GB1361700A - Nuclear fuel assembly - Google Patents

Abstract

1361700 Fuel elements COMMISSARIAT A L'ENERGIE ATOMIQUE 11 Aug 1972 [12 Aug 1971] 37615/72 Heading G6C A nuclear fuel assembly for use in a sodiumcooled fast reactor comprises at least one bundle of elongate fuel pencils disposed parallel to one another within a shroud, the shroud consisting of two sections 34, 36 disposed end-to-end and connected by a joint allowing angular displacement of the sections relative to one another. The assembly illustrated in Fig. 1, comprises two superposed bundles, the pencils 20 in the lower bundle being of the "integrated" kind (i.e. containing a fission gas collection chamber in region 22, a column of pellets of fertile material in region 24, a column of pellets of fissile material in region 26, and finally a space allowing the latter column to expand upwards) and borne by a grid 21 while the pencils 30 in the top bundle, which are suspended from a grid 32, are filled with pellets of fertile material. The top section 36 of the shroud may be thinner than the bottom section 34 and slightly overlaps this latter section at its lower end while enclosing an annular neutron shield 18 at its upper end. The two sections are connected to one another by a rod 38 provided with a gripping head 40 and replacing the central fertile pencil in the top bundle. The rod 38 is secured by three fins 42 to the upper end of section 36 and by three fins 44 to the upper end of section 34. In order that the rod 38 can bend freely, without contacting fertile pencils, it is surrounded by a thin jacket 46 of hexagonal cross-section. The rod 38 may be replaced by a tube which takes the place of not one but seven fertile pencils. With either of these arrangements, the deformation under irradiation shown by the dashed line for a unitary shroud is reduced to the amount shown by the chain-dotted line. In alternative embodiments, the fuel assembly is limited to a single bundle of "integrated" pencils housed in the bottom section of the shroud (Fig. 2, not shown) and the two sections of the shroud are connected by a flexible toroidal diaphragm (Fig. 3, not shown). In further embodiments, the two sections are connected by a ball and socket joint provided with a labyrinth seal (Fig. 4, not shown), or by a Cardan joint in which case sealing-tightness is obtained by thin metal plates secured to one section and pressed against the other section by the pressure of the coolant flowing through the shroud (Fig. 5, not shown). In yet another embodiment (Fig. 6, not shown), the two sections are connected by a rod in two parts joined by a ball and socket joint and each secured to one of the sections.