Patent Number: 
Section: claims

1. A nuclear control rod extending along a longitudinal direction (XX′), comprising a plurality of pellets, made of boron carbide B4C neutron absorber material, stacked on each other in the form of a column and a cladding surrounding the column of pellets, in which, the cladding and the pellets have a circular cross-section transverse to the longitudinal direction (XX′), and in which an interface joint, also with a circular cross-section transverse to the longitudinal direction (XX′), made of a material transparent to neutrons and is inserted between the cladding and the column of stacked pellets, at least over the height of the column, in which the interface joint is a structure, mechanically decoupled from the cladding and from the column of pellets, with a high thermal conductivity and open pores, adapted to deform by compression across its thickness so as to be compressed under the effect of the three-dimensional swelling of the pellets under irradiation, the initial thickness of the joint and its compression ratio being such that the mechanical load transmitted to the cladding by the pellets under irradiation remains less than a predetermined threshold value characterized in that the interface joint is made from a braid comprising a plurality of carbon fibre layers and a plurality of layers comprising silicon carbide fibres superposed on the carbon fibre layers. 2. The nuclear control rod according to claim 1, in which the open pores of the interface joint have a volume equal to at least 30% of the total volume of the interface joint as produced in fabrication. 3. The nuclear control rod according to claim 2, in which the open pores of the interface joint have a volume between 30% and 95% of the total volume of the interface joint as produced in fabrication. 4. The nuclear control rod according to claim 3, in which the open pores of the interface joint have a volume between 50% and 85% of the total volume of the interface joint as produced in fabrication. 5. The nuclear control rod according to claim 1, in which the thickness of the interface joint in its section transverse to the (XX′) direction is more than at least 10% of the radius of the pellets. 6. The nuclear control rod according to claim 1, in which the interface joint has a volume percentage of fibres between 15 and 50% and the open pores of the interface joint have a volume between 50% and 85% of the total volume of the interface joint as produced in fabrication. 7. The nuclear control rod according to claim 1, for a gas-cooled fast reactor (GFR), in which the basic material of the cladding is a refractory ceramic matrix composite (CMC) and the absorber pellets are made of B4C. 8. The nuclear control rod according to claim 1, for a sodium-cooled fast reactor (SFR), in which the cladding is made of a metallic material, and the absorber pellets are made of B4C. 9. The nuclear control rod according to claim 1, for Pressurized Water Reactors (PWR), or Boiling Water Reactors (BWR) in which the cladding comprises a refractory ceramic matrix composite CMC material and the absorber pellets are made of B4C. 10. Nuclear absorber assembly comprising a plurality of the nuclear control rods according to claim 1, and arranged to form a lattice. 11. A control rod according to claim 7, wherein the refractory ceramic matrix composite is SiC—SiCF.