Abstract: A modular lining for adapting the containment to the core of a pressurized water nuclear reactor, consisting of juxtaposed modular blocks (5) placed between the core containment (1) and the outer surface of the core (3). Arranged between the adjacent faces of the blocks (5), there are thin packing pieces (8) maintaining a certain gap between the undrilled solid blocks (5). The blocks (5) are fixed non-contiguously to the core containment (1) by screw devices (10) cooled by water circulation. The invention applies in particular to pressurized water nuclear reactors of improved efficiency and with a varying neutron spectrum.

Abstract: Fuel array for an undermoderated nuclear reactor, comprising rods (6) arranged in a prism-shaped casing (1) parallel to the height of this casing (1). The internal surface of each of the walls (2) of the casing (1) is provided with channels (5) each of the channels (5) is located opposite a rod (6) arranged at the periphery of the array. The projecting parts (9) of the walls (2), between two channels (5), occupy part of the space between two peripheral rods (6). In this way, the moderating level remains constant throughout the cross-section of the array.The invention applies, in particular, to pressurized water reactors.

Abstract: A complementary shutdown device for an undermoderated nuclear reactor, comprising, inside certain arrays (3) of the core, guide tubes (7) of which the cross-section is at least equal to the sum of the cross-sections of three rods (6), and which are surrounded by at least one row of fertile rods (8), and a set of shutdown rods, the cross-section of which matches the cross-section of the guide tubes (7). The shutdown is obtained by allowing the shutdown rods, containing a neutron-absorbing material, to fall into the arrays (3) of the core, in the position of maximum insertion. The invention applies, in particular, to pressurized water nuclear reactors.

Abstract: Upper internal equipment of a pressurized water nuclear reactor, comprising guide tubes containing guide plates and sleeves adapted to two different types of charge of the reactor core, one for obtaining a thermal neutron spectrum and the other for obtaining an epithermal spectrum. The plates (20) and the sleeves (33, 34) have, for each of the guide tubes, a first set of perforations (31, 36) and a second set of perforations (30,35) for guiding the control rods in either case. The invention applies to a pressurized water reactor operating either as a conventional reactor or as an undermoderated reactor.