Technology and Operation - Kernkraftwerk Gösgen

Safety precautions
extreme external impact involving the failure
of the switchgear building, the turbine building,
the reactor auxiliary building, the water
supply and the third-party supply. The feedwater
system, the start-up and shutdown system,
the emergency feed system and the special
emergency system have a total of eleven
pumps at their disposal for supplying the
steam generators. A single pump is sufficient
to ensure the removal of the residual heat.
The special emergency building is split into
two separate sections. Each of these sections
houses a train of the special emergency system.
The building is designed in such a way
that the special emergency system is protected
against external impacts, including aircraft
crashes, sabotage, fires and earthquakes.
Each train of the special emergency
system comprises a feedwater system, a
residual heat removal system, an additional
boron-injection system and well pumps, an
emergency power system, 48V batteries,
rectifiers, a reactor protection system, a demineralised
water tank with a capacity of 500
cubic metres, and an emergency diesel generator.
From each emergency feed pump,
there is a feed line to a steam generator. To remove
the residual decay heat, demineralised
water is fed into at least one steam generator.
The water evaporates, and the steam is released
into the atmosphere through the main
steam safety valves. The residual decay heat
can be removed over a period of ten hours,
without need for intervention by the operating
staff. The structural enclosure and physical
separation of the redundant sub-systems provide
protection against extensive impacts,
such as fire, flooding or even an aircraft crash.
The electrical cabling and cooling water pipes
are laid in separate locations, for example,
and the instrumentation and control system
lines are positioned in different sections of the
switchgear building.
In some cases, application of the fail-safe
concept provides additional protection. Wherever
possible, the safety systems are designed
in such a way that malfunctions or the
loss of the power supply will trigger appropriate
safety-related actions. The fail-safe concept
has been implemented, inter alia, in the
reactor emergency shutdown system, which
remains effective even if power is lost. The
control rods are attached to the drive mechanism
by means of electromagnets. If the
power is cut off, this retaining function is lost
and the force of gravity causes the rods to fall
into the reactor core and shut it down.
As result of the analysis of accidents abroad
(Three Mile Island 2 and Chernobyl), special
emergency measures (safety level 4) were
introduced which ensure that, even for very
rare accident scenarios (simultaneous multiple
failure of components and equipment),
the consequences for the neighbourhood of
the power plant will remain limited. To protect
the containment in the highly unlikely event
of a beyond-design-basis incident, a filtered
containment venting system was installed in
1993. Through controlled and filtered venting,
this system prevents containment failure due
to excess pressure. The system is activated by
opening the isolation valves and assures an
effective retainment of aerosols and iodine in
the scrubbing fluid. The separation efficiency
for coarse and fine aerosols is in excess of
99.9 % and for elemental iodine, in excess of
99.5 % percent.
Reactor protection system
The reactor protection system (safety level 3)
monitors the state of the reactor by measur-
� � � � �26 � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �