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Dr. David Okrent, Chairaca Advisory Cannittee en asacter Sefaguards U.S. Atomic tiergy Commission Dear Dr. Okrents Attached hereto, for the informattom of the ACES, is a preliminary j,
draft of criteria for locattom and design of reactor facilities in seismic areas which the regulatory staff is now trying to develop.
We would like to besia holding discussions of these criteria, as appropriate, with your subasamittee on saismic prsblans.
In the asentime, it is our intention to assemble in the immediate future.
i an ad hoc Industry Advisory Committee of technical entports in seienr fugy,.
geology and strusteral engineering from government organizations.
industry, and the universities, to assist as la developing these-cricevia
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into a more definitive fees.
There is, as you know. as ungent need for guide linae in this field.
We anticipate that greatest everall progress can be secemplished by securing the e-ht=1 contributions of emperts in the field as an effort osmechat is para 11e1 with ear dissensions with the Acts.
In this connection, it appeared to 'us that ceasemmic.ation 'ta this endeavor comld perhaps be facilitated if the Acts should delmate one of; their members and their tenhaisol esport semanitant, Mr. 8teinbrigge, to',)ein j
with the regetatory staff in its diosassions with the ladustry Advisory Comunittee of technical asperta.
We would like to discuss these possibilittee with the Acas.
Sincerely yours.
GM by C. K. Ben Clifford K.. Beck Deputy Director of Regulation Ate-h t:
Draf t of Seismic Criteria j
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11 KAPT II '.
C.K.itecL:vI I t '9 /06 CRITERIA RELATING TO SEISMIC FACTORS IN DESIGN J AND LOCATION OF REACTORS
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1.
A reactor should not be located within an active earthquake fault zone, nor at distances less than about 1/4 mile of the accepted boundaries of such a. fault zone. In some situations, depending on geology, the nature of the fault system, a distance greater than 1/4 mile may be required.
r It is not possible, with present knowledge to determine fully in all l
situations when a fault is active and when it is inactive; i.e.,
when further movements along the fault are likely and when they are unlikely to T
recur. However, for purposes of reactor location, some guidance can be given:
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a.
A fault system may be considered. inactive when it can be established that no movement has occurred in the fault system i
for 10,000 years or more.
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b.
Subsidiary, secondary, or sympathetic faults in areas tributary I
to active fault zones may be. considered inactive if it can be l
established that no movements along the aubsidiary faults have occurred for at least 10,000 years, even though faulting along l
the main fault system might have occurred more recently.
i c.
Where no evidence on dates of latest fault movements are l
available (e.g., no overburden) other evidence will be consic'ered l j
as available, i
l d.
In an area where seismic activity has occurred in recent times, but faulting is not evident or age of faulting is obscure, other evidence as available will be considered by experts in l
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l evaluating activity status-l 1
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2-2.
All reactors to be located in seismically active areas, in locations l
not otherwise excluded by these criteria, must be designed to withstand the
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I following conditions: (a) without impairment of function, the vibrational
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and ground displacement effects from an earthquake of the largest probable intensity (design earthquake) anticipated in the area within the lifetime of the structure; and (b) with the capability of safe shutdown, in the event 1
l of an unexpected " maximum credible earthquake" (MCE) in the area. Usually, I
l and in the absence of data to indicate otherwise, the nunerical values l
assigned to the MCE ground motions are double the values assigned to the i
ground motions of the design earthquake.
i 3.
All reactors should be designed in such a way that a permanent ground displacement of a few inches under the reactor or under the facility should l
l not cause disruption of the structures or functional impainnent of the systems.
l Where larger permanent ground displacements are credible, it may be feasible l
l to provide special design accommodations for these within limited ranges.
1 Otherwise, a different location will be required. The specific range of dis-l l
placements expected at a site must be established on the basis of the best information and expert advice available, and design accommodation for the appropriate range must be provided.
Such ranges are: (a) up to a few inches (for all reactors); (b) up to 2 feet; and (c) up to 5 feet. Where ground dis-placements of more than 5 feet are considered to be credible, the site should not be considered appropriate.
l 4.
The basic principles which should be considered in design to l
accommodate permanent ground displacement include the following:
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Provision of a fi rm base or raf t which enn support the faility
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without damage caused by the permanent g round displacement.
1 b.
Provision for absorption of energy or of relative motion by the use of a frangible or sof t isolation material around the sides of th '
a supporting structure.
Selection of material under the foundation which would permit l
c.
differential motfons of earth sections supporting the foundation..
j d.
Provision of flexible connections between elements'that are supported separately, to provide for relative motions in all I
possible directions.
Others ??.
e.
5.
In seismic areas, ground motions accompanied by transient ground vibrations present problems that can be overcome by appropriate design of reactor structures. By use of historical records and expert opinion the vibra-tional motions to be accommodated by design for (a) the design-basis earthquake and (b) the maximum credible earthquake, should be established, including:
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a.
Frequency range of vibrations b.
Transient ground displacements in vibratory motion c.
Maximum velocity d.
Maximum ground acceleration 6.
In design modifications to accommodate earthquake transient vibrational motions, the following basic principles should be taken into account:
Application of dynamic analysis procedures a.
b.
Development of energy absorption capabilities c.
Shock isolation d.
Strength of structural elements 1
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Flexibility or displacement of mechanisms or other elements c for strength is.not a design consideration, or in addition to strength as a design consideration.
f.
Dqmping factors g.- Stress level in structures.
'7.
Design consideration should be given to other ' factors affecting site suitability, such as:
l a.
Possibility of land slides-which would constitute a threat 1
to the facility.
b.
Possibility'of liquefaction or differential compaction of'the
'I supporting soil under the - facility.
c.
General subsidence that may cause large distortions of the facility.-j i
'l d.
Possibility of unrelieved stresses in bedrock underneath the plant.
t e.
Presence of solution phenomena or irregular weathering profiles 1
in underlying support layers beneath the plant foundations.
Where the magnitude of such factors at a given site may exceed the jl feasibility of design protection, a different site 'should be chosen. -
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8.
General: In structural design to accommodate earthquakes, consideration.
of the following aspects should be included:
j a.
The possible combination of motions in various directions, including vertically and horizontally, either simultaneously or J
l out of phase.
i b.
Relative transient and permanent displacement ~ motions between l
l different parts of the entire facility.
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Permanent displacement or fault motion'near the facility.
c.
1 d.
The forces caused by earth embankments. acting on-the structure or by impact between the structure and supporting elenents:
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or between individual parts of the components.in the facility.
e.
Combinations of accident either preceding an earthquake or triggered by.the earthquake,. combined with the transient and l
permanent motions in the earthquake.
I f.
The maximum wave action or flooding ef fect from-tsunamis either.
caused by or triggered.by. earthquakes.
In' exposed west coast
. locations protection against tsunami to heights of 28 or so feet; may be required.
g.
The relative degree of damping in' the different parts of the facility corresponding to the range of action or stress level' i
anticipated, i
h.
For all of the above, the values of the parameters defining the various motions or environmental conditions should be ' established
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in order that the structural design can. be accomplished. Where these amplitudes cannot be established accurately, at 1 cast their range or an upper limit must be estimated and justified.
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