Technology and Operation - Kernkraftwerk Gösgen

Safety precautions
Special emergency building.
The highest priority in reactor safety technology
is the safe enclosure of all the radioactive
fission products that are generated
during nuclear fission. The safety measures
must be designed to ensure that, during both
normal operation and incidents, no radioactivity
is released from the plant in an uncontrolled
manner which could present a danger
to people or the environment.
Preventing the occurrence of incidents is similarly
a priority. Administrative and structural
measures must be in place to detect malfunctions
at an early stage and to eliminate
these, or at least restrict their impact and ensure
that they do not escalate into an incident
which could affect the environment. Effective
safety precautions allow for the possibility
of faults and dysfunctions in both people
and materials. Systematic precautions
thus require a fault-tolerant technical plant
design with sufficiently large contingency reserves
to cope with any incidents too.
Inherent safety
In a light water reactor like the KKG, light water,
i.e. normal, purified and demineralised
water, is used as the moderator and coolant.
The coolant water moderates the neutrons
generated by nuclear fission; it decelerates
high energy neutrons emitted from the fuel to
the «thermal velocity» at which they can trigger
nuclear fission again.
The so-called inherent safety is based on the
properties of the moderator and the fuel. If
the coolant temperature increases and steam
bubbles form, then the density of the water is
reduced and fewer neutrons are decelerated.
At the same time, when the fuel temperature
rises, more neutrons are absorbed by the
fuel-carrier material, uranium-238, and hence
fewer neutrons are available to trigger nuclear
fission once again. Assuming a loss-ofcoolant
incident caused by a major leak, the
chain reaction would immediately come to a
standstill, both through the increased neu-
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