Control cluster including demountable fuel for a nuclear fuel assembly

Control cluster including demountable cylindrical rods comprising a crosspiece constituted by a plurality of fins disposed angularly in relation to one another and each comprising at least one protective tube having a blind bore which is internally threaded over a part of its length, an axis of said bore extending in a longitudinal direction of said control cluster, as well as a set of cylindrical rods each comprising an active part and an end part adapted to be engaged and fixed in said bore of a said protective tube and comprising, in an axial extension of a plug for closing said active part, a connecting part which is threaded over a part of its length to enable screwing of said rod into the bore of a corresponding protective tube, wherein, for each one of said demountable rods:

• (a) the end part of said protective tube is open towards the exterior and comprises a reduced external diameter part over a certain length and at least one seat on a wall of said protective tube for seating said rod, and openings through its wall in said reduced diameter part;
• (b) said end part of said rod is integral with a ferrule which is coaxial with said rod and which surrounds said connecting part of said rod over a portion of its length corresponding to said portion engaged in said reduced diameter part of said protective tube, said ferrule having an internal diameter substantially equal to said reduced diameter of said protective tube and being engaged on said reduced diameter part of the protective tube;
• (c) a prismatic engagement surface is provided on said external surface of said rod;
• and
• (d) said rod is locked in said protective tube by deformed parts of said ferrule housed within said openings of said end part of said protective tube.