ML20234D876

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Marked-up AEC Div of Licensing & Regulation Rept to ACRS on Bodega Bay Reactor
ML20234D876
Person / Time
Site: 05000000, Bodega Bay
Issue date: 02/03/1964
From:
US ATOMIC ENERGY COMMISSION (AEC)
To:
Shared Package
ML20234A767 List: ... further results
References
FOIA-85-665 NUDOCS 8709220221
Download: ML20234D876 (6)
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February 3, 19S I

!l ATOKIC ENERGY COtt4ISSION DIVISION OF LICEfiSI iG ASD REGULATION REPORT IV ADVISORY COME2 TEE ON REACTOR SAFEGUARDS ON BODECA EAY REACTOR I

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Rote by Director, Division of Licensing and Regulation The attached report has Oeen prepared by the r mbers of the Begulatory Staff for consideration by the Advisory Cernmittee on Reactor Safeguards at it.s February 19% :seeting.

8709220221 851217 PDR FOIA FIRESTOBS-665 PDR

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REPORT 'IU ADVISORY ColWITTER ON REACTOR SAFEGUARD 8 i

BOIEGA BAY REACTOR

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1. INTRODUCTION .

i The purpose of this report is to describe the issues 2*ised I by the recent reports from the Geological Survey and PG&E concerning l

the geological-seismolo6 1 cal aspects'of the Bodegn Bay reactor site, and to describe the differing interpretations of data derived from I

field observations at the site. The purpose of the reports prepared by the GeologLcal $ttrvey and PG&% is to provide a basis for estimating the probability of s rupture of the near-surface granitic rock at the reactor site and the maximum extent of such a rupture. (The maximum l

acceleration which might be expected at the reactor site due to l potential earthquakes is not to be discussed at this time.)

II. DICCU3SION i

There are two principal considerations that relate to the problem under consideration. The first is the cause of the offsets in the bedrock and overlying sediments which were discovered in the l Bodes Bay excavation, and an estimate of the time of occurrence of these offsets. The second consideration is the similarities differences octween Bodega Head and other areas (such as Point Reyes) vnich are approximately the same distance from the San Andreas fault ao Bodep Head and where surface ruptures vere observed in 1906 at i

the same or greater distance frcxn the main Sen Andreas fault line

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2 than is the proposed reactor site.

A. Offsets Discovered in Exc tion With respect to the offse s found in the bedrock in the exca-vation, there is apparently no/ disagreement that these offsets were tectonic in origin. With respect to the offset'in the overlying sedi-i ments, the authcra of the Geological Survey Report maintain that this l

offset is also tectonic in origin and is directly related to the fault in the bedrock. Their evidence for this is primarily the continuation of the fault from the bedrock into the ceciments at the southwest corner of the excavation, and the ability to trace the offset upward in the sedinents at the southwest side to the plus 25-foot level and horizontally across the 25-foot level for scue 150_ feet. On the other hand,PG&E(bntai that the offset in the sediments is not clearly tectonic in origin and, although genetically related to the fault in yt ,

the bedrock, might have been caused by landsliding or subsidence.

Their incipal rguments for this view are the inability to find the

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/ offset in the sediments above the plus 25-foot level and the fact that the i f

continuation of the offset outside the pit to the southwest at the minus 5

- t level is not directly in line with the offset in the sediments in the pit but is horizontally transposed by some 8 feet.

(The authors of the M-Geological Survey Report believe that this lack of alignment due to

'en echelon ' faulting. ) The second basis for PG&E's doubt as to the f tectonic origin of the offset in the sediment is the fact that there

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3-is no evidence of the offset extending from the bedrock to the sedi-ments in the northeast corner of the excavation.. (The authors of the f

Geological Survey Report believe that this is probably due to the fact' ~

that the sediments inanediately above the bedrock in this location are made up of an unconsolidated sandy clay which could absorb substantial movement by plastic deformation without t g, and point out that y -- A in the southwest c } of the excavation the offset, was also untrace-able in several feet of similar caterial.)

PG&E further igns that what.ever the cause of the offset in the sediments, the fact that it dms not extend to the surface indicates that the offset occurred more than hP,000 years ago, since carbon dating of the undisturbed upper layers of sediment has shown them to have an age greater than 42,000 years. The authors of the ih g[

Geological Survey Report maint i. that this is not positive proof of the minimum age of the offset in the sediment, since the absence of the offset in the upper sedimenta can be attributed to dying out of the faulting as it progresced upward.

B. Surface Ruptures West of the San Andreas Fault Zone The authors of the Geological 9urvey Report there in ooe significant similarity betveen Soder;a Head and Point Reyes .,y as the otherf, sever.-al location 6e_r_e rurface rupturing outside the W ...---~

cain 3en Andrea., ibult vss observed in 1906. That similarity is the I

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a close proximity of Bodega Head to the San Andreas fault. A geologic report written in 1908 describes and illustrates surface ruptures in

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the town of Inverness (on Point Reyes) that resulted from the 1906 earthquake. - This area was revisited m cently by the authors of the Geological Survey Report and the probable location of the rupture, about 2,000 feet vest of the projected edge of the San Andreas finuit

. 1 shown on the published geolo61 cal maps, was identified. The reported l

l horir.ontal displacement along th'scrack i was 2-1/2 feet. The authors  ;

of the Geological Survey Report believe that this rupture was undoubtedly due to tectonic fault movement.

P&cE's consultants confim the significance of the rupture in 1906 at Point Reyes .by =t t he ould not recommend reactor ,

1 construction in thlo area (apparent].y because they believe there is j 1 I a high probability of a futuro rupture in this location . - However, they c/~ Yaintainit here are significant differences between Bodega and ,

1 Point Reyes. In their view, the principal difference is the lack of -

surface indications of old fault lines n Bodega, in contrast to the l  % ( q.

l presence of such indications in Point Reyes, and the fact that most) N q - _p g _ - r_C~"Cw . -

[o_f the 1906 ruptures 4 at Point Reyes occurred ak these old fault D' ,\

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lines. The authors of the Geological Survey Report are not sure >

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) thnt these dissL911arities in fact exist since they have not closely /

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( 'j ex=ined Bodeca Et:nd frau.thic standpoint. They also point cut there vere .~.o coed observations code of pessible surface ruptures cade at Dodega in 190 5, as was done at Point Eeyes, and that it is possible that any 1906 rupture at BoleEn Head cculd now have been obliterated I

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due to the passage of time. In confirmation of this latter point, they state that same known 1906 ruptures along the main San Andreas ,

fault are not now detectable by surface inspections. f III. PGhE AND GEOLOGICAL SURVEY CONCIDSIONS PG&E maintains that because of the apparent age of. the offset in the sediments of the Bodega excavation, regardless of its cause, and because of the differences between BodeEn Head and Point Reyes,  ;

l the probability of a rupture in the near-surface granitic rock at j Bodega Head greater than one inch is so small that it can be dis- t counted.

The authors of the Geological Survey Report aintain)that because of the proximity of Bodega Head to the San An'dYr fault, l irrespective of the cause and the age of the offset discovered in the site excavation and irrespective of other differences or simi-laritier between Bodega Head and Point Reyes, a rupture of the near-surface granitic bedrock at Bodega Head of several feet but may occur, Nd be taken into consideration in detennining the suitability of the proposed site for the reactor.  !

The ultimate question to be decided is whether PG&E has made;-

1 7 a convincing showing thnt an ' exception" should be made fra:t the (s J \

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guides in Part 100 vith respect to the minimum distance of a reactor ./ '  ?

from a major fault without a s16nificant increase in the probability of a catastrophic accident.

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