ML20235C716

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Clarifies Question 4 of AEC Re Util Procedure & Criteria Used in Design of Structures & Components to Withstand Oscillations & Vibrations from Major Earthquake
ML20235C716
Person / Time
Site: 05000000, Bodega Bay
Issue date: 06/02/1964
From: Price H
US ATOMIC ENERGY COMMISSION (AEC)
To: Whelchel C
PACIFIC GAS & ELECTRIC CO.
Shared Package
ML20234A767 List: ... further results
References
FOIA-85-665 NUDOCS 8709240549
Download: ML20235C716 (7)
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l' Mr. C. C. '.ihelchel l Vice-President Pacific Cas and Electric Company 245 Market street San Francisco, California

Dear Mr. Whelchel:

Question 64 of our letter of May 19, 1964, referred to the need for clarification of the procedures and critaria Pacific Cas and Electric Company proposes to use in the design of the structures and components t.o withstand oscil-lations and vibrations from major earthquakes. After further study and discussions with our consultants and advisers it appears that some amplification of this question and its relation to question fl of our previous letter is in order.

The opinion is held by some that the spectrum of ground motions in case of another r.sajor earthquake on the San Andreas fault may be more severe than that which occurred in the El Centro earthquake. Further, such an earthquake might be accompanied by shear displacement. up to a possible 3 feet, and would likely be followed by aftershocks which might be as large as the El centro earthquake of 1940.

Against the possibility of earthquakes of these dissensions, we would like to explore the design arrangements and their feasibility in protecting the plant against damage which would result in hazards to the health and safety of the public. We request Pacific Cas and Electric Company to consider these questions:

1. Assume an earthquake having a vibration spectrum similar to that of El Centro but with maximum acceleration of 2/3 g* velocities up to 2k f t./sec. ; ground displacements
  • The marimum of acceleration , velocity and displacement would not occur for the same periods of vibrations.

8709240549 051217 PDR FOIA FIRESTOBS-665 PDR I

4 C. C. Whelchel up to 3 ft.; shear displacement (faulting) of 2 ft, in the foundations of the plant, and with the occurrence of an after-shock equal to El Centro before remedial action could be taken.

Mtat plant arrangements , design criteria and procedures could be developed to prevent i
apairment of functions of struc tures ,

equipcent and systems important. to safety? This should include an analysis indicating the margins to allowable stress or deformation limits.

2. Assume an earthquake having a vibration spectru:n siailar to that of El Centro but with accelerations generally s up to 2/3 g plus intermittent pulses of acceleration up to 1 g*;

velocities up to 2 ft./sec.; ground displacements up to 3 ft.;

shear displacement (faulting) in the plant foundations of 3 f t. , and with the occurrence of an af tershock equal to El Centro before remedial action could be taken. What plant arrangements, design criteria and procedures could be developed which would assure shutdown and maintenance of the plant in safe shutdown conditioni Sincerely yours.

Harold L. Price Director of Regulation

  • See footnote on page 1 REG.

HLPrice:vl 6/2/64

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  • Williamson - 5/15/64 Revised - 6/1/64 QUESTIONS RESULTING FROM ACRS MEETING OF MAY 8 '

' Differential Displacement under Reactor

' Displacement isolation of a structure of this nature, to the writer's '

. knowledge, has no precedent. Consequently, all vital problem areas involved must be thoroughly explored and solutions provided as a pre-requisite to acceptance. .

.'Accordingly, it is importa.nt'that the applicant develop a complete pre- .

timinary design of a displacement isolation syste'm to accomodate diff- '

erential displacements of rnagnitudes acceptable to the AEC. This effort should include ' complete back-up calculations and drawings, and ,

I test data where needed. The scheme should be submitted for review, and should be reviewed by one or more authorities in this field,'such as Dr. Newmark.

The displacement isolation schemes whi.ch have been considered utilize an annular space between the surface of the excavation and the exterior j

i wall of the structure. This space may be open or filled. These schemes j j

.~ involve certain general problem areas involving ' questions and considerations e' F l

- such as the following: '

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. J With regard to the open annulus, can a ring wall be designed to prevent

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encroachment on the clearance due to cave-ins before or during an earth- N N.

quake?

The filled annulus leads to questions relating to the filler material. # [

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3 l l (1) The material must be sufficiently compressible and of the necessary thickness to accommodate the required displacement without locking. On the other hand it must not be so rigid as to overstress the walls of the containment. Data should be provided regarding stress strain charac-teristics under the anticipated strain rates, including effect of pore water.

(2) The material in place must have properties which are predb..able and consistent. (3) The materiati must be durable and must undergo negligible change in properties with time or environmental conditions. A specific question arising here is the effect of ground water, both with regard to the factor of durability and compressibility. The material preferably should not yield significantly under earthquake vibrations in absence of differential displacement and should not compact under the weight of the material above. If there is this possibility, the thickness, or strength, should be increased, appropriately. (4) Buoyancy of the material must be properly considered if ground water is present.

Further questions arise, with regard to the integrity of the structure. If the isolation system contemplates contact of the structure with the rock wall of the excavation at the shear plane, it should be demonstrated that the wall can resist the resulting pressures with a reserve margin suffi-cient to permit some further displacement without violating the containment.

If the isolation ' scheme contemplates sliding of the structure to accommodate a part of the total displacement, it should be shown that this can occur without violating the containment. If a filled annulus is used, this calculation I

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3 should account for the fact that the load along the line contact at the shear plane may be greatly increased due to compression of the fill on the far side. It is likely that pressures at the contact will puncture l

the wall locally before movement of the structure can occur. l In addition to demonstrating integrity of the structure walls, it should

  • be shown that all internal load paths , including those provided by floors ,

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and radial walls are adequafe' to transmit the loads. Where appropriate, these components should be considered as rings and diaphragms trans-ferring loads by shear into the outside walls or other resisting elements. ~ -

If vertical displacements arte considered credibic, the annular space provided should be adequate to accommodate tilt of the structure in com-bination with horizontal displacement. The base of the structure and all other features should be shown to be adequate for the resulting stresses ,

when combined with stresses from the horizontal displacement. It is

, equally as important to be certain that tilt does not lead to internal mal-function of the reactor of a hazardous nature.

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If it is found necessary to enlarge the existing excavation, a reasonable approach that avoids uncertainties which otherwise could occur would be to provide sufficie~.c ent'argement to prevent contact between the structure and the displaced rock surface under the anticipated displacements... The, g

w gap separating structure and displaced rock surface should be sufficient l

to allow some additional di,splacement without causing structural damage.

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It should be noted that the cost of an annulus of concrete fill would be something less than $40,000 per foot of thickness, which is not a large price to pay for using this kind of an approach. The cost of additional excavation per foot of thickness is perhaps less certain, and might depend on the increase in diameter. However, it is doubtful that this cost would exceed the cost of the concrete fill.

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It is likely that, at the present time, the applicant has not sized the i i

structural components of the building in final form or determined the i reinforcing steel requirements. Hence, in theory, it is not possible at this time to evaluate the effect of stresses due to differential dis- f placem ent. In actual fact,' what is desired is not a precise stress '

analysis. What is needed is an estimate of feasibility to determine whether it is possible to resist all forces involved under the hypothetical i s

carthquake and associated displacement, plus all other concurrent loads, using member sizes, wall thicknesses, and steel percentages which are r

within the realm of reason. I

. Self Sufficiency of the Reactor Structure and its Internals

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Particularly where large displacements are considered, the question arises  ;

regarding the extent to which safety is dependent upon integrity of umbilical i features (vital components not supported by the reactor structure but con-nected to it.) These might include, for example, external water and power r

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5-N sources and associated piping. Verbal statements during the meeting '

of May 8 appeared to indicate that for a period of several hours or more the power and water sources within the reactor structure were sufficient without augmentation from outside sources. It seemed to be inferred

, that the station battery was ' sufficient to provide all power needs for at least a part of this period. This point needs clarification. ,-  %

W It is a known fact that auxiliary diesel generator units are not highly reliable. This prompts the question as to whether a backup unit is provided.

It also seems appropriate to ask for data regarding the type and frequency of maintenance and checkout procedures for such equipment.

If integrity of steam and feed water lines under the maximum differential displacement is considered essential from a safety viewpoint, then the feasibility of their survival should be supported by rough calculations.

These would serve to prove or disprove verbal statements previously made to the effect that this was not a problem. '

Tsunami Effects At the meeting of May 8 the problem of damage from tsunamis was argu ed to be negligible largely on the grounds that the yard elevation of + 25 gave protection on the harbor side, and the high bluffs gave protection on the ocean side.

Nothing was said regarding any special provisions for pro-s tecting the intake and discharge features from the effects of tsunamis, c

Further elaboration on protection of these features may be warrante'd, depending on how critical they are considered to be from a safety viewpoint.

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