Patent Number: 052767213
Section: summary

The invention relates to a nuclear reactor fuel assembly, having two end plates with inner and outer surfaces, elongated fuel rods being filled with nuclear fuel, being disposed between the inner surfaces and having longitudinal axes perpendicular to the inner surfaces, and a leaf spring disposed on the outer surface of one end plate and bent at an acute angle, the leaf spring having a first leg substantially perpendicular to the outer surface of the one end plate and loosely engaged in an elongated guide groove in the one end plate, and a second leg having a longitudinal orientation defining a plane along with the longitudinal orientation of the first leg and the longitudinal orientation of the guide groove, the second leg meeting the outer surface of the one end plate at an acute angle and being rigidly secured by an end of the second leg to the outer surface of the one end plate. The structure described above is a conventional kind of fuel assembly. It is disposed in a nuclear reactor with the fuel rods oriented vertically. The lower end plate rests on a lower core grid inside the nuclear reactor, while an upper core grid plate, that is parallel to the lower core grid plate, rests on the leaf spring, at the apex of the acute angle formed by the leaf spring, and the fuel assembly presses against the lower core grid plate, deforming the leaf spring. Such a construction gives the fuel assembly a resiliently stable seat between the lower and upper core grid plates. In the nuclear reactor, the fuel assembly experiences a flow of coolant longitudinally from bottom to top, and the fuel assembly then has a tendency to float in the flow. Its floating is prevented by the force of the leaf spring on the outer surface of the upper end plate of the fuel assembly. However, a coolant flow through the fuel assembly that considerably increases the tendency of the fuel assembly to float can occur later, as a result of later changes in the external primary system that follows the nuclear reactor. Under some circumstances, the spring force exerted on the fuel assembly by the leaf spring may then no longer be adequate to prevent such floating. It is accordingly an object of the invention to provide a nuclear reactor fuel assembly, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and which does so in such a way that it is prevented from floating even in intensified coolant flows inside a nuclear reactor. With the foregoing and other objects in view there is provided, in accordance with the invention, a nuclear reactor fuel assembly, comprising two end plates having inner and outer surfaces; elongated, nuclear fuel-filled fuel rods being disposed between the inner surfaces and having longitudinal axes perpendicular to the inner surfaces; a leaf spring being disposed on the outer surface of one of the end plates and being bent at an acute angle defining first and second legs, the first leg being substantially perpendicular to the outer surface of the one end plate and loosely engaged in an elongated guide groove formed in the one end plate, the second leg meeting the outer surface of the one end plate at an acute angle and having an end rigidly secured to the outer surface of the one end plate, the first and second legs and the guide groove having longitudinal orientations together defining a plane; and a supplementary spring being bent at an acute angle and disposed between the legs of the leaf spring, the supplementary spring having one end loosely engaged in the guide groove and another end is loosely guided on the first leg of the leaf spring. The supplementary leaf spring acts parallel to the leaf spring and thus reinforces the spring force acting counter to the flow of the coolant in the nuclear reactor. The supplementary spring is also especially well-suited for retrofitting fuel assemblies that are already in use in a nuclear reactor. Other features which are considered as characteristic for the invention are set forth in the appended claims. Although the invention is illustrated and described herein as embodied in a nuclear reactor fuel assembly, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.