Abstract: A new interface between the cladding and the stack of pellets in a nuclear control rod. According to the invention, an interface joint made of a material transparent to neutrons, in the form of a structure with a high thermal conductivity and open pores, adapted to deform by compression across its thickness, is inserted between the cladding and the stack of pellets made of B4C neutron absorber material over at least the height of the stack. The invention also relates to associated production methods.

Abstract: A control rod for nuclear reactor having a lower section that contains an annular neutron absorber wrapped in a metal sleeve. The sleeve rests on a lower spacer which is seated on the control rod lower end cap. The upper portion of the sleeve extends above the annular neutron absorber of this lower section and is capped by an upper spacer. The standard neutron absorber is supported above this upper spacer which rests on the upper end of the metal sleeve to define a gap between the upper spacer and the annular neutron absorber to accommodate axial expansion.

Abstract: A neutronic reactor comprising an active portion containing material fissionable by neutrons of thermal energy, means to control a neutronic chain reaction within the reactor comprising a safety device and a regulating device, a safety device including means defining a vertical channel extending into the reactor from an aperture in the upper surface of the reactor, a rod containing neutron-absorbing materials slidably disposed within the channel, means for maintaining the safety rod in a withdrawn position relative to the active portion of the reactor including means for releasing said rod on actuation thereof, a hopper mounted above the active portion of the reactor having a door disposed at the bottom of the hopper opening into the vertical channel, a plurality of bodies of neutron-absorbing materials disposed within the hopper, and means responsive to the failure of the safety rod on actuation thereof to enter the active portion of the reactor for opening the door in the hopper.

Abstract: A neutronic reactor comprising an active portion containing material fissionable by neutrons of thermal energy, means to control a neutronic chain reaction within the reactor comprising a safety device and a regulating device, a safety device including means defining a vertical channel extending into the reactor from an aperture in the upper surface of the reactor, a rod containing neutron-absorbing materials slidably disposed within the channel, means for maintaining the safety rod in a withdrawn position relative to the active portion of the reactor including means for releasing said rod on actuation thereof, a hopper mounted above the active portion of the reactor having a door disposed at the bottom of the hopper opening into the vertical channel, a plurality of bodies of neutron-absorbing materials disposed within the hopper, and means responsive to the failure of the safety rod on actuation thereof to enter the active portion of the reactor for opening the door in the hopper.

Abstract: The reactivity of a neutron chain reaction in a nuclear reactor is automatically reduced upon failure of the coolant flow by a system in which nuclear-fuel particles are suspended against gravitational forces by forces of the coolant flow and are in the reactive zone when so suspended. Upon failure of the coolant flow, the particles settle into a space outside the reactive zone and thus do not contribute to the neutron chain reaction and reactivity is reduced.

Abstract: Certain of the nuclear fuel assemblies contained in a fast neutron nuclear reactor core have an integrated passive safety device.More specifically, said device is constituted by an annular block (48) forming at least the lower part of the upper neutron protection (42) of the assembly. The block (48) is formed by elements (50) of a neutron-absorbing material, embedded in a matrix (52) meltable at a temperature above the temperature of the sodium during the normal operation of the reactor. A perforated, inner envelope (54) mechanically secures the block (48), whilst enabling the elements (50) to drop in the assembly following the melting of the matrix (52).

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: A shutdown system for a high temperature nuclear reactor where absorber material elements in the form of balls pass from an elevated reservoir into a vertical channel formed by aligned vertical cavities in horizontal, nose-shaped projections from the side reflector. The balls are transported back to the reservoir by way of a conveyor device. It must be insured that even in the case of accidents the absorber balls arrive in the cavities and that a rapid return of the absorber balls into the reservoir takes place. For the purpose, the reservoir is provided with an automatically-actuated and controllable device for releasing an opening between the reservoir and the vertical channel feed line. Below the channel is a removal tube terminating in a housing and arranged to form a pile of the absorber balls which seals the removal tube. To return the absorber balls, a metering gas acts on the pile and brings the absorber balls to a carrier gas.

Abstract: A gas-cooled high temperature reactor having a core filled with spherical fuel elements is provided comprising a graphite side reflector including at least one nose-like projection comprised of a plurality of graphite nose stones stacked one upon the other, said nose stones each including at least one vertically disposed continuous cavity aligned with at least one vertically disposed continuous cavity in adjacent nose stones, said cavity adapted to receive discrete absorber material elements introduced into the reactor core, said nose stones further including at least one vertically aligned continuous gap which extends into said nose stones from a front portion thereof and is aligned with a corresponding continuous gap in adjacent nose stones, communication between said continuous gap and said cavity being prevented, said nose stones also comprising in top and bottom surfaces thereof sealing means which enable adjacent nose stones to be stacked in a manner sufficient to seal said at least one cavity in a gas-

Abstract: A gas-cooled high temperature reactor is provided having a core filled with spherical fuel elements, in combination with a graphite side reflector including at least one nose-like projection protruding radially into the reactor core from said graphite said reflector, the at least one nose-like projection including at least one vertically disposed cavity adapted to receive discrete absorber material elements introduced into said reactor core as well as a vertically disposed continuous opening which permits communication between said cavity and the core of the reactor, said opening having a maximum width adjacent said cavity which is less than the minimum dimension of said discrete absorber material elements in order to prevent passage of said elements into said continuous opening from said cavity.

Abstract: In a nuclear reactor installation with a small high temperature reactor (26) all of the components of the primary loop, together with the control and shutdown installations (82, 92, 114, 116; 194, 198, 200) are located inside a steel pressure vessel (16) and may be installed and dismantled from above. This makes an economical subterranean construction possible.

Abstract: Gas-cooled nuclear reactors include circulation systems for cooling gas to remove the heat generated in the reactor core. An improved arrangement includes a plurality of steam generators in a horizontal plane located above the horizontal plane of the reactor core. The cooling gas circulates from the bottom of the reactor core to the top. Improved heat removal is accomplished in this manner as the heated cooling gas enters the steam generators after passage through the reactor core without undergoing further circulation in a horizontal or inverse vertical direction.

Abstract: Disclosed is a nuclear power plant comprising a high-temperature pebble bed reactor contained in a cylindrical steel pressure vessel in which an upper part of the cylindrical steel pressure vessel, which contains a heat utilization system, is retracted and equipped with a cover upon which circulating blowers are placed. The heat utilization system comprises, in a known manner, a single steam generator. The steam generator comprises at least two sub-systems independent of one another, with their own distributors and collectors, and with their own inlet and outlet lines. A first shut-down arrangement comprises a plurality of absorber rods insertable into bores of the side reflector from above and comprises rod drives arranged outside the steel pressure vessel in the area of its retracted upper part. A second shut-down arrangement comprises small absorber spheres for introducing into the core of the reactor, and several storage containers and annular conduits for said spheres.

Abstract: A high-temperature nuclear reactor having spherical fuel elements which are rranged approximately ring-shaped about a graphite core, and in particular, a massed-sphere nuclear reactor providing for inherent passive stabilization in the event of damage. The inventive high-temperature reactor of the above-mentioned type distinguishes itself in that the graphite core is formed by a pile or mass of graphite spheres. Through the intermediary of such an axial graphite sphere region, the maximum temperature of the fuel elements of the core can be limited in the event of encountered damage in a manner similar to that as would be the case for a compact graphite column.

Abstract: Device for shutting down a high-temperature nuclear reactor having a reactor core, including a reflector disposed outside the reactor core, channels being disposed in the reflector and having lower ends, storage bins being disposed above the reactor core and being in communication with the channels above the lower ends thereof, a neutron-absorbing material formed of fluidic bodies being storable in the storage bins and feedable into the channels, a plurality of lines connected between the lower ends of the channels and the storage bins, means for selectively establishing an upwardly directed fluid flow of the material in one of the plurality of lines for conveying the neutron-absorbing material at a given adequate speed from one of the channels into one of the storage bins.

Abstract: Pebble-bed nuclear reactor capable of being shut down by a fluidized mass of bodies containing neutron-absorbing material, the fluidized mass of bodies being received in a storage container disposed above the pebble bed during normal operation of the reactor, the storage container being formed with a closable discharge opening, including a piston rigidly connected to the storage container and disposed below the discharge opening thereof, the piston being guided in a cylinder stationary relative to the reactor and being open at the top thereof, the storage container being displaceable in vertical direction between upper and lower end positions thereof, the piston, in the upper end position of the storage container, closing off the cylinder at the upper edge located at the open top of the cylinder and, in the lower end position of the storage container, the fluidized mass of bodies discharged from the discharge opening of the storage container being formed on top of the piston into a discharge cone having a hei

Abstract: The nuclear reactor control column comprises a column disposed within the nuclear reactor core having a variable cross-section hollow channel and containing balls whose vertical location is determined by the flow of the reactor coolant through the column. The control column is divided into three basic sections wherein each of the sections has a different cross-sectional area. The uppermost section of the control column has the greatest cross-sectional area, the intermediate section of the control column has the smallest cross-sectional area, and the lowermost section of the control column has the intermediate cross-sectional area. In this manner, the area of the uppermost section can be established such that when the reactor coolant is flowing under normal conditions therethrough, the absorber balls will be lifted and suspended in a fluidized bed manner in the upper section.