Abstract: In a device for monitoring the atmosphere within the containment shell (1) of a reactor plant, a sample removal means (41) is provided in the containment shell, from which a gas mixture is led via a measuring line (42) through a measuring zone (14) and subsequently discarded. The concentration of the gas is reduced upstream of the measuring zone (14) in a dilution plant (40).

Abstract: The additional mixing grid has no belt and comprises at least two sets of crossed plates that are fixed to each other at their cross-points, the plates being fitted with fins for stirring the coolant, and delimiting cells, some for receiving guide tubes and the others for receiving fuel rods. Each plate is provided, on each of the faces of those internal cells that receive the rods, with bosses that project sufficiently little to leave radial clearance for the rods passing through the cells and the projection of the bosses is proportioned relative to the projection of the fins so that in the event of bending vibration the rods come into contact with the bosses without reaching the fins, the lengths of the plates being such that the footprint of the additional grid is less than the footprint of the polygon constituting the virtual envelope of the rods.

Abstract: A bracing grid suitable for use in a light water reactor has a plurality of mutually intersecting sets of plates defining cells which receive fuel rods. The plates carry springs for retaining the rods by friction. Each spring is formed has a U legs located each on one side of a plate, the branch being for contact on the elements in two mutually adjacent cells separated by the plate. The two legs are connected by a loop straddling the plate and are connected to each other by a weld at the base of the loop, through a window formed through the plate. The legs of each spring are also mutually connected by mechanical locking means which retain the two legs with respect to each other and with respect to the respective plate.