Patent Number: 039765431
Section: claims

1. A temperature actuated shutdown assembly for a nuclear reactor comprising a neutron absorber, a tube disposed around said absorber and coaxial with the longitudinal axis of the absorber, said tube having a plurality of ports therein spaced around its circumference, a flange welded to the tube concentrically over each port, a bimetallic disk retained movably within each flange in the shape of a spherical cap with its inner, normally convex side composed of a layer of metal and its outer, normally concave side composed of a layer of a different metal of a higher coefficient of thermal expansion, a metal ball retained in the center of the inner layer of each disk by a retainer with the center of said metal ball aligned concentrically with and projecting partially through the port in the side of the tube thereby supporting said absorber, said metal ball being biased inwardly toward said absorber, whereby upon reaching a preset temperature, stresses will be created within at least one of the bimetallic disks; the imbalanced thermal stresses will cause at least one disk to reverse concave and convex sides thus removing the ball from the hole in the wall of the tube allowing the absorber to drop into the reactor core. 2. The combination of claim 1 wherein the outer layer of each bimetallic disk is made of stainless steel, the inner layer is made of molybdenum and the ball is made of cobalt alloy tool material. 3. The combination of claim 1 wherein the outer layer of the bimetallic disk is made of a nickel-chromium-iron alloy, and the inner layer is made of molybdenum-titanium alloy. 4. The assembly of claim 1 including means responsive to reactor power for generating heat disposed in each bimetallic disk whereby said generating means in response to an increase in reactor power will cause at least one disk's temperature to increase to the preset temperature where imbalanced thermal stresses in the disk will cause the disk to reverse conical and convex sides. 5. The heat generation means of claim 4 wherein the means is comprised of a foil of fissionable metal disposed in the bimetallic disk between the two layers thereof. 6. The heat generation means of claim 4 wherein the means is comprised of discrete nodules of an oxide of a fissionable metal dispersed within at least one of the layers of the bimetallic disk. 7. A temperature actuated shutdown assembly for a liquid metal cooled nuclear reactor comprising a hexagonal absorber rod, a hexagonal tube disposed around said absorber rod and coaxial with the longitudinal axis of the absorber rod, said tube having three ports therein located in alternate sides of the hexagonal tube, a round "L" shaped flange welded to the tube side concentrically over each of said ports, a bimetallic disk within each flange shaped as a spherical cap with the normally concave outer side of the disk composed of stainless steel and the normally convex inner side composed of molybdenum, means responsive to reactor power for generation of heat within said bimetallic disk, a helical spring trapped compressively between each flange and each disk and urging said disk toward the tube, a cobalt alloy tool material ball retained in a spherical depression in the center of the inner layer of each said disk by a retainer formed of the material of the inner layer, the bimetallic disks being retained movably against the sides of the hexagonal tube by the circular flanges with the centers of the cobalt alloy tool material balls aligned concentrically with and projecting partially through the ports in the sides of the hexagonal tube supporting a conical bottom of said absorber rod, whereby upon reaching a liquid metal coolant temperature in the range of 550.degree.C. to 770.degree.C., a condition of imbalanced, thermally induced stresses will be created within at least one of the bimetallic disks as a result of the differing thermal coefficients of expansion of the two composite metals; the imbalanced thermal stresses will cause at least one bimetallic disk to reverse concave and convex sides thus removing the ball from the hole in the side of the hexagonal tube allowing the absorber rod to slip towards the removed ball or balls thus clearing the unremoved balls or ball and dropping into the reactor core thus depressing reactor power.