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wasumarow.o. c.rous FEB 2 31984 i
LNOTETO: Nilesh Ch'okshi, Structural Engineering Section A Structural and Geotechnical Engineering Branch i
Division of Engineering FROM:
John T. Chen, Geotechnical Engineering Section Structural and Geotechnical Engineering Branch Division of Engineering I
SUBJECT:
COWlENTS ON LLL'S REVIEW 0F THE MILLSTONE NO, 3 i
PROBABILISTIC SAFETY STUDY
Reference:
'.Unreviewed Draft -- Review of the Millstone Unit 3 Probabilistic Safety Study Seismic Fragility, Wind, and External Flooding by John W. Reed, dated December 22, 1983 Following coments resulted from the review of the referenced draft:
1.
On page 1-4, the concern - the question of secondary nonsafety-related
-components failing and falling on safety-related equipment, has some merit and should be addressed in the PSS. Specifically in the geotechnical engineering area, the seismic-induced failure of circulating water pipelines which may affect the foundation support and-the safety function of the service water-pipelines and the electric duct. Also, the potential liquefaction of the shore front beach sand may-impair the safety function of the intake structure.
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2.
On page 2-17 the statement about the sliding coefficient of friction used for analyzing the sliding stability of the demineralization water storage' tank may not be true because the coefficient of friction between mass concrete and rock as used by the foundation engineer is only 0.7 when no test data is available rather than 1.0 as used. The thickness of base mat has no bearing on the coefficient of friction between two dissimilar materials.
3.
On page 2-21, there is no discussion about the validity of the assumption that the failure of the service water pipeline is the same as the sliding fragility of the emergency generator enclosure. The supporting media, foundation conditions, for these two are significantly different from each other; therefore, the sliding fragilities are expected to be different.
I The discussion about the failure mode other than sliding of'the service water piping is of merit and should be investigated.
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' ' FEB 2 31984 Nilesh Chokshi On page 2-23, the' calculated design capacity 4.
If indeed the enbedment because the building is enbedded in 15' fill.
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has not been accounted for in the original calculation
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internal friction angle of 40' for the till as the friction angle conservative.
The between the till and the concrete footings is not appropriate.
emergency generator enclosure has a very com supported on both till and fill.,The friction factors used in the calculation should represent the as-built conditions.
On page 2-26, it was pointed out that the uncertainty values used It should, however, be pointed 5.
Millstone PRA were on the low side.out that the uncertainties Because the nature of soils than those assumed in the analyses.
which possess a wide range of engineering properties, i.e. strength shear modulus, damping ratios, friction angles.
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John T. Chea, Geotechnical Engineer Geotechnical Engineering Section f
L Structural and Geotechnical Engineering Branch Division of Engineering 4
cc:
G. Lear L. Heller y
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