The Reactor Vessel is of cylindrical shape with hemispherical heads.

The construction material is low-alloy carbon steel, internally lined with austenitic stainless steel.

The main openings of the Reactor Vessel are the water/steam nozzles and the two connections to the Pressurizer.

Core

The reactor core consists of 69 typical (17 X 17) PWR fuel assemblies with a reduced length to limit pressure losses.

Steam Generator Unit (SGU)

The SG features an annular tube bundle with helicoidal tubing.

The steam is generated tube-side. The feed water piping is connected to feed water headers, located symmetrically inside the reactor vessel within a calm zone, provided each with two tubeplates laid out vertically. The tubes depart circumferentially from the tubeplates.

A similar arrangement is provided at the top for the two steam headers connections.

The vertical arrangement of the tubeplates aims at preventing crud deposition at the tube-to-tubeplate connections, where the corrosion is likely to occur.

The higher outer rather than inner tube pressure, a reversed situation with respect to a conventional SGU, reduces the risk of flaw growth in the tubes.

Primary Circulation Pumps

The two Primary Pumps of the variable speed, glandless, wet winding type (like the pumps manufactured by Hayward Tyler Fluid Dynamics) are fully enclosed within the Reactor Vessel. The pump motor is cooled by the water of the Intermediate Plenum.

Above Core Structure (ACS)

The ACS, shaped like a flat-bottom cylindrical glass, provides the support for the core instrumentation and forms the inner wall of the annular riser of the primary water. The ACS is open at the top. The water within it is part of the intermediate plenum and this helps to limit the primary water inventory in the reactor module to a minimum. The ACS is flanged to and suspended from the top of the Inner Vessel for easy removal to allow standard fuel handling.

Pressurizer

The Pressurizer is of a slim cylindrical shape with hemispherical heads.

The pressure control function is carried out in the upper part, which is externally insulated to limit heat losses from the steam and hot water plena.

The remaining bottom part contains a cold water plenum, hydraulically connected to the upper hot water plenum by means of a number of pipes.

The function of the pipes is to enhance mixing of the hot water with the cold water, in case of water flow towards the reactor vessel during transients.