Earthquakes - Geotechnical Engineering Investigation - page 972

operation. Some portions of the plant needed for power generation but not
required for safe shutdown or radiation protection, however, need not be
designed to resist the OBE and conceivably the plant could cease to produce
power if subjected to an event of OBE magnitude. Category 1 structures are
those critical to safe operation and shutdown and include the reactor contain-
ment; the auxiliary, fuel handling, radioactive waste, and control buildings; and
the intake screen house at the cooling water source. The OBE is often substan-
tially lower than the SSE.

Safe-shutdown earthquake ( SSE ) is the largest vibratory motion that could con-
ceivably occur at any time in the future. The operator must be able to shut the
plant down safely after such an event, even if some of the plant components are
damaged.

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Approaches to Selection
Standard Approach
Conventional structures in areas of low seismic hazard are based on selection of values for
g , and normally such values are obtained from existing publications such as national or
local building codes, or seismic risk and probability maps such as Figure 11.14.
Alternatively, if there are no published criteria, as may be the situation in many countries,
g may be estimated from records of intensity or magnitude by conversion, using relation-
ships such as Figure 11.13, Table 11.14, or Equation 11.10. In unfamiliar areas without build-
ing codes, if the hazard degree is in doubt, then a site response study is undertaken.

Comprehensive Approach
Design of unconventional structures or structures in high hazard zones ( Section 11.4.5) is
based on the selection of values for peak effective horizontal and vertical g , frequency con-
tent, and duration.
Existing data are collected and reviewed within a radius of about 200 mi (320 km) (NRC,
1997) from the proposed structure, including catalogs of intensity reports and event mag-
nitudes, strong-motion records, geologic maps, known faults, and other information, and
a site response study is performed.

TABLE 11.14
Design Seismic Horizontal Ground Motions a

Design Acceleration (gravities g ) Design Velocity (in./sec)

Magnitude b Ground Motion c Structures d Ground Motion c Structures d

8.0 0.60 0.33 29 16

7.5 0.45 0.22 22 11

7.0 0.30 0.15 14 7

5.5 0.12 0.10 6 5

a

From Hall, W.J. and Newmark, N.M., Proceedings of ASCE , New York, 1977, pp. 18-34. With permission.

b

Magnitudes are considered as the design maximum earthquake (were developed for four seismic zones along
the trans-Alaska pipeline).

c

Ground motion: Peak values which may affect slope stability, liquefaction of cohesionless materials, or apply
strains to underground piping.

d

Structural design: Peak values used for design of structures or other facilities Since they account for structural
features and response, and soil-structure interaction, they are generally less than those used to define soil
response.