ML20128C270
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DEPARTMENT OF THE ARMY 50-424 M
OFFICE OF THE CHIEF OF ENGINEERS 50-425 WASHINGTON. D.C. 20314 426 neri.y To ATTDeTION ops DAEN-CWE-S 31 January 1974 bl Cs i
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Mr. T. Cardone FEB1 1974 > _
Site Analysis Branch
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7, Directorate of Licensing I.' ~.'/y/
Atomic Energy Comission
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Dear Mr. Cardone:
Inclosed are Geology Branch coments on Amendment 13 for the Alvin W.
Vogtle Nuclear Plant as requested by telephone conversation on 30 January 1974.
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t 1 Inc1 ERNEST L. DODSON As stated Chief, Soil Mechanics Branch Engineering Division-Directorate of Civil Works 8505280234 841015 g
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30 January 1974 ALVIN W. V0GTLE NUCLEAR PLANT SAVANNAH RIVER GEORGIA POWER COMPANY Of original concern to. this office was the relatively small number of borings which penetrated the clay-marl stratum which will comprise the foundation for the four reactor units at this site. Inasmuch as this formation is in part calcareous and contains many limestone lenses, the distinct possibility existed that undetected solution voids or channels could occur directly beneath these critical and heavy reactor structures.
The only rational method for investigating this possibility was to put down more borings and conduct more downhole geophysical and hydraulic pressure tests within the marl bearing stratum at the specific ' locations of these nuclear structures.
The Georgia Power Company has now performed a substantial amount of additional borings and downhole testing to firm up the essential engineer-ing properties of this bearing stratum.. Twelve additional core borings were drilled at the specific locations of reactor units 1, 2, 3 and 4 and penetrated completely through the marl stratum. Generally, good core recovery (90 to 99 percent) was experienced with these borings indicating minimal or no solutioning of the formation. Additional confirmation was
- secured by hydraulic pressure tests conducted in several of these borings with practically no water loss. One boring however, No. 516 in Reactor Unit 2, recovered only 44 percent of the core material penetrated. The reason for this core loss should be explained as related to causes other than solution voids, particularly since there was also no hydraulic pres-sure testing performed in this particular boring.
Except for not at the moment being able to explain the abnormally low core recovery on Boring No. 516, it is the opinion of this office that. the additional borings and testing program have satisfactorily proven the
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bearing capacity of' the clay-marl formation for all structures.
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- NO M N A. DIXON Staff Geologist, Geology Branch Engineering Division Directorate of Civil Works
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