Areva EPR

The dedicated corium spreading and cooling area is a core-catcher
equipped with a solid metal structure and covered with “sacrificial”
concrete. It aims to protect the nuclear island basemat from any
damage, its lower section features cooling channels in which water
circulates. The aim of its large spreading surface area (170 m 2 ) is to
promote the cooling of the corium.
The transfer of the corium from the reactor pit to the spreading area
would be initiated by a passive device: a steel “plug” melting under
the effect of the heat from the corium.
After spreading, the flooding of the corium would also be initiated by
a passive fusible plug-based device. It would then be cooled, still
passively, by gravity injection of water from the tank located inside the
containment and by evaporation.
The effectiveness of the cooling would then provide stabilization of the
corium in a few hours and its complete solidification in a few days.
Containment heat removal system
and long-term residual heat removal device
In the eventuality of a severe accident, to prevent the containment
from losing its long-term integrity, means would have to be provided
to control the pressure inside the containment and to stop it from
rising under the effect of residual heat. A dedicated dual-train spray
system with heat-exchangers and dedicated heat sink is provided
to fulfil this function. A long time period would be available for the
deployment of this system by the operators: at least 12 hours owing
to the large volume of the containment (80,000 m 3 ).
A second mode of operation of the containment heat removal system
enables to feed water directly into the core-catcher, instead of into
the spray system.
Collection of inter-containment leaks
In the eventuality of a core melt leading to vessel failure, the
containment remains the last of the three containment barriers; this
means that provisions must be taken to make sure that it remains
undamaged and leak-tight. For the EPR, the following measures have
been adopted:
•a 6 mm thick metal liner internally covers the pre-stressed concrete
inner shell,
• the internal containment penetrations are equipped with redundant
isolation valves and leak recovery devices to avoid any containment
bypass,
• the architecture of the peripheral buildings and the sealing systems
of the penetrations rule out any risk of direct leakage from the inner
containment to the environment,
• the space between the inner and outer shells of the containment is
passively kept at slight negative pressure to enable the leaks to
collect there,
• these provisions are supplemented by a containment ventilation
system and a filter system upstream of the stack.
Containment heat removal system
Spray nozzles
x
x
Passive
flooding
device
x
CHRS
(2x)
Corium
spreading area
In-containment refueling
water storage tank
Melt flooding via cooling device
and lateral gap
x
Water level in case of water
injection into spreading area
FL Flow limiter
I 51