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50-323 Mr. William P. Gammill, Chief 2 1974 > $
Site Analysis Branch Cumy Directorate of Licensing D
Wit SET, m.ar Office of Regulation Mk' b N.. # '
U. S. Atonic Energy Commission Washington, D. C.
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Dear Mr. Gammill:
Enclosed for your information is a preliminary review of aspects of geologic data presented in the FSAR for the Diablo Canyon Nuclear power plant site, unita 1 and 2, California (AEC Docket Nos. 50-275 and 50-323).
As you know, Mr. H. C. Wagner of our Office of Marine Geology is preparing a review of offshore geophysical data collected by the Geological Survey and by the applicant. We expect this review to be completed shortly.
Sincerely yours, L
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Elmer H. Baltz Deputy Chief for Engineering Geology Office of Environmental Geology Enclosure i
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Preliminary Review Diablo Canyon, Calif.
F. A. McKeown January 23, 1974 Pacific Gas and Electric Company Diablo Canyon site, Units 1 and 2 San Luis Obispo County, California AEC Docket Nos. 50-275 and 50-323 Geology A preliminary review of the geological and seismological data presented in the Final Safety Analysis Report (FSAR) for the Diablo Canyon nuclear power plant site, Units 1 and 2, indicates the need for additional information.
The report appears to have included
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. data and discussions of nearly all geologic and seismologic features pertinent to the safe operation of the plant. One feature, however, for which adequate information is not provided is an offshore fault or structural zone which has been. recognized since presentation and review of the Preliminary Safety Analysis Report (PSAR).
The principal geologic and seismologic features of importance to the site are small faults near or within the site area and large faults along which large earthquakes may occur several miles from the site. The occurrence of small faults that do not cut terrace deposits near and within. parts of the plant site is documented and explained in sufficient detail to accept them as noncapable faults within the definition of AEC criteria for capable faults. The proposed four maximum earthquakes (pages 2.5-12 and -13) that could i
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However, since these four possible
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earthquakes were proposed by Benioff and Smith (1967), a fault or structurally disturbed zone with a length of 90 miles or more that a
passes within 7 or 8 miles offshore of the site has been interpreted by Hoskins and Griffiths (1971).
This structural zone is discussed on pages 2.5-10, -11, and
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-67 of the FSAR. As stated by the applicant on page 2.5-67 "Available data for the reported offshore structural zone are not conclusive for determining its extent, continuity, and state of activity." The applicant's descriptions of the zone are taken from the work of Hoskins and Griffiths who show it as a fault. Their interpretations of the displacements along the zone, which the applicant presumably accepts, do not indicate that the sea floor or Holocene deposits have been offset. The basic data upon which the interpcetations have been made, however, are not presented by either the applicant or Hoskins and Griffiths.
Seismic activity along and in the vicinity of the zone is shown in figures 2.5-3 and 2.5-3A and discussed on page 2.5-67 in the FSAR.
It is probable that the accuracy of the i
locations of the earthquake epicenters shown in the figures is too poor to relate them conclusively to the zone; conversely, they 1
1 cannot be disassociated from the zone.
The question of whether the zone is a fault or contains faults that are capable within the l
definition of AEC criteria is therefore unresolved.
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Because of the apparent length and proximity of the offshore zone to the site, consideration of the zone as another possible source of a maximum earthquake in addition to the four propcsed by the applicant may be necessary. Until definitive information is presented to demonstrate otherwise, prudence requires that the zone be' considered capable.
References
- Benioff, H., and Smith, S. W., 1967, Seismic evaluation of the Diablo Canyon site, Diablo Canyon, Unit 1: PSAR Docket No.
50-275, and Diablo Canyon Unit 2: PSAR Docket No. 50-323.
Hoskins, E.
G., and Griffiths, J.
R., 1971, Hydrocarbon potential of northern and central California offshore, irt Cram, I.
H.,
ed., Future petroleum provinces of the United States--their geology and potential:
Am. Assoc. Petroleum Geologists Mem.
15, v. 1, p. 212-218.
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