ML20247C340
| ML20247C340 | |
| Person / Time | |
|---|---|
| Site: | Point Beach  |
| Issue date: | 05/18/1989 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20247C336 | List: |
| References | |
| NUDOCS 8905240409 | |
| Download: ML20247C340 (3) | |
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UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON D. C. 20$55
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-3 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NOS.121 AND 124 TO FACILITY OPERATING LICENSE N05. DPR-24 AND DPR-27 WISCONSIN ELECTRIC POWER COMPANY POINT BEACH NUCLEAR PLANT, UNIT NOS. 1 AND 2 DOCKET NOS. 50-266 AND 50-301 INTRODUCTION By letter dated January 6,1987, Wisconsin Electric Power Company, the licensee for Point Beach Units 1 and 2 proposed a change to the plants' Technical Speci-fication Table 15.4.1-1 to increase the period of the logic channel test of the reactor trip resulting from low reactor coulant flow being simultaneously detected in both reactor coolant loops. Specifically, the frequency of logic channel testing for this condition is changed from monthly to each (annual) refueling outage. Supplemental information related to the January 6 letter was provided in a May 15, 1987, letter from the licensee in response to a staff request for additional information. A clarification to the proposed change was made by the licensee in a letter dated April 14, 1987.
EVALUATION To protect the core from departure from nucleate boiling (DNB) due to a los:;
of adequate reactor coolant flow, the Point Beach Units 1 and 2 protection systems include a reactor trip initiated by low reactor coolant flow signals in each reactor coolant loop. Low flow in both loops initiates a reactor tri when the plant is above approximately 10% power (the P-7 interlock setpoint) p but less than 50% power. Above approximately 50% power (the P-8 interlock setpoint), low flow in any reactor coolant loop initiates the reactor trip.
To develop the signals for the low reactor coolant flow reactor trip, three flow sensing channels are installed in each loop.
Each of the instrument channels consists of a flow sensor which provides an input to a bistable. On a low flow condition, the bistable de-energizes a corresponding relay in each of the two protection logic trains. Within each logic train, contacts from the three corresponding relays are combined in two-out-of-three logic to de-energize two parallel relays. Above P-8, the reactor will trip when both parallel relays in either loop de-energize. Above P-7 but below P-8, the reactor will only trip when the parallel relays in both loops de-energize.
i Currently, under Functional Unit 5 in Table 15.4.1-1 of the plants' Technical Specifications, a monthly logic channel test of the above relays / contacts which initiate the reactor trip on low reactor coolant flow is required.
8905240409 890518 PDR ADOCK 05000266 P
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The circuitry (test switches, etc.) used to perform the logic channel test of the relays / contacts was designed to only test the parallel relays associated with one loop at a time. Because of this design, a test of the contacts from the parallei relays which initiate a trip on simultaneous low flow in both loops cannot be performed unless bistables are placed in the trip conditions.
Since bistable outputs are shared by both logic trains, this ultimately would lead to a reactor trip since only one reactor trip bypass breaker can be used at a time. Based on this, the licensee has requested that the surveillance interval for the channel logic associated with low flow in both loops be increased from monthly to each refueling outage. The surveillance interval for the logic channel test of the relays / contacts which initiate the trip on low reactor coolant flow in any loop will remain monthly.
Since all bistables and relay coils will still be tested monthly, the net effect of the proposed technical specification change would be to increase the risk due to the increased interval (each refueling outage versus monthly) during which operability of the specific relay contacts which initiate the trip on simultaneous low flow in both loops is not demonstrated. Although a numerical quantification of the increase in risk has not been performed, the staff concludes that it would be quite small since the event of concern would require two contact failures (one in each train) between refueling cycles and a loss of flow condition occurring while the reactor is between 10% and 50%
power which is, according to the licensee, a rare occurrence.
Furthermore, the most likely cause for loss of flow in both reactor coolant loops is due to electrical failure.
If the reactor trip on loss of flow in both loops were to fail between 10% and 50% power, backup trips on underfrequency and under-voltage remain in effect. Simultaneous loss of flow in both loops due to broken coolant pump shafts or locked-rotor accidents are considered incredible events. Based on this, the staff concludes that a circuit modification to allow at-power testing of the relay contacts which trip the reactor on simultaneous low flow in both loops is not warranted and that the requested technical specification is acceptable.
ENVIRONMENTAL CONSIDERATION These amendments involve a change in the installation or use of facility component located within the restricted area as defined in 10 CFR Part 20 or changes an inspection or surveillance requirement. The staff has determined that the amendments involve no significant increase in the amounts, and no significant change in the types, of any effluer.ts that may be released off site, and that there is no sie ificant increase in individual or cumulative occupa-n tional radiation exposure. The Commission has previously published a proposed finding that these amendments involve no significant hazards consideration and there has been no public comment on such finding. Accordingly, these amendments meet the eligibility criteria for categorical exclusion set forth in 10 CFR 951.22(c)(9). Fursuantto10CFR51.22(b),noenvironmentalimpactstatement or environmental assessmat need be prepared in connection with the issuance of these amendments.
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.- 74 CONCLUSION The staff 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, and (2) such activities will be conducted in compliance with the Commiesion's regulations, and 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:
Fred Burrows
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Dated:
May 18. 1989 l
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