ML20059B453
| ML20059B453 | |
| Person / Time | |
|---|---|
| Site: | Beaver Valley |
| Issue date: | 08/17/1990 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20059B451 | List: |
| References | |
| NUDOCS 9008290087 | |
| Download: ML20059B453 (4) | |
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SAFETY EVAL 61. TION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NC.' iss TO FACILITY OPERATING LICENSE NO. OPR-66 DUQUESNE LIGHT COMPANY OHIO EDISON COMFANY PENNSYLVANIA POWER COMPANY BEAVER VALLEY POWER STATION, UNIT NO. 1 DOCKET NO. 50-334 1.0 INTROD*JCTION By letter dated March 2, 1989, Snd supplemented by letter dated June 12, 1990, Duquesne Light Company (the licensee) proposed certain revisions-to the Technical Specifications to revise several Reactor Trip and Engineered Safety Features (ESF) Actuation System instrumentation trip setpoints and numerous allowable values for Beaver Valley, Unit 1.
The revision of the Reactor Protection System and ESF trip setpoints and allowable values are based _upon the.results of a re-analysis of the instrument channel-inaccuracies. This re-analysis was performed to update the Beaver Valley Unit 1 setpoint methodology to the same methodology used in determiniqg Unit 2 protection setpoints.
The trip setpoints that would be revised for Unit-1 include'the Turbine Impulse Chamber Pressure P-13 Interlock, the Refueling Water Storage Tank (RWST) Level-Low and auto QS flow reduction for safety. injection transfer from-injection to recirculation, the Containment. Pressure High-High,. Containment'-
Pressure Intermediate High-High and the Emergency Buses Undervoltage settings for Degraded Voltage.
In addition, numerous:setpoint allowable values would be revised consistent-with the calculated-inaccuracies.
The methodology used is described in detail in Westinghouse WCAP-11419
" Westinghouse Setpoint Methodology for Protection Systems, Beaver Valley Unit 1" (proprietary) and WCAP-11420.
-In addition to determining the required trip setpoints and allowable values,
.the methodology. includes an optional provision for determining the OPERABILITY of a channel when its trip setpoint is found to exceed the allowable value.
The licensee has elected not to incorporate this provision into the Unit-1 Technical Specifications for:this revision; consequently, we did not review this feature.
9008290087 900817 PDR ADOCK 05000334
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' 2.0 EVAL.UATION 2.1 Setpoint Calculation Methodolony The methodology used to combine the error components for a channel is basically the' appropriate statistical combination of those groups of components which are-statistically independent, i.e., not interactive.
Those errors which are not independent are placed arithmetica11y into groups.
The groups themselves are independent' effects and can then be systematically combined.
.The methodology used for this combination is generally the square root of the sum of the squares which has been utilized in Westinghouse reports for Beaver Valley Unit 2.
This technique, or other statistical approaches of a similar nature, have been used in WCAP-10395 and WCAP-8567. WCAP-8567 has been. approved by the NRC staff, thus, noting the acceptability of statistical techniques for the application requested. The methodology used for this report is essentially the same as that used for V.C. Summer which was approved by the NRC in NUREG-0717, Supplement No. 4.
2.2 Sensor Allowances Four parameters are considered to be sensor allowances -- Sensor Calibration Accuracy (SCA), Sensor Drift (SD), Sensor Temperature Effects (STE), and Sensor, Pressure Effects (SPE).
Of these four parameters, STE and SPE are considered to be statistically independent; SD and SCA are also statistically independent and treated as interactive which is more conservative.
STE and SPE are considered to be independent due to the manner in which the instrumentation is checked, i.e., the instrumentation is calibrated and drift determined under conditions in which pressure and temperat'?r 1tre assumed constant.
SD and SCA are considered to be interactive for i.. 5ame reason that STE and SPE are considered independent, i.e., due to the manner in which the instrumentation is checked.
Instrumentation calibration techniques use the same process for determining instrument drift, that-is, the end result of the two is the same. When calibrating a sensor, the sensor output-is checked
.to determine if it is representing accurately the input. The same is done for a determination of the sensor drift.
Thus, it is impossible to determine the differences between calibration errors'and drift when a sensor is checked for the second and subsequent times.
Based on this reasoning, SD and SCA have been added to form an independent group.
2.3 Rack Allowance Four parameters are considered to be rack allowances, Rack Calibration Accuracy (RCA), Rack Comparator Setting Accuracy-(RCSA), Rack Temperature Effects (RTE), and Rack Drift (RD).
Three of these parameters are considered to be interactive, RCA, RCSA, and RD, for much the same reason as described in 1
3-2.2 above. When calibrating or determining drift in the racks for a specific channel, the processes are performed at essentially constant temperature, i.e, ambient temperature.
Because of this, the RTE parameter is considered to be independent of any factors for calibration or drift.
As noted in 2.2, when calibrating or determining drift for a channel, the same end result is desired, that~is, at what point does the bistable change state.
After the initial calibration, it is not possible to distinguish the difference between a calibration error, rack drift or a comparator setting error.
Based on this logic, these three factors have been added to form an independent-group.
2.4 Process Allowance The Process Measurement Accuracy (PMA) and Primary Element Accuracy (PEA) parameters are considered to be independent of both sensor and rack parameters.
PMA provides allowance for the non-instrument related effects.
PEA accounts for errors due to metering devices.
2.5 Combination of Error Components The relationship between the error components and the total statistic error allowance for a channel is represented by Equation 2.1 in WCAP-11419,
" Westinghouse Setpoint Methodology for Protection Systems, Beaver Valley, Unit 1."
According to Equation 2.1, drift and calibration accuracy' allowances are interactive and thus not independent.
The environmental allowance is not necessarily considered interactive with all other parameters but it is added to the statistical sum.as an additional degree of conservatism.
The. licensee assumes that the accuracy effect on a channel due to cable degradation in an accident environment will be less than 0.1 percent of span.
This impact has been considered negligible and is not factored into the analysis.
The Westinghouse setpoint methodology results.in a value with a 95 percent probability with a high confidence level.
By letter dated June 12, 1990, the licensee stated that the confidence level is 95 percent or better.
With the exception of PMA, RD, and 50, all uncertainties assumed are the extremes of the ranges of the various parameters, i.e., are better than 2 values. Thus, the approach represented by this report is considered as conservative and
.follows-the V. C. Summer plant setpoint methodology previously approved by the NRC.
2.6 Technical Specification Change The setpoints for the various functions in the RPS and ESF Actuation System are determined on the basis of the trip settings assumed in the FSAR accident and transient analysis. The required settings correspond to the trip points assumed in these analyses less the required allowance for instrument inaccuracies.
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4 An analysis has been performed to update the calculation of these instrument inaccuracies using a more current methodology for determining the required trip setting and allowable value limits.
The methodology used is described in detail in Westinghouse WCAP-11419.
The proposed changes to Table 2.2-1 and Table 3.3-4 revise the allowable values based on the calculation of the -
iii trument inaccuracies using a more current methodology.
By using the methodology described in Westinghouse WCAP-11419, the plant gains added operational flexibility and yet remains within the analytical limit values accounted for in the various accident analysis.
In addition, the methodology. allows for a sensor drift factor and an increased rack drift
' factor.
The proposed changes to revise the allowable values in Table 2.2-1 and Table 3.3-4 of the Beaver Valley Unit 1 Technical Specifications are based on the calculation of the instrument accuracies by using approved current methodology and are acceptable.
3.0 ENVIRONMENTAL CONSIDERATION
The amendment changes 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. We have determined that the amendment involves no signif-icant 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 staff has previously issued a proposed finding that this amendment involves no significant hazards consideration and there has been no public comment on such finding.
Accordingly, this amendment meets the eligibility criteria'for categorical exclusion set forth in 10 CFR 51. m c)(9).
Pursuant to 10 CFR 51.22(b) no environmental impact statement or environmental assessment need be prepared in connection with the issuan.:.e of tnis amendment.
4.0 CONCLUSION
We have 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, and (2) such activities will be conducted in compliance with the Commission's regulations, aM (3) the issuance of this amendment will not be inimical to the common defense and security or to the health and safety of the public.
Dated: August 17, 2990 Principal Contributor:
S. Rhow
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