ML19319E110
| ML19319E110 | |
| Person / Time | |
|---|---|
| Site: | Rancho Seco |
| Issue date: | 08/21/1974 |
| From: | Mattimoe J SACRAMENTO MUNICIPAL UTILITY DISTRICT |
| To: | |
| References | |
| NUDOCS 8003310618 | |
| Download: ML19319E110 (2) | |
Text
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SACRAMENTO MUNICIPAL UTILITY DISTRICT C 6201 S Street, Box 15830, Sacramento, California 95813: [916) 452-3211 August 21, 1974 Dr. Donald F. Knuth, Director Directorate of Regulatory Operations U. S. Atomic Energy Commission Washington, D. C.
20545 Rancho Seco Nuclear Generating Station No. 1 CRDC's AC Breaker Cabinet AEC Docket No. 50-312
Dear Dr. Knuth:
During review of the control rod drive controls cabinet seismic qualification at Rancho Seco Unit No. 1, it was determined the existing analyses and tests did not adequately demonstrate qualification of the f)s, equipment to the required acceleration levels. Babcock & Wilcox sub-(
sequently performed a re-analysis and further equipment qualification tests.
During this re-analysis, it was determined that the floor attach-ment of the AC breaker cabinets was inadequate to withstand peak accele-ration levels.
In accordance with the District's quality assurance procedures, this condition was determined to be a reportable "signifi-cant deficiency" as defined by 10CFR50.55(e).
Description of Deficiency - The control rod drives are tripped by loss of power to the drive stators. Power is interrupted by dis-engaging 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 analysis, break loose from the floor mounting. With the cabinets unattached, the random motion of this equipment or even falling over could cause accelerations of the breakers 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 con-sidered to be a significant deficiency per 10CFR50.55(e).
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Dr. Donald F. Knuth August 21, 1974 i
Corrective Action - The attachment of the AC breaker cabinet to the floor has been redesigned and fillet welds added between the cabinet and the floor mounting to assure a stable installation. The attachment of the cabinet to the floor will eliminate the random motion that has not been analyzed. The required field modification will be completed by September 1, 1974.
Should additional information on this prc'21cm be needed, or if we can be of further aseistance, do not hesitate to call.
i Sincerely yours,
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J. J. Mattimoe Assistant General Manager and Chief Engineer cc:
R. H. Engelken Region V 4
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