Abstract: Methods and systems for stabilizing spent fuel assemblies from sodium-cooled nuclear reactors using Zamak are described herein. It has been determined that there is a synergism between Zamak and sodium that allows Zamak to form thermally-conductive interface with the sodium-wetted surfaces of the fuel assemblies. In the method, one or more spent fuel assemblies are removed from the sodium coolant pool and placed in a protective sheath. The remaining volume of the sheath is then filled with liquid Zamak. To a certain extent Zamak will dissolve and alloy with sodium remaining on the fuel assemblies. Excess sodium that remains undissolved is displaced from the sheath by the Zamak fill. The Zamak is then cooled until solid and the sheath sealed. The resulting Zamak-stabilized spent fuel assembly is calculated to have sufficient internal thermal conductivity to allow it to be stored and transported without the need for liquid cooling.

Abstract: The invention relates to the field of nuclear technology. A container for storing, transporting and disposal of solid radioactive waste comprises a cask made of reaction-sintered silicon carbide comprising free silicon in an amount of 3-30 wt. % with a layer of gas-phase silicon carbide deposited on the surface thereof. The outer layer of the cask is made of a metal foam with an open porosity of 60-70% and a pore size of 5-6 mm; the pores are filled with boron carbide powder having a dispersity of 40-50 ?m, which protects the environment from nuclear radiation emitted by HLW. A canister made of stainless steel with a thickness of 1-1.5 mm and intended for receiving radioactive waste is placed inside the silicon carbide cask. A 5 mm gap between the inner surface of the silicon carbide cask and the stainless-steel canister is filled with boron carbide powder which protects the environment from nuclear radiation emitted by HLW.

Abstract: A nuclear reactor core mechanical support bracket is disclosed. The support bracket includes a housing, a spring disposed internally within the housing, a shaft slidingly disposed within the housing, a shaft travel pin, and a flange. The shaft is configured to engage the spring to compress and decompress the spring as the shaft travels in and out of the housing. The shaft travel pin controls the travel of the shaft. The flange is configured to mount the nuclear reactor core mechanical support bracket to a canister of a nuclear reactor. The shaft includes an inset configured to interface with a nuclear reactor core component.

Abstract: A method for simulating the flow of a fluid in a vessel of a nuclear reactor is provided. The nuclear reactor includes the vessel and a core inside the vessel, the core including nuclear fuel assemblies, each one extending in an axial direction, including nuclear fuel rods and a grid for maintaining the rods, and being spaced apart from another by a clearance between the grids in a transverse direction. This method for simulating a fluid flow in the vessel of a nuclear reactor includes determining of head loss coefficients in the core, and computing the fluid pressure and speed component(s) in the core using the equation: ?P=?K×V where P is the component of the fluid pressure, K is a matrix including the determined head loss coefficients, and V is a vector including the fluid speed component(s).

Abstract: Disclosed is a filter including a second layer disposed between a first layer and a third layer. The first layer is composed of iron. The second layer is composed of 1 part by volume of lithium fluoride, 20 to 50 parts by volume of aluminum, and 50 to 80 parts by volume of aluminum fluoride. The third layer is composed of 1 part by weight of lithium fluoride and 99 to 100 parts by weight of magnesium fluoride.

Abstract: The neutron irradiation apparatus includes an introduction tube for introducing a proton beam, a target structure provided in a lower end of the introduction tube, an aluminum fluoride layer disposed below the target structure in an irradiation path of neutrons generated in the target structure, and a heavy water layer placed under the aluminum fluoride layer in layers. The aluminum fluoride layer is set at a thickness that increases epithermal neutrons. Since use of only the aluminum fluoride layer increases its thickness too much, heavy water is placed. Heavy water moderates neutrons quickly, and allows increasing epithermal neutrons without increasing the thickness. The combination of the aluminum fluoride layer and the heavy water layer allows increasing epithermal neutrons by attenuating only fast neutrons without increasing thermal neutrons. Accordingly, neutron flux with many epithermal neutrons is obtained.

Abstract: A heavy radial neutron reflector for a pressurized water reactor that employs elongated lengths of round bar stock closely packed in either a triangular or rectangular array extending between former plates of a core shroud between the core barrel and the baffle plates which outline the periphery of the reactor core and are formed in axial and circumferential modules. Flow channels are formed in the long gaps between the adjacent round bar stock that communicates cooling water that enters through the core barrel at the top of the shroud and flows down through openings in the former plates to the bottom of the neutron reflector where it exits through a lower baffle orifice to join other cooling water flowing up through the lower core support plate.

Abstract: An integral pressurized water nuclear reactor for the production of steam utilizing a helical coil steam generator, a plurality of internal circulation pumps, and an internal control rod drive mechanism structure.

Abstract: A heavy radial neutron reflector for a pressurized water reactor that employs elongated lengths of round bar stock closely packed in either a triangular or rectangular array extending between former plates of a core shroud between the core barrel and the baffle plates which outline the periphery of the reactor core and are formed in axial and circumferential modules. Flow channels are formed in the long gaps between the adjacent round bar stock that communicates cooling water that enters through the core barrel at the top of the shroud and flows down through openings in the former plates to the bottom of the neutron reflector where it exits through a lower baffle orifice to join other cooling water flowing up through the lower core support plate.

Abstract: A lower internals nuclear reactor structure having a tubular core barrel with an upper and lower open end, coaxially supported therein. A reflector having an outside curvature that substantially matches the curvature of the inside surface of the core barrel and substantially contacts the inside surface substantially over an axial length of the core, is fixedly connected to the inside surface of the core barrel at a plurality of axial and circumferential locations to be substantially supported by the inside surface of the core barrel.

Abstract: A boiling water reactor has a core disposed in the reactor pressure vessel and loaded with a plurality of fuel assemblies including transuranic nuclides. A ratio of Pu-239 in all of the transuranic nuclides included in the fuel assembly, which is loaded in the core, with a burnup of 0 is 3% or more but 45% or less. In the fuel assembly having a channel box and a plurality of fuel rods disposed in the channel box, a transverse cross section of a fuel pellet in the fuel rod occupies 30% or more but 55% or less of a transverse cross section of a unit fuel rod lattice in the channel box.

Abstract: A nuclear reactor module includes a reactor core and a reactor housing that surrounds the reactor core about its sides, wherein the reactor housing is configured to direct coolant through the reactor core. A neutron reflector is located between the reactor core and the reactor housing, wherein the neutron reflector has a plurality of inlet ports facing the reactor core. The neutron reflector also has a plurality of outlet ports fluidly connected to the inlet ports to direct a portion of the coolant through the neutron reflector.

Abstract: Among other things, an apparatus includes a combination of a fissionable material, a molten salt, and a moderator material including one or more hydrides, one or more deuterides, or a combination of two or more of them.

Abstract: Reactor component adapted to be used in fission reactors comprising a core (2) consisting of a first material and a layer (3) consisting of a second material. The layer (3) encloses at least partly the core (2). The reactor component is characterized in that the component (1) comprises and intermediate layer (4) between the core (2) and the layer (3). The intermediate layer (4) has a material gradient that comprises a decrease of the concentration of the first material from the core (2) to the layer (3) and an increase of the concentration of the second material from the core (2) to the layer (3).

Abstract: The invention concerns a control rod configured for a nuclear power light water reactor of the BWR or PWR kind. The control rod contains absorber material. At least 50%, with respect to weight, of the absorber material that is in the control rod is in the form of hafnium hydride. The invention also concerns the use of such a control rod during operation in a nuclear power light water reactor of the BWR or PWR kind.

Abstract: A control rod for a nuclear boiling water reactor is described. The control rod has a longitudinal centre axis and control rod blades, each control rod blade having a first and a second side and being substantially parallel to the longitudinal center axis. Each control rod blade comprises an absorber material which extends from a first absorber end to a second absorber end, the distance between the first absorber end and the second absorber end defining an active length. The control rod blades are provided with distance means on the first and second sides of the control rod blades, the distance means extending a distance of at least a third of the active length of the control rod blade.

Abstract: In a nuclear reactor neutron panels varying in thickness in the circumferential direction are disposed at spaced circumferential locations around the reactor core so that the greatest radial thickness is at the point of highest fluence with lesser thicknesses at adjacent locations where the fluence level is lower. The neutron panels are disposed between the core barrel and the interior of the reactor vessel to maintain radiation exposure to the vessel within acceptable limits.

Abstract: A lower internals nuclear reactor structure having a tubular core barrel with an upper and lower open end, coaxially supported therein. A reflector having an outside curvature that substantially matches the curvature of the inside surface of the core barrel and substantially contacts the inside surface substantially over an axial length of the core, is fixedly connected to the inside surface of the core barrel at a plurality of axial and circumferential locations to be substantially supported by the inside surface of the core barrel.

Abstract: A neutron reflector bolt fastening structure is disclosed in which even upon relaxation in the fastening forces thereof being generated in tie rods for divided stage portions as a result of neutron irradiation, it is possible to press the neutron reflector firmly against a core vessel. The neutron reflector bolt fastening structure includes: a neutron reflector which includes of a plurality of divided stage portions and situated in a core vessel in a reactor vessel; a plurality of tie rods for fixing the neutron reflector to the core vessel; and a plurality of bolts for exclusively fixing the lowermost stage portion of the plurality of stage portions of the neutron reflector to the core vessel.

Abstract: A high-temperature nuclear reactor, cooled by a liquid fluoride salt, is described. The reactor uses an annular fuel pebble comprised of an inert graphite center kernel, a TRISO fuel particles region, and a graphite outer shell, with an average pebble density lower than the density of the liquid salt so the pebbles float. The pebbles are introduced into a coolant entering the reactor and are carried into the bottom of the reactor core, where they form a pebble bed inside a plurality of vertical channels inside one or more replaceable Pebble Channel Assemblies (PCAs). Pebbles are removed through defueling chutes located at the top of each PCA. Each PCA also includes channels for insertion of neutron control and shutdown elements, and channels for insertion of core flux mapping and other instrumentation.

Abstract: A nuclear reactor module includes a reactor core and a reactor housing that surrounds the reactor core about its sides, wherein the reactor housing is configured to direct coolant through the reactor core. A neutron reflector is located between the reactor core and the reactor housing, wherein the neutron reflector has a plurality of inlet ports facing the reactor core. The neutron reflector also has a plurality of outlet ports fluidly connected to the inlet ports to direct a portion of the coolant through the neutron reflector.

Abstract: A fast reactor 1 controlled with a reflector comprises: a reactor vessel 7 accommodating therein a coolant 5; a reactor core 2 disposed in the reactor vessel 7 and immersed in the coolant 5; and a reflector 4 that vertically moves for adjusting leakage of neutrons generated from the reactor core 2 to control a reactivity of the reactor core 2, the reflector 4 including a neutron reflecting part 4a disposed on an outside of the reactor core 2 in a vertically movable manner, the neutron reflecting part 4a having a neutron reflecting ability higher than that of the coolant 5, and a cavity part 4b positioned above the neutron reflecting part 4a, the cavity part 4b having a neutron reflecting ability lower than that of the coolant 5. The neutron reflecting part 4a is formed of a plurality of metal plates 37 that are stacked on each other. Each of the metal plates 37 has a plurality of coolant channels 36 through which the coolant 5 flows.

Abstract: A reflector system of a fast reactor according to the present invention comprises a reflector having a neutron reflecting portion reflecting a neutron radiated from a reactor core, and a cavity portion provided above the neutron reflecting portion and having a lower neutron reflecting capacity than a coolant, and a reflector drive apparatus coupled to the reflector and moving the reflector in a vertical direction. The reflector drive apparatus has a driving portion which is coupled to the reflector via a drive shaft, and drives the reflector up and down, and a load sensing portion which is provided between the driving portion and the drive shaft, and senses a load of the reflector. A detecting portion receiving a load signal from the load sensing portion so as to detect a breakage of the cavity portion of the reflector is connected to the load sensing portion.

Abstract: A method for fabricating a supermirror for forming a neutron guide. In the method, a neutron supermirror, which is widely used in the formation of thin films in cold neutron guides and the spectrometer field, is fabricated with nickel thin films and titanium thin films, having varying thickness, using a combination of monochromator structures in which nickel thin films and titanium thin films, having the same thickness, are stacked in the form of periodic structures. According to the method, a combination of monochromator structures having a variety of different thicknesses is formed, such that the amount of the overlap of peaks due to the monochromator structures can be adjusted to increase reflectivity, and some of the monochromator structures can be removed during the fabrication of the supermirror to make it easy to extract monochromatic beams, such that it is easy to fabricate a transmission monochromator, rather than a reflection monochromator.

Abstract: In a nuclear reactor neutron panels varying in thickness in the circumferential direction are disposed at spaced circumferential locations around the reactor core so that the greatest radial thickness is at the point of highest fluence with lesser thicknesses at adjacent locations where the fluence level is lower. The neutron panels are disposed between the core barrel and the interior of the reactor vessel to maintain radiation exposure to the vessel within acceptable limits.

Abstract: A neutron reflector bolt fastening structure is disclosed in which even upon relaxation in the fastening forces thereof being generated in tie rods for divided stage portions as a result of neutron irradiation, it is possible to press the neutron reflector firmly against a core vessel. The neutron reflector bolt fastening structure includes: a neutron reflector which includes of a plurality of divided stage portions and situated in a core vessel in a reactor vessel; a plurality of tie rods for fixing the neutron reflector to the core vessel; and a plurality of bolts for exclusively fixing the lowermost stage portion of the plurality of stage portions of the neutron reflector to the core vessel.

Abstract: This invention extends the Kirkpatrick-Baez (KB) mirror focusing geometry to allow nondispersive focusing of neutrons with a convergence on a sample much larger than is possible with existing KB optical schemes by establishing an array of at least three mirrors and focusing neutrons by appropriate multiple deflections via the array. The method may be utilized with supermirrors, multilayer mirrors, or total external reflection mirrors. Because high-energy x-rays behave like neutrons in their absorption and reflectivity rates, this method may be used with x-rays as well as neutrons.

Abstract: A tie rod having a cruciform cross section is provided with steps for fixing sheaths at tips of cruciform arms of the tie rod; the tips of each of sheaths are fitted onto the steps of the tie rod, each of the sheaths having a U-shaped cross section; and each of the sheaths is fixed to the tie rod by performing a laser welding using a YAG laser beam or a CO2 laser beam with the sheath being fitted onto the tie rod to achieve a continuous weld of at least a part of the tie rod in a longitudinal direction thereof. An axial center position of the beam is shifted from an end face position of the step of the tie rod at least toward an axis center of the tie rod.

Abstract: A neutron radiation installation for treatment of different types of cancer tumours, comprising a source of neutrons (11), like a nuclear reactor or an accelerator dependent source of radiation, a conventional filter (14) for reducing the radiation energy to a suitable level for radiation treatment of cancer tumours, having low energetic neutron beams of an energy of between 1 eV and 40 keV, or preferably between 1 keV and 20 keV, and a radiation tube (22) out of which radiation beams are emitted towards a patient (10) having a cancer tumour (23), whereby an optimum radiation is obtained at a distance of between 50 and 100 cm from the output surface of the conventional filter (14), and in which the installation comprises an additional radiation filter (21) mounted between the conventional filter (14) and the output of the radiation tube, which additional filter is of a material which filters off neutrons in the epithermic spectrum from low energetic neutron beams up to an energy of about 1 keV, in particular

Abstract: A process for the treatment of radioactive graphite which includes the following steps: (i) reacting the radioactive graphite at a temperature in the range of from 250° C. to 900° C. with superheated steam or gases containing water vapor to form hydrogen and carbon monoxide; (ii) reacting the hydrogen and carbon monoxide from step (i) to form water and carbon dioxide; and (iii) reacting the carbon dioxide of step (ii) with metal oxides to for carbonate salts. The process enables radioactive graphite, such as graphite moderator, to be treated either in-situ or externally of a decommissioned nuclear reactor.

Abstract: A neutron guide in which lengths of cylindrical glass tubing have rectangular glass plates properly dimensioned to allow insertion into the cylindrical glass tubing so that a sealed geometrically precise polygonal cross-section is formed in the cylindrical glass tubing. The neutron guide provides easier alignment between adjacent sections than do the neutron guides of the prior art.

Abstract: A source for boron neutron capture therapy (BNCT) comprises a body of photoneutron emitter that includes heavy water and is closely surrounded in heat-imparting relationship by target material; one or more electron linear accelerators for supplying electron radiation having energy of substantially 2 to 10 MeV and for impinging such radiation on the target material, whereby photoneutrons are produced and heat is absorbed from the target material by the body of photoneutron emitter. The heavy water is circulated through a cooling arrangement to remove heat. A tank, desirably cylindrical or spherical, contains the heavy water, and a desired number of the electron accelerators circumferentially surround the tank and the target material as preferably made up of thin plates of metallic tungsten.

Abstract: The invention concerns a moderator material used for moderation of high-velocity neutrons, in particular of fission neutrons, to epithermal neutrons. The principal components of the moderator material are aluminum fluoride and aluminum metal, which have been formed into a dense composite substantially free of pores, wherein the material contains 20 to 50%-vol. of aluminum metal and 80 to 50%-vol. of aluminum fluoride. Further, the use of the moderator material in accordance with the invention in neutron capture therapy of cancer tumours is described, such as in boron neutron capture therapy (BNCT).

Abstract: A pressurized water reactor ("PWR") radial reflector fabricated of 20% to 30% cold worked AISI Type 316 stainless steel blocks will experience about 0.14% volumetric swelling at a neutron dose level of about 100 dpa at retirement. The reflector will not be susceptible to swelling-embrittlement at retirement.

Abstract: A fuel assembly and a reactor core using same which are able to increase size of the fuel assembly with ensuring thermal margin and reactor shut down margin.A distance between centers of adjacent fuel assemblies is about 23 cm, which is enlarged about 1.5 times of conventional fuel assemblies. A thickness of water gap region is about 16 cm, which is relatively thinner than that of prior art. While, H/U ratio is about 5 as same as that of the prior art, and decreasing amount of non-boiling water in the water gap region is arranged in a channel box as water rods. Consequently, a ratio of transversal cross section area of the water rods to transversal cross section area of the fuel rods becomes about 0.6, and local power peaking factor can be decreased and thermal margin can be increased. Further, the transversal cross section area of the water rod is selected to be 15 cm.sup.2 so as to ensure the reactor shut down margin by reducing excess reactivity.

Abstract: A nuclear reactor reflector is disclosed that comprises a stack of reflector blocks with vertical water flow passages to cool the reflector. The interface between blocks is opposite support points for reactor fuel rods. Water flows between the reflector and the reactor barrel from passages in a bottom block. The top block contains a flange to limit this flow and the flange has a slot to receive an alignment pin that is welded to the barrel. The pin is held in the slot by two removable shims. Alignment bars extend the length of the stack in slots machined in each block when the stack is assembled.

Abstract: A fast reactor comprises a reactor vessel to be arranged vertically in a reactor building, a reactor vessel upper structure disposed on an upper portion in the reactor vessel, a drum structure suspended from the reactor vessel structure into a central portion in the reactor vessel so as to define an annular portion between an outer periphery of the drum structure and an inner periphery of the reactor vessel, and a reactor core disposed in the drum structure. A reflector is disposed in the reactor vessel and is vertically movable along an outer periphery of the reactor core. The reflector may be composed of grain materials movable by gravity. An intermediate heat exchanger is further disposed at a portion above the reactor core and an electromagnetic pump is disposed in the reactor vessel for circulating coolant. The reactivity of the reactor core can be controlled by the reflector to thereby reduce the neutron irradiation amount to the reactor vessel.

Abstract: An improved neutron reflecting supermirror structure comprising a plurality of stacked sets of bilayers of neutron reflecting materials. The improved neutron reflecting supermirror structure is adapted to provide extremely good performance at high incidence angles, i.e. up to four time the critical angle of standard neutron mirror structures. The reflection of neutrons striking the supermirror structure at a high critical angle provides enhanced neutron throughput, and hence more efficient and economical use of neutron sources.

Abstract: Water rod configurations, such as for a boiling water nuclear reactor, are provided. An efficiency parameter is defined which relate to how well-used the sacrificed fuel rod positions are. Four particular water rod configurations are described, which produce high efficiency, such as having a water rod efficiency greater than about 0.6, preferably greater than about 0.7. Desired moderation is achieved by providing for sacrifice of more than four and less than nine lattice positions. The first "peanut" configuration has a cross-section with two round-cornered triangular regions, integrally connected by a constricted portion. The second configuration has a substantially rectangular cross-section. The third "clover" configuration has a four-lobed shape. The fourth "figure 8" configuration has two substantially circular cross-sectional portions. A method for analysis and design, using a new efficiency parameter, is provided.

Abstract: The invention relates to a nuclear reactor with improved efficiency.The nuclear reactor comprises a massive partition (18) of material reflecting high energy neutrons at the circumference of the core (7) of the reactor, two layers (19 and 20) of material absorbing low energy neutrons and containing fertile material arranged one at the lower part and one at the upper part of the core (7) and an assembly of neutron energy spectrum variation rods (27). The rods (27) are associated with mechanisms permitting them to be either fully inserted into the core (7), or fully extracted. These rods (27) consist of a material absorbing low energy neutrons and permit a shift of the neutron spectrum towards the high energies.The invention is particularly applicable to pressurized water nuclear reactors.

Abstract: An improved neutron reflecting supermirror structure comprising a plurality of stacked sets of bilayers of neutron reflecting materials. The improved neutron reflecting supermirror structure is adapted to provide extremely good performance at high incidence angles, i.e. up to four time the critical angle of standard neutron mirror structures. The reflection of neutrons striking the supermirror structure at a high critical angle provides enhanced neutron throughput, and hence more efficient and economical use of neutron sources. One layer of each set of bilayers consist of titanium, and the second layer of each set of bilayers consist of an alloy of nickel with carbon interstitially present in the nickel alloy.

Abstract: A ball-bed (pebble-bed) nuclear reactor, instead of having fuel elements more or less continuously withdrawn and new or reconstituted fuel elements more or less continuously reintroduced, is initially partly filled with fuel balls of which two-thirds have a fissionable material content 12% below and the upper third 24% higher than the average content. This filling meets the requirements of criticality in order to begin operation. Thereafter, fuel balls are added slowly, a few hundred per day, having 150 to 250% of the average fissionable material content of the initial loading thus preserving the criticality requirements, while keeping the temperature within safe limits until the reactor cavern is filled. Thereafter the reactor is shut down, cooled off, pressure relieved and emptied, the last step typically from above. An ordered array of the fuel balls in regular layers avoids excess pressure loads on the reflector over the life time of the filling.

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 multi-region reactor core pebble bed high temperature gas reactor comprises a pebble bed reactor core housed within a pressure vessel and charged with spherical fuel. The reactor core is surrounded by a reflector wall comprising a partition wall which partitions the reactor core into a plurality of reactor core sub-regions. The reflector wall comprises a plurality of layers of reflector blocks, adjacent blocks of a layer being secured against one another by removable tapered keys wedged therein between.

Abstract: A reactor core for a gas-cooled reactor, which core is composed of a plurality of prismatic bodies (2) of graphite containing nuclear fuel and having a top wall, a bottom wall and a plurality of vertically extending side walls, each graphite body (2) being provided with a plurality of first coolant flow channels (4) extending vertically between the top wall and the bottom wall, and with a plurality of second coolant flow channels (6) extending transversely to the first channels (4) and each interconnecting a plurality of the first channels (4).

Abstract: A new design for nuclear reactor internals resulting in reduced fast neutron leakage to the reactor vessel. The first step of the two-stage process reflects high energy or fast neutrons back into the core, by placement of a reflector made of tungsten, stainless steel, or zirconium oxide in the baffle barrel region. The second stage involves reducing the energy of any fast neutrons that may pass through the reflector by the use of a neutron energy reducer, composed of an hydrogenous material such as titanium hydride, surrounding the core barrel in the areas of high neutron flux. In addition to protecting the reactor vessel wall and increasing the operating life of a nuclear reactor, the neutron economy in the core, and hence the operating efficiency of a nuclear power plant, are significantly increased.

Abstract: Modular neutron reflector assemblies removably insertable into the irregular space in a nuclear reactor between a generally cylindrical array of square fuel assemblies comprising the core and the cylindrical core barrel surrounding the core, include an elongated enclosure having a strongback adjacent the core barrel and flat plates adjacent the fuel assemblies. The strongback is thicker than the steel plates by an amount which results in the strongback and plates reaching approximately the same temperature to minimize thermal stresses despite the 8 to 20 times greater nuclear heating at the core side of the enclosure as opposed to that at the core barrel side. The enclosure is suspended by a single point mounting on the core barrel which permits vertical, radial, and circumferential expansion but a pin depending from the lower end of the enclosure slides in a vertical bore in the reactor lower core support plate to limit lateral movement while allowing unrestrained vertical expansion and contraction.

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 low capacity nuclear reactor with spherical fuel elements laid out in an underground configuration and characterized by a compact structure and the far-reaching elimination of active operating installations, such as a charging apparatus, gas purification installations and control systems. The reactor is particularly suitable for generation of heat for heating purposes. The graphite reflector surrounding the pile of fuel elements on all sides includes layers of spherical graphite elements with a diameter equal to that of the fuel elements. The poured part of the graphite reflector and the pile of fuel elements are located in a metal core vessel made of lattice work or perforated sheet metal and capable of supporting the entire weight of the graphite and fuel elements. The mesh or the holes of cage-like core vessel are smaller than the diameter of the spherical elements.

Abstract: A high temperature reactor having a reactor core filled with spherical fuel elements is provided comprising a graphite side reflector including at least one nose-like projection protruding radially into the reactor core from said graphite said reflector, said at least one nose-like projection including a 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, and sealing means positioned in said continuous opening and cooperatively engaged with the portion of said nose-like projections defining said vertically disposed continuous opening, said sealing means being so configured and so cooperatively engaged so as to permit gaseous communication between said cavity and said core while preventing passage of said discrete absorber material elements through said continuous passage.