ML19329B231
| ML19329B231 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse, Oconee, Crystal River, Rancho Seco, Crane  |
| Issue date: | 11/18/1974 |
| From: | Mallay J BABCOCK & WILCOX, BABCOCK & WILCOX CO. |
| To: | |
| Shared Package | |
| ML19329B226 | List: |
| References | |
| NUDOCS 8001310583 | |
| Download: ML19329B231 (3) | |
Text
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b Babcock & WilCOX power ceneration creuo P.O. Box 1260, Lynchburg, Va. 24505 Telephone: (504) 384 5111 November 18, 1974 Dr. Donald F. Knuth, Director 4
Directorate of Regulatory Operations Office of Regulations U. S. Atomic Energy Commission Washington, D. C.
20545
Dear Dr. Knuth:
Attached please find ten copies of the report on the geaeric evalua-tion of the Significant Deficiency identified in the design of the attach-ment of the Control Rod Drive AC Breaker Cabinets to the floor for seismic excitation loadings. This deficiency has been reported to the affected utilities and remedial action has been initiated through field change packages. The attachment modifications described in the report are being factored into the design for later plants.
]
Plants affected by this deficiency are as follows:
%d Duke Power company Oconee Units 1, 2, & 3 Metropolitan Edison Company Three Mile Island Unit 1 Jersey Central Power & Light Three Mile Island Unit 2 Florida Power Corp.
Crystal River Unit 3 Sacramento Municipal Utilities Rancho Seco Unit 1 District Toledo Edison Company Davis-Besse Unit 1 Should you require additional information on the subject, please feel free to contact R. P. Williamson, the cognizant Licensing Engineer for Significant Deficiencies.
Very truly yours, BABCOCK & WILCOX COMPANY Nuclear Power Generation C 8
/
James F. Mallay JFM/fe Manager, Licensing Attach.
8001310 N The Babcock & Wilcox Company / Established 1867 m
3 Report on CRDCS Breaker Cabinet Seismic Oualification
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This report, pursuant to 10 CFR 50.53(e) on Significant Deficiencies, is to document the investigation of the significant deficiency in the seismic qual-ification on the Control Rod Drive Control System Trip Breaker Cabinets.
Identification of Problems A reevaluation of the seismic qualification of the control rod drive control system AC breaker cabinets has found that the recommended attachment of the cabinet to the floor is inadequate to withstand the SSE acceleration levels.
Analysis The Control Rod Drives are tripped by Loss of Power to the Drive Statore. Power is interrupted by disengaging either the AC or DC CRD breakers.
Should the breaker function be disabled in some manner, the Control Rods would have to be driven into the core to shut the reactor down.
In the event of an SSE, the AC Breaker Cabinets could, as per the finite element stress analysis, break loose from the floor mounting. With the cabinets unattached, the random motion or even falling over could cause accelerations of the bre-'eers that have not been analyzed or damage to the breakers, wiring, or connections which could compromise the ability of the breakers to trip the control rods.
Analyses cannot show that the failure will always be fail safe. Therefore, the deficiency in the design of the structural attachment of the AC Breakers Cabinets to the floor could adversely affect safety. This problem is thus considered to be a Significant Deficiency as per 10 CFR 50.55 (e).
Corrective Action The it:3chment of the AC Breaker Cabinet to the floor has been redesigned (see at'. ached figure ).
Depending upon the arrangement at the particular site, either additional bolts will be included or a series fillet welds will be added to increase the attachment strength. Each plant with a construction permit or operating license is being evaluated on an individual basis. Newer plants are employing cabinet holddown designs which will assure the ability to withstand SSE loadings.
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