The large annular space between the core barrel shell and the reactor vessel contains the heat exchanger-pump modules. Each of the sixteen modules of Figure XIX-2 comprises a primary pump and a heat exchanger used to remove residual heat.

As shown in the figure, the submerged pump, is supplied with water exiting the steam generator. The coil-type motor is submerged downstream of the impeller. The pump motor has a stationary cylindrical stator surrounding the rotor that is connected to the pump’s impellers. Electrical power is supplied to each of the 16 pumps by cables through small penetrations in the reactor vessel. The primary water that flows around the outer ring cools the coils; therefore associated piping penetrations through the reactor vessel for cooling water are eliminated. The spool pump needs an additional external motor to provide high inertia during coastdown in order to mitigate the consequences of Loss — Of-Flow Accidents (LOFAs). This additional inertia, provided by an external motor with an adequate flywheel, is linked to the spool type pump by an electrical connection. At the outlet of the pump, water is accelerated by a venturi, passes into a diffuser and then through the decay heat exchanger tube bundles.

The decay heat exchanger of the RRP system (see XIX-4.1.2) consists of bayonet tubes whose outside surface is wetted by the primary fluid. The secondary water flows first in the internal tube and then upwards through the annular space bound by the two tubes. The water box is located in a dead zone, behind the venturi. This type of heat exchanger is of interest, as it does not require a water box at the exit of the heat exchanger. This reduces the primary pressure drop and allows the free expansion of the tubes. Thermal loadings are reduced leading to an increased mechanical resistance and an enhanced reliability.

A flow bypass is installed where the venturi is located, between the core exit and the cold leg. It allows a natural convection of the primary fluid during pump shutdown. During normal operation, high flow velocity at the venturi throat leads to a decrease of the local pressure. The cross section area of the venturi throat is designed to balance the pressure between the hot leg (core exit) and the cold leg (heat exchanger-pump module), in order to prevent bypass flow in normal condition. This primary flow layout with a venturi and an integrated heat removal system is issued from the CEA patent N° 92 05220

The decay heat exchanger-pump module can be easily extracted from the reactor vessel once the steam generator has been removed. The pump power supply and the heat exchanger secondary feed-lines are set in the vessel via a removable opening in the upper part of the reactor vessel.