ML20084K698
| ML20084K698 | |
| Person / Time | |
|---|---|
| Site: | Dresden, Quad Cities, 05000000 |
| Issue date: | 10/21/1974 |
| From: | Abel J COMMONWEALTH EDISON CO. |
| To: | Case E US ATOMIC ENERGY COMMISSION (AEC) |
| Shared Package | |
| ML20084K638 | List: |
| References | |
| NUDOCS 8305190519 | |
| Download: ML20084K698 (3) | |
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Address Reply to: Post Office Box 767 CNeago, Illinois 60690
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[U October 21, 1974 b ;00T'23W*" N g
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..... v. c a n 17 * % ' 4,w Mr. Edson G. Case
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Acting Director
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20545
Subject:
Dresden Station Unit 2 and Quad-Cities Station Unit 2 Reactor Water Recirculation 4-Inch Diameter Piping Crack Investigation Program, AEC Dkts 50-.237 and 50-265,
Dear Mr. Case:
Since the discovery of a;through wall crack in the 4-inch diameter reactor water recirculation B pump discharge valve bypass piping at Dresden Station Unit 2 on September 13, 1974, an investi-gation'to determine the cause of the cracks has been in progress.
An interim report of the results to-dato of this investigation was discussed with merriners of your staff in a meeting on October 3, 1974.
In brief summary, the results to-date were t.he following.
Interim Status Specimens of the cracked piping from Dresden Unit 2 "B-Loop" and Quad-Cities Unit 2 were examined metallurgically at Argonne National Laboratory and at General Electric Company's Vallecitos Laboratory.
These examinations indicated that these two cracks were cauced by stress assisted corrosion originating on the pipe inside surface.
ASME Code stress calculations, finite element stress cal-culations, and a dynamic analyses have indicated there are no unusual stresses or vibrations.
To-date, vibration monitoring instrumen %.1 7 at Quad-Cities Unit 2 has indicated no excessive vibratior.
It has been determined from quality control records that the 4-inch diameter bypass piping at Dresden Unit 2, Quad-Cities Unit 2, and Millstone Unit 1 was obtained from a single heat of steel.
The Dresden Unit 3 and Quad-Cities Unit 1 4-inch diameter 8305190519 741216 s7).9M, O I PDR ADOCK 05000237 S
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Mr. Edson G. Case Page.2 October 21, 1974 bypass piping were obtained from this same heat.
Chemical tests to-date have indicated no property that would affect performance of the steel.
A review of the fabrication records indicates the piping was installed in accordance with design requirements.
In addition, when the piping repairs were made at Dresden Unit 2 and Quad-Cities Unit 2, no " Cold Spring" or excessive pipe movement was observed.
The cracks were associated with piping in which the valve is closed and there is no flow during routine power operations.
Interim Corrective Measures On the basis of these interim results, certain conclusions can be drawn relative to proper interim corrective measures.
To-date, the interim corrective measures are:
replacement of the sections of piping containing cracks, consideration of opening the valve in the bypass piping to reduce thermal stress and any postulated corrosion effects of non-flowing water.
Final Report Final reports from the various consultants to Commonwealth Edison Company are expected in November, 1974 The reports are expected to cover the following areas.
Metallurgical Examinations:
Miscroscopy Identification of corrosion products in the cracks Stress - Corrosion tests Chemical analysis of steel Stress Analyses:
ASME Code Finite element Dynamic Vibration Monitoring Results c
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Mr. Edson-G. Case Page 3 October 21, 1974 The schedule for reviewing these reports and developing the appropriate final conclusions and corrective actions is January, 1975.
It is planned to submit this information to you at that time; however, as significant new information becomes available, we will continue to keep you informed 'of the status.
Very truly yours, h g, J. S. Abel i
Nuclear Licensing Administrator I
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