ML20077B908
| ML20077B908 | |
| Person / Time | |
|---|---|
| Site: | Dresden  |
| Issue date: | 07/21/1983 |
| From: | Purple R Office of Nuclear Reactor Regulation |
| To: | COMMONWEALTH EDISON CO. |
| Shared Package | |
| ML20077B910 | List: |
| References | |
| LSO5-83-07-037, LSO5-83-7-37, NUDOCS 8307250484 | |
| Download: ML20077B908 (4) | |
Text
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7590-01 UNITED STATES NUCLEAR REGULATORY COMMISSION In the Matter of COMM04lEALTH EDIS0N COMPANY Docket No. 50-237
)
(Dresden Nuclear Power Station,
)
Unit No. 2)
)
EXEMPTION
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Commonwealth Edison Company (CECO)(the licensee) is the holder of a Provisional Operating License No. DPR-19 which authorizes operating of the Dresden Nuclear Power Station, Unit No. 2 (the facility).
This 1.icense provides, among other things, that th.e facility is. subject to all rules, regulations and Orders of the Nuclear Regulatory Commission (the Commission) now or hereafter in effect.
The facility is a boiling water reactor located at the licensee's site in Grundy County, Illinois.
i 11, By letter dated July 20, 1983, the Commonwealth Edison Company (CECO) requested an exemption from the requirements of Appendix J,10 CFR 50, so that a Type A leak' test of the Dresden Unit 2 containment need not be redone until the next scheduled test.
The re-test is required by Section IV A of Appendix J to 10 CFR 50 because a major repair had been made to a leak in the containment boundary.
Since it is not possible to perform a local leak test at this location, a t
8307250484 830721 PDR ADOCK 05000237 P
7590-01
. Type A test which involves pressurization of the entire containment would be requi red. The leak was through a 1/8 X IIl6 inch hole in a bellows located between the drywell wall and a vacuum breaker.
The hole was inadvertently
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produced during some welding work nearby on J,ul'y 19, 1983.. The predicted leak rate from the hole at the design basis accident pressure of 48 psig was calculated to be 6.9 scfm.
The recent Type A test completed under the design basis accident pressure showed a measured containment integrated leak rate of 4.94 scfm.
The additional leak rate introduced by the new hole would result in a total leak rate, at the design basis accident peessure, of 11.84 scfm which is less than the allowable limit of 13.7 scfm used for the design basis accident calculations.
The staff ' finds the calculated leak rate from this hole to be reasonable.
Although no limiting condition for operation was being exceeded, the unit was shutdown and the leak was repaired by welding and satisfactorily leak tested at a low pressure.
Information concerning the effectOf the above repair on the bellows was furnished by CECO to the staff by telecon on July 20, 1983 and by letter dated July 21, 1983.
The staf f was informed that the bellows were designed to Nwithstand 2000 full displacement cycles during their lifetime.
A full displace-ment cycle is one in which the b llows moves from a resting state to full expansion capability.
These bellows have, throughout the approximate 131/2 year operating period of Dresden Unit No. 2, been subjected to only one such cycle.
In addition, although the effect of the above repair on the 6
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7590-01 lifetime of the bellows is that the number of cycles that the bellows will endure before failure drops by 96%, i.e., to 4% of original, the bellcws still can endure 80 such cycles before failure.
Based on operat.ing experience to date, the staff believes that a significant safety margin and operating lifetime still exists for the repaired bellows.
Accordingly, in view of the small leak rate that would result even if the entire weld were to fail during a design basis LOCA, i.e., offsite doses will be within the values previously analyzed and found acceptable and since the chance of failure of the bellows during the rest of this operating cycle is remote, the staff concludes that a temporary exemption from the requirements of Section IV A of Appendix J to 10 CFR :50 is justified and should be granted.,
However, because the repair has led to a considerable reduction in the "as installed" lifetime of th'e bellows, the ' staff concludes that an exemption is warranted only until the end of the next refueling outage.
At that time, the required Type A tests should be carried out in accordance with Section IV. A of A,ppendix J to 10 CFR 50.
I ll.,._
Accordingly, the Commission has determined that, pursuant to 10 CFR 50.12, this exemption is authorized by law and will not endanger life or property or the common defense and security, and is otherwise in the public interest, and hereby grants an exemption as described in Section II above from a portion of Section IV. A of Appendix J to the extent that a Type A pressure test is not required for the weld repair perfonned on the expansion bellows for vacuum breaker 2-1601-32B at Dresden Unit No. 2 on July 20, 1983.
7590 01 4
The Commission has determined that the granting of this Exemption will not result in any significant environmental impact and that pursuant to 10 CFR 51.5(d)(4) an environmental impact statement or negative' declaration
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and environmental impact appraisal need not be prepared in' connection with this action.
This Exemption is effective upon issuance.
FOR E NUCL LATORY COMMISSION
_ yt-Robert A. Purple, Deputy Director Division of Licensing Office of Nuclear Reactor Regulation Dated at Bethesda, Maryland this 21 day of July 1983.
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