ML20212G785
| ML20212G785 | |
| Person / Time | |
|---|---|
| Site: | Comanche Peak  |
| Issue date: | 10/30/1997 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML20212G776 | List: |
| References | |
| NUDOCS 9711070095 | |
| Download: ML20212G785 (3) | |
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDhENT NOS. 55 AND 41 TO FACILITY OPERATING LICENSE NOS. NPF-87 AND NPF-89 TEXAS UTILITIES ELECTRIC COMPANY COMANCHE PEAK STEAM ELECTRIC STATION. UNITS 1 AND 2 DOCKET NOS. 50-445 AND 50-446
1.0 INTRODUCTION
By application dated May 16, 1997 Company (TU Electric /the licensee)(TXX-97119), Texas Utilities Electric requested changes to the Technical Specifications (Appendix A to Facility Operating License Nos. NPF-87 and NPF-89) for the Comanche Peak Steam Electric Station, Units I and 2.
The proposed changes would revise core safety limit curves and Overtemperature N-16 reactor trip setpoints based on analyses of the core configuration for CPSES Unit 2, Cycle 4.
The specific changes are to TS Figure 2.1-lb, Unit 2 Reactor Core Safety Limits and TS Table 2.2-1, " Reactor Trip System Instrumentation Trip Setpoints," Units 1 and 2.
These changes are required due to the change in core configuration for CPSES Unit 2, Cycle 4 refueling.
2.0 BACKGROUND
The core safety limits are the set of points of Thermal Power, Reactor Coolant System (RCS) pressure, and average temperature below which departure form nucleate boiling ratio (DNBR) is' no less than(1) the calculated the safety analysis limit value, or (2) the average enthalpy at the vessel exit is less than the enthalpy of saturated liquid. The significant parameters used to determine these lines include the RCS flow rate, the design nuclear enthalpy rise hot channel factor (F ), the cycle-specific reference axial power shape, u
and the cycle-specific core configuration.
To avoid exceeding the core safety limits during operation, the Overtemperature N-16 reactor trip initiates a reactor trip before the limits are exceeded, providing DNB protection from events that impact power, pressure, temperature, or axial power shape. The setpoint for the N-16 trip is continuously calculated for each loop by analog.ircuitry by solving the setpoint equation that includes the trip reset function term, f(AI).
The actual core power is measured on each loop with' an N-16 power meter and used as a comparison to the calculated trip setpoint. Should an axial power distribution occur during operation that is more severe than the reference axial power shape, the trip reset function term of the setpoint equation, reduces the trip setpoint to account for the resultant effects. The range 9711070095 971030
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. over which the Overtemperature N-16 trip setpoint is calculated is bounded by the pressurizer pressure low, the pressurizer pressur. high and the overpower reactor trip setpoints. The power / temperature range that the Overtemperature i
11-16 trip must provide DNB protection is further limited by the operation of the Main Steam Safety Valves.
3.0 EVALUATION The Cycle 4 core configuration is a mixed core consisting of 172 fuel assemblies manufactured by Siemens Power Company and 21 fuel assemblies manufactured by Westinghouse Electric Company. The licensee has reduced the number of Westinghouse fuel assemblies in Unit 2, Cycle 4 as compared to Unit 2, Cycle 3, resulting in a reduction of the mixed-core penalty. The licensee also calculated the Unit 2, Cycle 4 axial power distributions to be tore skewed toward the top half of the core than those calculated for Unit 2, Cycle 3.
Therefore, it was necessary for the licensee to change the Core Safety Limits and the Overtemperature N-16 trip setpoint to reflect the Unit 2 Cycle 4 core configuration.
The licensee indicated that they used NRC approved methodologies as stated in TS 6.9.1.6.b Items 9, 10, 11, 12, 13, and 14 to determine the new reactor core safety limit curves for Unit 2, TS figure 2.1-ib.
The resultant core safety limit curves were evaluated by NRC approved analytical methods to determine the impact on the N-16 trip setpoint calculation.
It was determined that (1) although there was a slight change to the safety analysis limit of the K coefficient, the TS value remained the same, and (2) the trip reset func[ ion f(AI) required changes due to the Unit 2, Cycle 4 axial distribution being top-skewed.
The cycle-specific changes to trip reset function were determined by NRC approved methodology and resulted in an increase in the penalty for exceeding positive Al span and the removal of the penalty for exceeding the negative Al span. The removal of negative span penalty was supported by the licensee's analysis that showed that no trip setpoint reduction was required. The revisions to the f(AI) trip reset function resulted in the following proposed changes to the Unit 2, Cycle 4 Overtemperature N-16 Trip Setpoint in TS Table 2.2-1:
- Increase the positive span of the q,-q, range from -65% and +2.5% to
-65% and +7.5%
- Elimination of the Overtemperture H-16 setpoint reduction of 1.86% for each percent the magnitude of q -q exceeds -65%
-IncreasetheOvertemperatureN-l6,setpointpenalty,froma1.65%-
reduction to a 2.00% reduction, for each percent that the magnitude of the q q exceeds +7.5% (current value +2.5%)
- Footn,te, identifying that no setpoint reduction is required for the o
negative span of the AI indication
- Note 2 for the Overtemperture N-16 Allowable Value, the maximum amount the trip setpoint is allowed to exceed the computed trip setpoint is decreased from 1.88% to 1.66%.
N
, 4 The-licensee determined that the CPSES Final Safety Analysis Report (FSAR)
Chapter 15 event most affected by the change in the Overtemperature N-16 trip setpoint is Section 15.4.2, " Rod Withdrawal at Power." The licensee reanalyzed the event using NRC approved methodologies and determined that all relevant acceptance criteria were satisfieo.
The licensee has requested to change TS Figure 2.1-lb, Unit 2 Reactor Core Safety Limits and TS Table 2.2-1, " Reactor Trip System Instrumentation Trip Setpoints," Units 1 and 2 to accommodate changes due to the designed core configuration for Unit 2. Cycle 4.
The staff has reviewed the changes and based on the use of NRC ' approved methodologies to verify that all safety criteria have been satisfied. The proposed revisions to the safety limit curves and the trip setpoints will provide assurance of DNB margin.
Therefore, the staff finds the licensee's requested changes acceptable.
4.0 STATE CONSULTATION
In accordance with the Comission's regulations, the Texas State official was notified of the proposed issuance of the amendments. - The St' ate official had no comments.
5.0 ENVIRONMENTAL CONSIDERATION
The amenoments 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 detstrained 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 Comission has previously issued a proposed finding.that the amend:nents involve no significant-hazards consideration, and there has been no public coment on such finding (63 FR:38140). Accordingly, the amendments meet 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 connecticn with the issuance of the amendments.
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6.0 CONCLUSION
.The Comission 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 Comission's regulations, and (3)'the' issuance of the amendments will not be inimical to the comon defense and security or to the health and safety of the public.
Principal Contributor:
S. Brewer, SRXB Date: October 30, 1997
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