Patent Number: 039363503
Section: claims

1. A nuclear reactor, including an upstanding vessel, a reactor core comprising a plurality of assemblies of elongated fuel rods housed within the vessel, and means within the vessel for supporting the fuel rods at a plurality of locations along the longitudinal dimension of the rods for maintaining the rods in a predetermined structural arrangement within the vessel, wherein the support means is constructed to have a measure of thermal expansion under designed reactor operating temperatures at each of the support locations along the rods substantially equal to the thermal expansion of the support means at the other support locations providing support in a parallel plane within the reactor vessel, thus balancing the thermal expansions along parallel planes of support at the plurality of support locations to substantially retain alignment of core components. 2. The reactor of claim 1 wherein said support means comprises a bottom support plate for supporting said core positioned laterally across one end of the fuel rods and a core hold down plate for supporting said core positioned laterally across the other end of the fuel rods, said bottom support plate and core hold down plate providing support for the fuel rods along parallel planes and being supported in position from a wall of the vessel. 3. The nuclear reactor of claim 1 including means for controlling the reactivity of the core wherein the control means is slidably mounted to be movable into and out of the core along an axis parallel with the longitudinal dimension of the rods and is supported in alignment with the rods by the support means. 4. The nuclear reactor of claim 3 having an open ended vessel enclosed by a top plug having penetrations into and through which the control means extend wherein the top plug is constructed to have a measure of thermal expansion in a given plane under designed reactor operating temperatures substantially equal to the thermal expansion of the support means along parallel planes to the given plane along which the support means provide support for the control means.