Regional Basic Professional Training Course in Korea

Regional Basic Professional Training Course (BPTC) on Nuclear Safety
sometimes requires considering points a few hundred kilometers from the future plant. In
the general case, however, and without implying that the perimeter studied is necessarily
circular, a radius of about a hundred kilometers around the site may well suffice. The
distances are smaller, in the low tens of kilometers, for volcanic risks (lava flows and
mud slides and scattering of boulders and ashes).
The local scale corresponds to the area that can influence discharges and may be exposed
to geological risks such as landslides. It therefore concerns a radius of tens of kilometers
around the site. This is also the distance at which occurrences of surface fracturation are
generally surveyed. The local geological map is used as base for the hydrogeological
study of the site.
On the scale of the site, for which there is always a fine‐meshed investigation, the
problem concerns in particular the vertical depth of investigation.
5.3.1.4. The problem of liquefaction of soils
The question of possible liquefaction of the ground is important insofar as it is a
characteristic likely to lead the safety authorities to reject the site. In fact, this risk results
from a combination of an earthquake level high enough to cause loss of cohesion of the
subsoil under a periodic dynamic loading and a clearly defined size distribution of the
foundation rock below the water table. This is therefore a rather rare general case. When
the earthquake magnitude expected at the site is not negligible and the size distribution of
the soils under the planned plant is in the range of rocks subject to liquefaction, there
must be a thorough analysis of this contingency, by determining in particular the degree
of cohesion of the soils by in situ measurements and their liquefaction potential by
laboratory test.
For guidance, if the soils have a permeability greater than 10‐2 m/s they are analysed to
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