Patent Number: 046831169
Section: claims

1. A non-controlled nuclear fuel assembly which is not penetrated by control rods during operation of a nuclear reactor in whose core said non-controlled nuclear fuel assembly is contained; the said nuclear fuel assembly including a top nozzle, a bottom nozzle, a plurality of nuclear fuel rods extending between said nozzles, a plurality of grids extending along said fuel rods for maintaining said fuel rods positioned between said nozzles, and structural members, each of which is a hollow tube, secured to said top and bottom nozzles for forming said assembly into an integral unit, the said assembly being characterized by structural members of substantial thickness and at least certain of which contain burnable neutron absorbers. 2. A nuclear reactor including a core having a plurality of fuel assemblies, each of said fuel assemblies having a top nozzle, a bottom nozzle, nuclear fuel rods interposed between said nozzles, grids spaced along said nozzles in engagement with said fuel rods to position said fuel rods, some of said fuel assemblies having thimbles, the thimbles of said some fuel assemblies being secured to said top nozzle and to said bottom nozzle for forming an integrated unit of each of said some assemblies, control rods associated only with said some assemblies, moveable in and out of said thimbles for controlling the operation of said reactor, at least certain of other than said some fuel assemblies having no thimbles at least at some of the locations where said some of said assemblies have thimbles, said other assemblies having tubular members at some of said no-thimble locations secured to said top nozzle and to said bottom nozzle for forming said each of said other fuel assembly into an integrated unit, at least some of said tubular members containing burnable neutron absorbers. 3. The reactor of claim 2 wherein the tubular members have a substantially greater wall thickness than the thimbles. 4. The reactor of claim 5 wherein each of the other than the some assemblies has fewer tubular members than the some assemblies have thimbles and wherein there are locations in said other assemblies, corresponding to the location occupied by thimbles in said some assembies in which there are no thimbles and no tubular members, and wherein there are fuel rods in the no-thimble no-tubular-member locations in said each of said other assemblies whereby there are a greater number of fuel rods in said other fuel assemblies than in said some fuel assemblies.