ML20210T007
| ML20210T007 | |
| Person / Time | |
|---|---|
| Site: | Wolf Creek  |
| Issue date: | 08/09/1999 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML20210T005 | List: |
| References | |
| NUDOCS 9908180256 | |
| Download: ML20210T007 (3) | |
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rarg UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 30006 0001
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- ews4 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO.126 TO FACILITY OPERATING LICENSE NO. NPF-42
. WOLF CREEK NUCLEAR OPERATING CORPORATION WOLF CREEK GENERATING STATION DOCKET NO. 50-482
1.0 INTRODUCTION
By application dated June 10,1999, Wolf Creek Nuclear Operating Corporation (the licensee) requested changes to the Technical Specifications (TSs, Appendix A to Facility Operating License No. NPF-42) for the Wolf Creek Generating Station (WCGS). The proposed changes would revise Technical Specification Table 3.3-4, Functional Unit 7.b., Automatic Switchover to Containment Sump (Refueling Water Storage Tank Level - Low-Low) to reflect the results of calculations that were performed for the associated instrumentation setpoints to consider the density variations due to temperature and boric acid concentrations. The licensee did not submit any changes to the Bases of TSs.
The proposed changes are to both the current TSs and ths improved TSs. The improved TSs were approved in Amendment No.123, issued March 31,1999, but have not yet been implemented. The improved TSs are to be implemented by December 31,1999.
2.0 EVALUATION The refueling water storage tank (RWST) supplies borated water to both trains of the emergency core cooling water system (ECCS) and the containment spray system through a common suction line to each system's supply header during the injection phase of a loss of coolant accident (LOCA). At the end of the injection phase of a LOCA, the source of water is automatically switched to the containment recirculation sumps. The recirculation mode is entered when the level in the RWST reaches the RWST Low-Low 1 automatic transfer signal coincident with a safety injection signal. Switchover from the RWST to the containment sumps must occur before the RWST empties to prevent damage to the ECCS pumps, and must not occur before there is sufficient water in the containment sumps to support ECCS pump operation.-
To accomplish the' automatic switchover, the RWST is equipped with four safety-related level transmitters, which feed five bistables that provide indication of a range of levels in the RWST (e.g., Hi, Low, Low-Low 1, Low-Low 2, and Empty). The RWST Low-Low 1 allowable value/ trip
- setpoint is selected to ensure adequate water remains in ths RWST to complete the switchover to the containment sumps.
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.- The current RWST Low Low 1 setpoint is greater than or equal to 36 percent of instrument span with an allowable value of greater than or equal to 35.1 percent of instrument span. Both include consideration for instrument uncertainty. However, the RWST instrument loop uncertainty calculation associated with the current TS values did not consider the density variations due to temperature and boric acid concentration. Specifically, the four RWST level transmitters are calibrated with water at t reference temperature of 68'F. With this calibration methodology, two components of error are introduced: (1) water density due to a change in temperature, and (2) bias error in the transmitter span for the differences between the density of the boric acid concentration in the RWST and the density of the water used for calibration at the same temperature.
A revised calculation of the RWST level instrument uncertainty and TS values was performed in accordance with Topical Report 89-001, "WCNOC Nuclear Safety Analysis Setpoint Methodology for the Reactor Protection System." As a result of the new calculation, it was determined that the RWST level instrumentation allowable value should be increased from 35.1 percent of instrument span to 35.5 percent of instrument span. The allowable value increase is more restrictive than the current value, which results in the allowable value being the same as the calibration tolerance band. However, this is acceptable since the measurement error (e.g.,
instrument drift) has been insignificant during the surveillance interval and the quarterly analog channel operational tests have demonstrated that the instrumentation has remained well within
' the calibration tolerance band.
i in addition to a change in the allowable value, the revised calculation resulted in changes to terms used to ensure the total allowance value (e.g., the difference between the safety analysis limit and the nominal trip setpoint) is not exceeded. Specifically, the "Z" term (e.g., the square root of the sum of the squares of those terms for which there is no periodic surveillance) changed from 1.21 to 1.65, and the "S" term (e.g., the sensor error in TS Table 3.3-4) changed from 1.86 to 1.82.
The changes to the "Z" and "S" terms and the allowable value do not impact the ECCS injection volume. Further, the safety analysis limit and nominal trip setpoints are not affected when accounting for the density variations due to temperature and boric acid concentrations.
Therefore, adequate water remains in the RWST following receipt of the RWST Level Low-Low 1 signal to complete switchover of the ECCS pumps for recirculation. Additionally, the changes to the "Z" and "S" terms and the allowable value have no impact on containment spray system operation. Other RWST level setpoints exist to ensure a timely switchover of the containment spray pumps to the containment sumps as a suction source.
The proposed changes impose a more restrictive allowable value for the RWST Low-Low 1 switchover setpoint than currently exists in the WCGS TS and are consistent with the revised uncertainty calculation. Based on the above, the proposed changes'are acceptable.
3.0 STATE CONSULTATION
in accordance with the Commission's regulations, the Kansas State Official was notified of the proposed issuance of the amendment. The State official had no comments.
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4.0 ENVIRONMENTAL CONSIDERATION
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 involves 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 amendment involves no significant hazards consideration, and there has been no public comment on such finding (64 FR 35215). _ 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 amendment.
5.0 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.
- PrincipalContributor: K. Thomas Date:. August 9, 1999 1}'