ML20031D199
| ML20031D199 | |
| Person / Time | |
|---|---|
| Site: | Zion File:ZionSolutions icon.png |
| Issue date: | 09/25/1981 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20031D192 | List: |
| References | |
| NUDOCS 8110130082 | |
| Download: ML20031D199 (4) | |
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR PIGULATION RELATED TO AMENDMENT NO. 6g TO FACILITY OPERATING LICENSE NO. DPR-39 COMMONWEALTH EDISON COMPANY ZION STATION UNIT 1 DOCKET NO. 50-295
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Introduction By telecopied letter dated September 25, 1981, the Commonwealth Edison Company (the licensee) requested a change to the Technical Specifications,
appended to Facility Operating License DPR-39 for Zion Station, Unit No.1.
The proposed change would add the following temporary provision to item 3.15.1.C.1, Reserve AC Offsite Power, Unit No.1:
. In lieu of 345 kv bus section 3, the Unit 2 system auxiliary trans-forner (TR242), and the switchgear necessary to supply the Unit 1 4160 volt buses 147,148 and 149, for the period of September 25, 1981, through October 2,1981, the reserve access to offsite powlfr for Unit 1 shall be operable and placed in cperation within 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> by removing the Unit 1 generator disconnect links and backfeeding power through the Unit 1 main transformers to the Unit 1 auxiliary transformer (TR141) and the Unit 14160 volt buses 147, 148 and 149.
Background
The Zion plant staff have detected a high hydrogen level in Unit 2 system auxiliary transformer (TR 242), apparently due to breakdown of the insulating oil. Another transformer of this type elsewhere in the Coninonwe'alth Edison generating system exhibited the same symptoms just prior to catastrophic failure of the transformer. The plant staff would like to take the Zion transformer out-of-service to drain the oil and inspect the transformer prior to a failure.
l The transformer TR 242 serves two safety-related functions: it provides ininediate access to offsite power for Unit No. 2 and it provides the pntsent reserve access to offsite power for Unit No.1.
Unit No. 2 is not operating, but is in refueling. Unit No.1 is operating at full power. The Technical Specifications for Unit No.1 allow operation for only 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> in the event
'8110130082 810925 gDRADOCK05000
. the neserve access line from Unit No. 2 is not available. The planned mainte-nance for TR 242 is expected to require at least 4 days and, if significant defects are found during the inspection, the necessary repairs could take r!. I about 3 weeks additional.
Evaluation i
The design of each Unit at the Zion station includes three access routes to the offsite power available in the switchyard:
(1) On plant trip, the auxiliary loads (both ESF and plant loads) are fast transferred to the unit's startup transformer (" System Auxiliary Transfonner," TR 142 or TR 242). This is an inanediate access to the offsite power.
(2) If the startup transfonner cannot provide the necessary power, the ESF loads can be manually transferred within 20 minutes ato a reserve feed from the startup transfonner of the opposite Unit - a slightly delayed access.
(3) Power can be obtained by opening the Unit's generator disconnect links and backfeeding the offsite power through the Unit's main transfonner to the Unit's auxiliary trans-fonner (TR 141 or TR 241) - a " delayed" access to offsite power.
When NRR staff first became aware of this situation at the Zion station (September 23,1981), Coninonwealth Edison was considering providing temporary connections between Unit 1 and Unit 2 in lieu of the second access required by th~e Technical Specifications that would not be available when the transformer TR 242 is taken out of service. After discussing the matter, the licensee agreed that the use of the delayed access was a more satisfactory temporary solution.
The auxiliary loads for Unit No. 2 were being provided power via its startup transfonner (TR 242). Due to the imminent possibility of loss of this source of powdr, the licensee agreed to immediately implement their plans to open the Unit generator disconnect links and to provide power to the plant loads via the Unit's auxiliary transfonner by bpckfeeding the main transfonner -
i.e., put the delayed access into operation. This change over was accomplished the night of September 23, 1981. This configuration provides another level of redundancy. We expect the licensee to continue providing power to Unit No.1 in this manner until all necessary maintenance actions on TR 242 ant satisfac-torily complete.
Since Unit No. 2 is already shutdown and could find itself drawing offsite power from the Unit No.1 startup transforner and Unit No.1 could trip and need to draw powe'r also from the same startup transformer, we raised the question of the capacity of this transformer. The Zion staff has stated that they have re-reviewed the loads that could occur on this transfonner (both ESF loads and all other transferred loads) against the transfonner capacity. They have concluded that the transfonner can provide these loads indefinitely, i.e., without entering int, any short-term ratings.
. i Unit No.1 presently has three accesses to offsite powe'r; when TR 242 is taken out of service, two of these accesses will remain available. The first access (the Unit's startup transformer) is immediately available and adequately covered by the Technical Specifications. The second access (backfeeding the main trans-former) is a delayed access that could be in operation in 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> if needed, but is not mentf 6ned in the Technical Specifications. The plant design exceeds the requirements of General Design Criterion 17, which requires a minimum of two accesses to offsite power. GDC-17 requires that only one of these accesses be available immediately. Therefore, even with transformer 242 out-of-service, the design appears to satisfy 30C-17.
We asked the licensee to re-review the original licensing documents to determine if any reason could be found that would indicate that safety credit could not be given for the delayed access. The licensee's review found no such reason.
Our review of the licensing documents did not uncover any reason why credit could not be given for a temporary change.
We expect that if Unit No.1 should trip and need to obtain power from the onsite diesel generators, that the delayed access toute will be put into opera-tion as soon as possible. Therefore, wit'hin 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> the auxiliary loads would be operating ag&in on offsite power, which is the " preferred source," and re'11ance on the diesels can be reduced to standby protection.
In the event that major repair action is required for transformer 242, this evaluation would support an extension of this temporary change for a one-time 30-day period.
Sunnary In summary, we find that, due to the design capabilities of the Zion Station, Unit No.1, the use of the delayed acceskto offsite power can be used temoo-rarily in lieu of the reserve feed from the other Unit. Since this design will satisfy GDC-17 and our other safety concerns, we find the Technical Specification change to be acceptable.
Environmental Consideration We have determined that the amendment does not authorize a change in effluent types or total amounts nor an increase in power level and will not result in any significant enviornmental impact. Having made this determination, we have further concluded that the amendment involves an action which is insignificant from the standpoint of environmental impact and, pursuant.to 10 CFR 551.l(d)(4),
that an environmental impact statement or negative declaration and environmental impact appraisal need not be prepared in connection with the issuance of this amendment.
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. Conclusion-We have concluded, based on the considerations discussed above, that:
(1) because the amendment does not involve a significant increase in the probability or consequences of accidents previously considered and does not involve a signi-cant hazards consideration, (2) gin, the amendment does not involve a signifi-ficant decrease in a safety mar there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, and (3) such activities will be conducted in compliance with the
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Commission's regulations and the issuance of this amendment will not be inimical
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to the common defense and security or to the health and safety of the public.
Date:
September 25,1981 O
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