excore comparisons are required because of fuel burnup, surveillance intervals based on EFPDs are acceptable.
Further, the setpoints for the various trips are not affected by the, proposed changes.
5.0 ENVIRONMENTAL CONSIDERATION
The amendments involve a change in a requirement with respect to the installation or use of a facility component located within the restricted area as defined in 10 CFR Part 20 and changes in surveillance requirements.
The 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 exposures.
The Commission has previously issued a proposed finding that the amendments l
l involve no significant hazards consideration and there has been no public comment on such finding. Accordingly, the amendments meet the eligibility criteria for categorical exclusion set forth in 10 CFR Section 51.22(c)(9).
Pursuant to 10 CFR 51.22(b), no environWhntal impact statement or environ-i mental assessment need be prepared in connection with the issuance of the l
amendments.
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6.0 CONCLUSION
l Based upon its evaluation of the proposed changes to the South Texas Project, Units 1 and 2, Technical Specifications, the staff has concluded that:
(1) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, and (2) such activities will be conducted in complia?1t with the Commission's regulations and the issuance of the amendmentt L'tT1 not be inimical to the common defense and security or to the health aar safety of the public.
The staff, therefore, concludes that the proposed changes are acceptable.
Date:
June 22, 1990 Principal Contributor:
G. Dick 1
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