ML20071K533
| ML20071K533 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 07/26/1994 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20071K531 | List: |
| References | |
| NUDOCS 9408010077 | |
| Download: ML20071K533 (3) | |
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UNITED STATES NUCLEAR REGULATORY COMMISSION iTg e
WASHINGTON, D.C. 205550001 ENCLOSURE 3 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT N0.185 TO FACILITY OPERATING LICENSE N0. DPR-77 APO AMENDMENT NO.177 TO FACILITY OPERATING LICENSE NO. DPR-79 JJNNESSEE VALLEY AUTHORITY SE000YAH NUCLEAR PLANT. UNITS 1 AND 2 DOCKET NOS. 50-327 AND 50-328
1.0 INTRODUCTION
By application dated June 17, 1993, the Tennessee Valley Authority (the licensee) proposed amendments to the Technical Specifications (TS) for Sequoyah Nuclear Plant (SQN) Units 1 and 2.
The requested changes would increase the allowable values of the intermediate-range (IR) neutron flux and source-range (SR) neutron flux reactor trip setpoints.
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2.0 BACKGROUND
The reactor overpower protection is provided by out-of-core nuclear instrumentation that consists of three discrete but overlapping levels.
These levels are SR, IR and power range (PR).
Continuous power increases require a permissive signal from the higher-range instrumentation channels before the lower-range level trips can be manually blocked by the operator.
2.1 Source Ranae Hiah Neutron Flux Trio The SR neutron flux trip circuit causes the reactor to trip when either of two independent SR channels exceed the trip setpoint and provides protection during reactor startup and shutdown.
The SR trip can be manually. bypassed when either of two IR channels reads above the P-6 permissive setpoint value; i.e., greater than or equal to 1/100,000 percent rated thermal power (RTP).
1 It is automatically reinstated when both IR channels decrease below the P-6 value.
The trip is automatically bypassed by two-of-four logic from the P-10 permissive (10 percent RTP). The SR trip can also be reinstated below P-10 by an administrative. action requiring manual actuation of two control board mounted switches.
l The SR trip setpoint is set between the P-6 setpoint and the maximum SR level (1,000,000 counts per second [ CPS]).
The SR trip setpoint is equal to or less than 100,000 CPS with an allowable value of equal to or less than 130,000 CPS.
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t 2.2 Intermediate Ranae Hiah Neutron Flux Trio The IR neutron flux trip circuit trips the reactor when either of two independent IR channels exceed the trip setpoint and provides protection during reactor startup. The IR trip can be blocked if two of four PR channels are above the P-10 permissive.
Three-of-four PR channels below this value automatically reinstates the trip.
The IR trip setpoint is equal to or less than 25 percent of RTP with an allowable value of equal to or less than 30 percent of RTP.
3.0 EVALUATION The licensee has requested an amendment to change the allowable values of both
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the SR and IR reactor trips in the TS Table 2.2-1, Items 5 and 6.
The SR trip setpoint remains equal to or less than 100,000 CPS, while the allowable value would be changed from equal to or less than 130,000 CPS, to equal or less than
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145,000 CPS.
The IR trip setpoint remains at equal to or less than 25 percent RTP while the allowable value would be changed from equal to or less than 30 percent RTP, to equal to or less than 45.20 percent RTP.
The licensee has requested that the allowable values for neutron flux trip be increased because new detectors have been installed that have a wider detection range of ten-decades as compared to the eight-decade range of the original detectors.
The new detectors are Gamma Metrics and were installed during the cycle 4 refueling outage to replace the original Westinghouse Electric Corporation detectors.
The new detectors were installed to meet environmental qualification requirements for accident monitoring instrumentation.
The increase in range of the new-detectors has resulted in a slight decrease in accuracy because the instrumentation errors are applied to
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a larger span, thus necessitating an increase in the allowable TS values to account for the decrease in accuracy.
t The licensee has reevaluated the accuracies for the IR and SR channels using a more conservative technique.
This technique uses a summing of loop component inaccuracies (the square root of the sum of each accuracy squared).
The staff finds this method appropriate for establishing the margin between the setooint i
2 and allowable value.
Based on our review of TVA's proposal to amend SQN's TS to increase the SR and IR allowable values for trip of the reactor on neutron flux, the staff concludes that an appropriate method was used to establish the operating i
margin based on the instrument accuracy.
Therefore, the proposed change is acceptable.
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4.0 STATE CONSULTATION
In accordance with the Commission's regulations, the Tennessee State official was notified of the proposed issuance of the amendments.
The State official j
had no comments.
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5.0 ENVIRONMENTAL CONSIDERATION
The amendments 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 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 i
exposure. The Commission has previously issued a proposed finding that the l
amendments involve no significant hazards consideration, and there has been no public comment on such finding (58 FR 41514). 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 i
environmental assessment need be prepared in connection with the issuance of the amendments.
6.0 CONCLUSIQU 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, i
and (3) the issuance of the amendments will not be inimical to the common defense and security or to the health and safety of the public.
Principal Contributor: Frederick P. Paulitz Dated: July 26, 1994 i
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