ML20079Q093
| ML20079Q093 | |
| Person / Time | |
|---|---|
| Site: | LaSalle  |
| Issue date: | 10/08/1991 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20079Q087 | List: |
| References | |
| NUDOCS 9111150183 | |
| Download: ML20079Q093 (5) | |
Text
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO. 79 TO FACILITY OPERATING LICENSE NO. NPF-11 AND AMENDMENT NO. 63 TO FAtiLITY OPERATING LICENSE NO. NPF-18 COMMONWEALTH EDISON COMFANY LASALLE COUNTYJTATION. UNITS 1AND2 DOCKET NOS. 50-373 AND 50-374
1.0 INTRODUCTION
Commonwealth Edison Company (CECO, the licensee) submitted a Technical Specification (TS) amendment request for the Anticipated Transient Without Scram-Recirculation Pump Trip (ATWS-RPT) system for LaSalle Station, Units 1 and 2.
The change is requested because the station has installed improved logic and instrumentation for the ATWS-RPT system on ilnit I and will perform the same modification on Unit 2 during the next refusling outage. The modifi-cations will accomplish two purposes.
First, the trip eystem instrumentation will be upgraced to a new analog systen. Second, the ALS-RPT logic will be
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changed to create two separate trip systems capable of tripping both recircula-tion pumps. The new trip systems will use "1-out-of-2 taken twice" logic.
The original design had two trip systems with each system utilizing a "1-out-4 talen once" logic and capable of tripping only one recirculation pump.
2.0 DISCUSciON y
Tue licensee has proposed the following changes to the ATWS-RPT system and to the TS:
1.
Upgrade the existing trip systems to new analog systems. Modify the trip logic to use "1-out-of-2 taken twice" logic, and configure the trips so that each trip system is capable of tripping both recirculation pumps (see Figure 1, attached, for schematic diagram of trip logic).
Evaluation - 10 CFR 50.62 requires that ATWS-RPT trips " perform their function in a reliable manner." The licensee's modification improves the reliability of the ATWS-RPT system in accordance with this regulation by providing redundant trip systems. Each trip system consists of two sets of "1-out-of-2" logic; cach "I out-of-2" logic consists of one level channel and one pressure channel. The "1-out-of-2 taken twice" logic is defined as one trip system. Each trip system is capable of tripping both recirculation pumps. The previous arrangement had no 9111150183 911008 PDA ADOCK 05000373 P
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. redundancy.
A failure of one trip system would prevent one of the recirculation pumps from being tripped.
The "1-out-of-2 taken twice" logic also improves reliability by reducing the possibility of spurious trips since two separate instrument channels must receive a signal in excess of its setpoint to cause a trip.
The staff finds this design accepteble.
2.
Modify the TS to reflect the changes to the ATWS-RPT system. The following TS changes are proposed:
A.
Table 3.3.4.1-1, change the minimum number of operable channels per trip system from 1 to 2 for the Reactor Vessel Low Weter Level trip function and the Reactor Vessel High Pressure trip function, j
Evaluation - Since the trip system logic now requires a minimum of twochannelsineachtripfunction(eitherpressureorlevel)to trip the pumps, the staff finds this acceptable.
B.
Delete Section 3.3.4.1.b.
This action statement allows the licensee 14 days to restore an inoperable trip system or be in STARTilP within the next B hours. The licensee has proposeu the following statements be added to replace the deleted Action Statement.
"b.
With the number of OPERABLE channels one less than required by the Minimum OPERABLE Channels per Trip System requirement for one or both trip systems, place the inoperable channel (s) in the tripped condition within I hour, c.
With the number of OPERABLE channels two or more less than required by the Minimum OPERABLE Channels per Trip System requirement for one trip system and:
1.
If the inoperable channels consist of one reactor vessel water level channel and one reactor vessel pressure channel, place both inoperable channels in.the tripped condition within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />, or, if this action will initiate a pump trip, declare trip system inoperable.
2.
If the inoperable channels include two reactor vessel water level channels or two reactor vessel pressure channels,-declare the trip system inoperable.
d.
With one trip system inoperable, restore the inoperable trip system to OPERABLE status within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> or be in at least STARTUP within the next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />, t
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. e.
With both trip systems inoperable, restore at least one trip system to OPERABLE status within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> or be in at least STARTUP within the next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />."
Evaluation - The proposed action statements are more conservative than the existing, reducing the maximum Allowed Outage Time (A0T) from 14 days to 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> (with one trip system inoperable) or be in STARTL'P within the next 6 incurs vice the existing 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br />.
Maximum A0T with both trip systems inoperable is I hour. The staff recognizes that, in the modified design, with "1 out-of-2 taken twice" logic arrangement, a single channel inoperable in one trip system will not inhibit an ATWS-RPT actuation should an ATWS event occur because of the redundant trip system.
If the same parameter (pressureorlevel)channelsareinoperableinboth trip systems, it has the potential for failing the ATWS-RPT actuation. Action b requires that inoperable channel (s) be placed in the tripped condition within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />.
The staff believes that during the one-hour period, the probability of failing two channels in a two trip system coincident with an ATWS event is very low.
Actions c and d address conditions within one trip system; there is no prnblem with respect to the " loss of function" concern because of the redundant trip syctem. Action e requires that at least one trip system be restored to OPERABLE status within I hour or be in at least STARTUP within the next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />. The steff believes that during the one-hour period plus the six hours for bringing the plant to the STARTUP mode, the probability for failing the RPT actuation coincident with an ATWS event is still very low. The pro >osed actions are consistent with the draft BWR Standard Tec1nical Specifications being implemented in the improved Technical Specification Program. The staff finds this acceptable.
C.
Table 4.3.4.1-1, amend the channel check requirement for the Reactor Vessel High Pressure trip function from "N/A" to Shiftly.
Evaluation - Generic Letter (GL) 85-06, " Quality Assurance Guidance for ATW5 Equipment That is Not Safety Related" provided the staff position on testing for non-safety related ATWS equipment. The licensee's existing TSs have arovisions for monthly channel furctional tests, but do not require a c1annel check of the Reactor Vessel High Pressure Channel because the existing ATWS-RPT System instruments do not provide any means of direct pressure indication.
The new ATW5-RPT system provides that capability. The staff finds this acceptable.
D.
Remove footnote "*" at the bottom of page 3/4 3-35 (Unit 1 only).
Evaluation - This footnote provided a waiver during Unit 1, Cycle 1 and is no longer toplicable. The staff finds this acceptable.
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. In summary, the staff concludes that the licensee's proposed modifications and TS amendment are acceptable. The new ATWS-RPT system provides a higher degree of reliability by providing redundancy in the trip systems and by using "I-out-of-2 taken twice" logic to minimire the possibility of spurious trips.
In addition, the new system adds a capability for a channel check that will be done on a shiftly basis.
The new TS LCO's are more conservative than the existing LC0's and are consistent with the draft BWR Standard Technical Specifications.
3.0 STATE CONSULTATION
in accordance with the Commission's regulations, the Illinois State official was notified of the proposed issuance of the amendments. The State official had no comments.
4.0 ENVIRONMENTAL CONSIDERATION
The amendments change a m uirement with respect to the installation or use of a facility component.w.dted within the restricted area as defined in 10 CFR Part 20. The NRC sttff has dotermined that the amendments involve no significant increase in tha 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 oce.upational radiation exposure. The Connission has previously issued a proposed finding that the amendments involve no significant hazards consideration, and there has been no public connent on suchfinding(56FR37578). 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 connection with the issuance of the amendments.
5.0 CONCLUSION
The Connission has concluded, based on the considerations discussed above, that:
(1) thert 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 Conmission's regulations, 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.
Attachment:
Figure 1, ATWS Logic Principal Contributor:
B. Siegel/R. Elliott
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Date:
October 8, 1991 l
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