Areva EPR

■ EPR NUCLEAR ISLAND
REACTOR PRESSURE VESSEL
AND INTERNAL STRUCTURES
†
The RPV has been designed to facilitate the non-destructive testing
during in-service inspections. In particular, its internal surface is
accessible to allow 100% visual and/or ultrasonic inspection of the
welded joints from the inside.
The RPV closure head is a partly spherical piece with penetrations
for the control rod drive mechanisms and the in-core instrumentation.
The RPV and its closure head are made of forged ferritic steel –
16 MND 5 – a material that combines adequate tensile strength,
toughness and weldability. The entire internal surface of the RPV
and its closure head are covered with a stainless steel cladding for
corrosion resistance. To contribute to the reduction of the corrosion
products radiation source term, the cladding material is specified
with a low Cobalt residual content.
Inside the reactor building, the entire RPV structure (including the
reactor core) is supported by a set of integrated pads underneath the
eight primary nozzles. These pads rest on a support ring which is
the top part of the reactor pit.
Chalon manufacturing plant (France): Civaux 1 (N4, 1,500 MWe) reactor pressure vessel
and its closure head.
Significant safety margin against the risk of brittle fracture (due to
material aging under irradiation) during the RPV’s 60 year design
life is ensured.
Reactor Pressure Vessel
The Reactor Pressure Vessel (RPV) is the component of the
Nuclear Steam Supply System that contains the core.
A closure head is fastened to the top of the RPV by means of a
stud-nut-washer set.
To minimize the number of large welds, and consequently reduce
their manufacturing cost and time for in-service inspection, the upper
part of the RPV is machined from one single forging and the flange
is integral to the nozzle shell course. Nozzles of the set-on type
facilitate the welding of the primary piping to the RPV and the welds
in-service inspection as well.
The lower part of the RPV consists of a cylindrical part at the core
level, a transition ring and a spherical bottom piece. As the in-core
instrumentation is introduced through the closure head at the top
of the RPV, there is no penetration through the bottom piece.
Reactor pressure vessel monobloc upper shell for the Olkiluoto 3 (Finland) EPR.
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