Patent Number: 041949480
Section: summary

BACKGROUND OF THE INVENTION The present invention relates generally to nuclear reactor systems and, more particularly, to a locking device for supporting and locking fuel assemblies in place upon a support plate in a gas cooled reactor. In gas cooled reactors, a reactor core is formed with a number of fuel assemblies containing fissile and/or fertile materials serving as a source of heat. A coolant gas such as helium, for example, is circulated between the reactor core and heat exchanger means in order to remove heat from the reactor core and employ it for doing useful work. Within such reactors, the fuel assemblies are commonly formed as elongated tubular members which are suspended from a support plate or grid in order to facilitate circulation of the coolant gas through the fuel assemblies. In gas cooled reactors of the type referred to above, the fuel assemblies are commonly installed and removed from beneath the grid or support plate so that the fuel assemblies must be firmly anchored to or secured upon the plate. In addition, it is necessary to assure against the fuel assemblies dropping from the support plate under normal operating conditions as well as under abnormal conditions caused for example by a seismic occurrence. Normal forces acting upon fuel assemblies supported in such a gas cooled reactor include: (a) downward force tending to separate the fuel assembly from the support plate resulting from the weight of the fuel assembly itself, (b) additional downward separating force resulting from a pressure drop caused by downward flow of coolant gases through the fuel assembly, and (c) possible vibratory effects of the coolant gas flow acting upon the fuel assembly. Abnormal forces acting upon the heat fuel assembly which must also be resisted in order to firmly secure the fuel assembly in place upon the support plate include: (a) Lateral forces resulting from relative horizontal acceleration between the respective fuel assemblies and the support plate such as may be caused for example by seismic effects, and (b) Upward and/or downward forces caused for example by vertical acceleration which may also result for example from a seismic occurrence. Accordingly, there has been found to remain a need for a suitable locking device capable of supporting and locking such fuel assemblies in place within bores formed in a support plate while resisting forces of the type referred to above. SUMMARY OF THE INVENTION It is accordingly an object of the invention to provide a locking device for supporting and locking fuel assemblies in place in bores of a support plate, the device being capable of overcoming problems of the type referred to above while facilitating removal and/or replacement of the fuel assemblies upon the support plate. The locking device preferably includes a sleeve arranged between the fuel assembly and a receiving bore of the support plate, the sleeve including upwardly extending fingers arranged in wedged engagement between an annularly tapered surface on the fuel assembly and the bore of the support plate, the sleeve also having downwardly extending fingers arranged in wedged engagement between a tapered surface of the bore and the surface of the fuel assembly, the sleeve interacting with the fuel assembly and support plate bore so that the fuel assembly is supported therein by its own weight. Preferably, the downwardly extending fingers are pre-stressed in a radial direction to facilitate removal and/or insertion of the fuel assembly within the bore. Additional means are also preferably provided to resist undesired upward movement of the fuel assembly within the bore, for example, upon the occurrence of a seismic event in order to prevent undesired disengagement of the sleeve from between the fuel assembly and the support plate bore. Seal means may also be employed in conjunction with the sleeve to restrict and adjust the flow of coolant gases past and through the fuel assembly. Additional objects and advantages of the invention are made apparent in the following description having reference to the accompanying drawings.