ML20216H488
| ML20216H488 | |
| Person / Time | |
|---|---|
| Site: | Callaway  |
| Issue date: | 04/13/1998 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML20216H482 | List: |
| References | |
| NUDOCS 9804210152 | |
| Download: ML20216H488 (5) | |
Text
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UNITED STATES g
j NUCLEAR REGULATORY COMMISSION
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2 WASHINGTON, D.C. 206 4 0001 o% *****/
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l SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO.125 TO FACILITY OPERATING LICENSE NO. NPF-30 UNION ELECTRIC COMPANY CAI I AWAY PLANT. UNIT 1 DOCKET NO. 50-483 l
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1.0 INTRODUCTION
l By letter dated October 31,1997, as supplemented by letter dated February 27,1998, Union Electric Company (the licensee) requested changes to the Technical Specifications (Appendix A l
to Facility Operating License No. NPF-30) for the Callaway Plant. The proposed changes would incorporate changes to setpoints and allowable values in TS Tables 2.2-1,4.3-1 and i
3.3-4, as well as their associated Bases. The proposed amendment is required by the licensee to preclude occurrences such as repeated alarms, rod blocks, and partial reactor trips that continue to occur during routine surveillance tests, especially during the beginning of cycle i
operation following refueling outages. The licensee stated that the proposed amendment l
besides reducing the potential for distracting operator attention away from more safety significant evolutions, will also eliminate the requirement to reduce power during surveillance testing in order to avoid reactor trips, since the channel being tested is placed in a tripped l
condition.
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The February 27,1998, supplemental letter provided additional clarifying information that did not change the initial no significant hazards consideration determination that was published in the Federal Register on January 14,1998,
2.0 PROPOSED CHANGE
S AND EVALUATIONS 2.1.
Column entries for the Total Allowance (TA), Z, and S setpoint terms for the Delta T functions are deisted.
2.1.1 The affected functional units in TS Table 2.2-1 are:
Functional Unit 7 - Over temperature Delta T (OTDT),
Functional Unit 8 - Overpower Delia T (OPDT),
Functional Unit 13.a - Steam Generator (SG) Water Level Low-Low Vessel Delta T (Power-1), and Functional Unit 13.b - SG Water Level Low-Low Vessel Delta T (Power-2).
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1 2.1.2 The following affected functional units in TS Table 3.3-4 are associated with the start of the auxiliary feedwater pumps upon SG Water Level Low-Low.
I Functional Units 6.d.1).a and 6.d.2).a - Vessel Delta T (Power-1),
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Functional Units 6.d.1).b and 6.d.2).b - Vessel Delta T (Power 2).
l Evaluation In their submittal, the licensee stated that the optional Action b.1 of the current TS (CTS) 2.2.1 and 3.3.2 is not used anymore. Un il the current TS to improved TS conversion is completed, the affected functional units will apply the CTS Action b.2. Action b.2 does not rely on TA, Z and S terms for entry. Therefore, fnere is no need to retain the TA, Z, and S setpoint terms in j
the CTS since they have meaning only in the context of the setpoint calculations. The staff l
concludes that the proposed revision is, therefore, acceptable.
l 2.2 Setpoint and allowable value changes.
I 2.2.1 The nominal top setpoint (K1) for the OTDT trip function has been increased from 1.15 to 1.1950. The allowable value for the OTDT trip function has been increased by 1.93% Delta T span.
2.2.2 The nominal trip setpoint (K4) for the OPDT trip function has been increased from 1.09 to 1.1073. The allowable value for the Overpower l
Delta T trip function has been decreased by 0.03% Delta T span.
2.2.3 The nominal trip setpoints for the Vessel Delta T Power-1 and Power-2 l-portions of the SG Water Level Low-Low RTS and ESFAS trip functions I
have been increased by 2.41% of reactor thermal power (RTP).
2.2.4 Note 6 of Table 4.31 will be revised to change the word "value" to l
" values" and add words "and T," between words " Vessel Delta T" and
" values".
Evaluation l
In their submittal, the licensee stated that implementaQ 1 of the proposed TS modification will not affect assumptions of the safety analyses for any of the accidents previously evaluated, the protection systems will continue to function in a manner cont. stent with the plant design basis, and the overall protection system performance will remain within the bounds of the previously performed accident analyses.
The staff's review verified that the licensee's setpoint calculations (1) properly addressed all components of the instrument uncertainties, (2) were based on an acceptable methodology, and 3) properly addressed the margin between the TA and channel statistical allowance (CSA)
1 j so that it is not reduced significantly. Total allowance is the difference between the safety analysis limit (SAL) and the nominal trip setpoint, and the CSA is a total of the instrument channel's uncertainty.
The staff, through its request for additional information (RAI) dated January 20,1998, requested the licensee to provide copies of the referenced setpoint calculations and clarifications of the "significant hazards evaluation." The licensee in their response to the staff's RAI provided clarifications relating to the calculation methodology used to calculate the proposed setpoint values and also provided tables containing the existing and new-calculated-values of setpoints and allowable values. The staff found the licensee's setpoint calculation methodology acceptable as it properly accounts for Instrument uncertainty and margins in setpoint and allowable values.
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- heir response to the staff's RAI, the licensee stated that for the setpoint calculations, all terms of process measurement accuracy (PMA) were not eliminated, but only those terms which are relating to hot leg streaming and scoop streaming were treated using a fixed bias.
The value of this bias was not calculated but was determined by operating experience during Cycle 8, which indicated that the streaming effect was unidirectional in nature. The resistance temperature detector (RTD) sensor drift and calibration accuracy error terms were not just eliminated but were treated differently by including (1) a power calorimetric term equal to 1.33%
of delta T measurement span to account for the RTD calibration accuracy including measurement and test equipment (M&TE) terms, and (2) the additional burn down effects bias of 1.0 F for Delta T measurement and of 0.5 F for T measurement to account for the RTD o
drift and hot leg streaming effects. The licensee further stated that the above biases are in addition to periodic re-normalization of each loop's parameters performed during quarterly surveillance to compensate for the RTD uncertainties. The licensee's explanation is acceptable as it provides justification for the capability of the instrument loop to properly respond to a demand if such a demand was placed on the system during the period between the two successive surveillance (i.e. Just before the loop was to be re-normalized).
In their response to the RAI, the licensee also stated that in their past TS revisions, the PMA term for the OTDT function included an additional error component corresponding to the 2%
value in the TS Table 4.3-1 Note 3. This note stipulates that if the absolute difference between incore and excore axial flux difference (AFD) is 2 2% during the monthly surveillance, the channel must be recalibrated. The licensee believes that this PMA term was overly conservative in that the setpoint margin is always used even when the AFD penalty function from TS Table 2.2-1 Note 1 is not imposed, i.e., when the AFD is within the deadband where no trip setpoint penalty is imposed. TI'is PMA error component will no longer be treated as a random term in the CSA; rather, it will be applied as a bias only when the AFD is outside the deadband. AFD deadband is the band where the value of the setpoint penalty for the AFD function is taken as zero. The licensee justified elimination of the random PMA error component by moving the AFD penalty function deadband la by a corresponding 2% on both sides. Moving the deadband in by 2% shortens the deadband or requires the setpoint penalty to bs taken sooner which is conservative. This is acceptable to the staff.
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in their submittal, the licensee stated that the new setpoint calculation resulted in a reduced l
value of the rack drift error component as compared to what was previously assumed. Plant i
data supports this reduction. Also, the seismic allowance bias from the OTDT setpoint calculation was eliminated from the revised calculation. The seismic allowance was originally included by Westinghouse as a result of minor setpoint shifts in the Westinghouse 7300 Process Protection System NCH (Function Generator) and NPC (Potentiometer) cards obseNed during seismic qualification testing. However, the OTDT trip function is not required to provide plant protection coincident with any seismic events. Westinghouse had previously included this bias to account for the following sequence of events: (1) a less than an operating basis earthquake occurs for which no plant shutdown is required, (2) the potentiometer of the AFD penalty function card shifts introducing an additional unknown error in the instrument loop and, (3) with this potentiometer shift present, a subsequent plant transient occurs that requires OTDT protection. To support the elimination of the seismic bias and to protect agairist the sequence of events described above, the licensee revised the plant seismic response procedures for responding to any ground motion sufficient to actuate the seismic annunciators
(> 0.01g). These revised procedures require a specific evaluation of the impact of ground 4
motion on the AFD penalty function cards, to ensure that seismic-induced errors are not introduced. This is acceptable to the staff as it provides the necessary response to ensure proper instrument function following a seismic event.
2.3 Revise associated Bases sections, Tables, Notes and Surveillances to reflect the revised trip setpoints and revised allowable values.
Evaluation The licensee's proposed modifications to the Bases, Notes and Surveillance requirements are consistent with the proposed setpoint and allowable value changes in the TS and are, therefore, acceptable to the staff.
3.0 STATE CONSULTATION
3 In accordance with the Commission's regulations, the Missouri State Official was notified of the proposed issuance of the amendment. The State official had no comments.
4.0 ENVIRONMENTAL CONSIDERATION
The amendment changes a requirement with respect to installation or use of a facility l
component located within the restricted area as defined in 10 CFR Part 20 and changes surveillance requirements. 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 I
occupational radiation exposure. The Commission has previously issued a proposed finding l
l that the amendment involves no significant hazards consideration, and there has been no l
public comment on such finding (63 FR 2283). Accordingly, the amendment meets the l
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, 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, Principal Contributor: S. V. Athavale
- Date:
April 13, 1998 4
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