Areva EPR

■ EPR NUCLEAR ISLAND
PRESSURIZER
†
The pressurizer (PZR) role is to maintain the pressure of the
primary circuit inside prescribed limits. It is a part of the primary
circuit, and is connected through a surge line to the hot leg of
one of the four loops of that circuit.
The pressurizer is a vessel containing primary water in its lower part,
and steam water in its upper part. To accommodate some primary
coolant volume variation, the pressurizer is equipped with electric
heaters at its bottom to vaporize more liquid water, and with a spray
system at its top to condense more steam. Compared to previous
designs, the volume of the EPR pressurizer has been significantly
increased in order to smooth the response to operational
transients. This improvement provides a gain in terms of equipment
life duration and a gain in terms of time available to counteract
potential abnormal situations in operation.
Relief and safety valves at the top of the pressurizer protect the
primary circuit against overpressure. Compared to previous designs,
the EPR features an additional set of motorized valves; in case of
postulated accident with a risk of core melting, these valves would
provide the operator with an additional efficient mean to rapidly
depressurize the primary circuit and avoid a high pressure core melt
situation.
A number of construction provisions have improved maintainability.
In particular, a floor between the pressurizer head and the valves
eases heater replacement and reduces radiological dose during
valve service.
All the pressurizer boundary parts, with the exception of the heater
penetrations, are made of forged ferritic steel with two layers of
cladding. The steel grade is the same as that for the reactor pressure
vessel. The heater penetrations are made of stainless steel and
welded with Inconel.
The pressurizer is supported by a set of brackets welded to the main
body. Lateral restraints would preclude rocking in the event of a
postulated earthquake or accident.
Pressurizer erection in a reactor building.
32 I