ML19319D860
| ML19319D860 | |
| Person / Time | |
|---|---|
| Site: | Rancho Seco |
| Issue date: | 07/11/1974 |
| From: | Mattimoe J SACRAMENTO MUNICIPAL UTILITY DISTRICT |
| To: | |
| References | |
| NUDOCS 8003260946 | |
| Download: ML19319D860 (2) | |
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SACRAMENTO MUNICIPAL UTIUTY DISTRICT C 6201 S Street. Box 15830, Sacramento. California 95813; (916) 452 3211 July 11, 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 Spray Pond Piping Seismic Modification
Dear Dr. Knuth:
We were recently informed by our architect-engineer, Bechtel Corporation, that the spray pond piping system will not pass the worst case seismic loads should such an event occur.
In accordance with our quality assurance procedures, this condition has been reviewed and has been determined to be a reportable "significant deficiency" as defined by 10CFR50.55(e).
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Description of Deficiency - The Rancho Seco Unit No. 1 spray ponds are designed and built in accordance with plant design basis earthquake criteria. They must be operable following a postulated earthquake. The spray pond distribution system consists of an all stainless steel piping system. The main supply header is a 24" line which runs about two feet above the pond bottom across the center of the pond and is supported by saddles resting on the pond basin. There are four 20" risers which supply water to the four lengthwise spray headers of decending size piping. The four lengthwise headers are supported on a column about ten feet high above the pond floor.
In checking the spray pond piping system seismic calculations, it became apparent that the loads resulting from a postulated earth-quake combined with pond operation exceed the allowable design stress.
Application of the code stress intensification factors resulted in an over-stressed condition in the four 20" risers to the 24" main header weld joints and also in the 20" risers to 14" welds on the horizontal distribution piping.
Corrective Action - Several alternative solutions were considered on how to reduce the seismic loading on these weld joints.
Rancho Seco Unit No. 1 has selected the addition of four 20" expansion joints on each pond as the best solution to this problem.
These eight new 20" stainless steel bellows type expansion
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joints have been purchased and will be installed prior to criticality
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i Dr. Donald F. Knuth July 11 1974 i
of the plant. These expansion joints are located above the water level and de-couple the seismic loading forces of the lower header from those of the four upper horizontal distribution system headers. By using these expansion-joints, the resulting stresses are conservative and well within allowable design limits.
Should additional information on this problem be needed, or if we can be of further assistance, do not hestitate to call.
Sincerely yours, h.b mt&~W
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'. Mattimoe Assistant General Manager
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and Chief Engineer cc:
R. K. Engelken (AEC, Region V)
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