| 摘要 |
<p>The invention relates to an improved gray rod for insertion in a nuclear fuel assembly having an array of fuel rods. The gray rod includes a thin-walled cladding tube (46) a first longitudinal section of which is positioned within, and a second longitudinal section of which is positioned essentially without, the array of fuel rods when the gray rod is inserted in the fuel assembly. The first longitudinal section defines a pellet-receiving space (52) having detained therein a stack of annular pellets (48) with an outer diameter sufficient to lend radial support to the wall of the first longitudinal tube section. The second longitudinal section defines a hollow space (54) devoid of pellets and having means to resist radial collapse under external pressure. This means may be a partially compressed spiral spring (50) which serves the dual purpose of retaining the stack of pellets (48) in the pellet-receiving space (52) and of lending radial support to the wall of the second longitudinal tube section or it may be holes through the wall to allow pressure equalisation (Fig. 6, not shown). The cladding tube is composed of stainless-steel material having a low neutron-capture cross- section, and the annular pellets preferably being composed of Zircaloy or Zirconia material. <IMAGE></p> |
