| abstract |
Certain of the nuclear fuel assemblies contained in a fast neutron nuclear reactor core have an integrated passive safety device. n More specifically, said device is constituted by an annular block (48) forming at least the lower part of the upper neutron protection (42) of the assembly. The block (48) is formed by elements (50) of a neutron-absorbing material, embedded in a matrix (52) meltable at a temperature above the temperature of the sodium during the normal operation of the reactor. A perforated, inner envelope (54) mechanically secures the block (48), whilst enabling the elements (50) to drop in the assembly following the melting of the matrix (52). |