Abstract: A process is provided for the long term shutdown of a high temperature nuclear reactor comprised of a pile of spherical fuel elements in a core by means of a neutron absorbing absorber material wherein the absorber material consisting of spherical absorber elements is introduced in the core of spherical fuel elements in the form of a column, but wherein the intermixing of the absorber material with the fuel elements is prevented. An apparatus for practicing the process is also provided comprised of a graphite side reflector concentrically surrounding a circular cylindrical core filled with a pile of spherical fuel elements of a high temperature nuclear reactor, into which at least two nose shaped projections distributed uniformly about the circumference radially project, with each of the projections comprising a vertical cavity to contain the absorber material. The vertical cavity is located in the vicinity of the core in the area of the frontal side facing the core of each projection.

Abstract: Disclosed is a process for reloading the contaminated empty reactor cavity of a nuclear reactor with spherical operating elements forming the core of a high temperature reactor comprising supplying the operating elements to the reactor cavity first through a central loading tube in the roof reflector of the nuclear reactor to a predetermined load level, the loading tube being extended at the onset of the loading process toward the floor reflector and being adjusted upwardly during continued loading with the rising load level and after reaching the predetermined load level, supplying further operating elements through a plurality of auxiliary loading tubes in the roof reflector of the nuclear reactor in concentric circles about the central loading tube with the loading sequence proceeding circle after circle beginning with the circle closest to the central loading tube.

Abstract: Improvements in high temperature gas cooled nuclear reactors is effected by an arrangement of paired absorber elements, each pair comprising a rod shaped absorber element and a tubular absorber element generally surrounding the rod shaped element. With this paired combination in a reactor employing spherical fuel elements, the effective life of the absorber rods is significantly extended by protection of the rod shaped absorber element from excessive amounts of irradiation from thermal neutrons.

Abstract: Disclosed are a method and apparatus for regulating and shutting down a gas cooled nuclear reactor having a bed of spherical fuel elements, wherein regulation of the reactor is accomplished by a first set of absorber rods in the side reflector of the reactor, partial shutdown is achieved by a second set of absorber rods movable in the top reflector and in the space above the fuel elements, and total shutdown is accomplished by a third independent set of absorber rods which can be moved downwardly into the fuel elements.

Abstract: The core pile of a gas-cooled nuclear reactor is controlled by a plurality of absorbent graphite rods that are inserted into the pile according to a pre-determined pattern, the pattern being such that the density of distribution of the control rods over the cross-sectional area of the core pile is radially increased in the direction of the core periphery. By this control rod arrangement an overly severe concentration in the flow of neutrons on the periphery of the cord pile is avoided, and a more even distribution of neutron flow across the diameter of the reactor is obtained.