Patent Number: 040381323
Section: summary

BACKGROUND OF THE INVENTION This invention relates to nuclear reactors and nuclear fuel elements for use in nuclear reactors cooled by light or heavy water. The fuel elements for these reactors commonly comprise nuclear fuel rods supported in parallel spaced apart positions in suitably proportioned clusters or bundles so that within the nuclear reactor core, coolant passed over the fuel rods in a direction parallel to their surfaces becomes heated. Thereafter the heated coolant is employed in a heat utilisation plant for example a heat exchanger or a steam turbine. Various proposals have been made for providing an auxiliary means of cooling the nuclear fuel clusters by means of one or more spray cooling tubes which, connected to their own supply of coolant extend within the cluster parallel with the rods, and from holes in the side walls of these tubes, coolant water may be sprayed laterally into the cluster against the rods. The flow of main coolant may thus be supplemented by the auxiliary coolant or replaced by the auxiliary coolant in some circumstances. A difficulty in these arrangements is that only those fuel rods close to a spray cooling tube have a line of sight to it and can readily be reached by the auxiliary coolant. SUMMARY OF THE INVENTION According to the present invention a nuclear fuel element comprising a cluster of nuclear fuel rods supported axes parallel in spaced apart relationship by transverse grids so as to define interspaces for the axial flow of reactor coolant has at least one of the interspaces occupied in part by an axially extending auxiliary coolant conduit with lateral holes through which auxiliary coolant is sprayed into the cluster and deflector means extending from a transverse grid into a position in front of the holes for deflecting auxiliary coolant spray on to parts of the fuel rods inaccessible to auxiliary coolant. The deflecting means preferably include target plates secured to a grid and dependent therefrom into the trajectory of one or more jets of auxiliary coolant emitted from the lateral holes in the conduit. If, as is usual, the fuel rods are disposed axes vertical, in rows on a uniform pitch then the face of the target plate directed towards the auxiliary coolant conduit is bounded by two longitudinal edges spaced by a distance substantially equivalent to the pitch of the fuel rods. When pitched on concentric circles about a central auxiliary coolant conduit the target plate is preferably so disposed that its vertical centre line lies in plane passing through a mid pitch position. If the edges of the target plate are made sharp then there is a well defined deflection of auxiliary coolant and preferably the vertical longitudinal edges of the target plate make acute angles with the face of the plate which is directed towards the auxiliary coolant conduit.