The invention relates to a device for fixing two parts with a captive screw and the corresponding fixing process.
In pressurized water nuclear reactors, the core consists of a group of prismatic fuel assemblies arranged vertically and side by side and generally surrounded by a peripheral partitioning which matches the outer shape of the core. This partitioning makes it possible in particular to hold the core assemblies and to channel water under pressure toward the base of the core before it passes upwards through the latter. The partitioning of the core of a pressurized water nuclear reactor generally comprises a set of vertical plates assembled at right angles and holding devices consisting of horizontal plates cut out in accordance with the shape of the core section and inserted between the set of vertical partitioning plates and the core enclosure.
During the operation of the reactor, interstices can appear between the vertical plates forming the partitioning wall, with the result that water under pressure can pass in the form of jets from the space situated between the core enclosure and the partitioning into the volume occupied by the core and bounded by the partitioning. In fact, there is a difference in the pressure of the cooling water between the outside and the inside of the core, produced by the pressure drop inside the assemblies forming the core. The pressurized jets directed from the exterior to the interior of the core cause vibrations of the rods in the peripheral assemblies of the reactor core, which are highly damaging to the behavior of these assemblies in service, the damage being capable of extending even to a rupture of fuel rods.