Abstract: A method of operating a nuclear reactor includes operating a valve actuator to open and close a valve in fluid communication with a nuclear reactor fluid control system. The valve actuator includes a motor having windings of magnet wire. The magnet wire includes a layer of insulating material disposed over a conductor. The layer of insulating material comprises polyetheretherketone (PEEK) and has a thickness between about 0.025 mm and about 0.381 mm. A method of replacing a valve actuator motor with such a motor having windings formed of PEEK-insulated magnet wire is also disclosed. A method of coupling a valve actuator with such a motor having windings formed of PEEK-insulated magnet wire to a valve is also disclosed.

Abstract: In response to a change in a thermal operational parameter in a nuclear fission reactor, reactivity is controlled by driving a neutron absorption parameter modifying material to or from a region of the core of the nuclear fission reactor. The apparatus includes a driver material disposed in a first reservoir portion and a second reservoir portion of a first reservoir and connected by a first conduit. A high-Z material may be distributed in the driver material. The neutron absorption parameter modifying material is disposed in both a second reservoir and the second reservoir portion of the first reservoir. A portion of the neutron absorption parameter modifying material is in physical contact with a portion of the driver material in the second reservoir portion. The neutron absorption parameter modifying material is driveable by the driver material between the second reservoir portion and the second reservoir through a second conduit.

Abstract: There are provided: a container body (11) that has an opening in one end; a lid member (12A) that seals the opening; a prismatic pipe (30) that is arranged in the container body (11); a fuel holder (20) that covers a side surface of a fuel assembly when inserted into the prismatic pipe (30); and pressing members (37a, 37b) that are arranged on the prismatic pipe (30) and press the fuel holder (20), in the prismatic pipe (30), against inner surfaces of the prismatic pipe (30). One end (23) of the fuel holder (20) is formed in a tapered shape inclining toward an inside of the fuel holder (20). One end of the prismatic pipe (30) is provided with a first guide member (40) that has a recess (41) conforming to a shape of the one end (23) of the fuel holder (20).

Abstract: A reactor core is immersed in a liquid metal coolant in a core barrel of a liquid metal cooled reactor. The reactor core includes a plurality of fuel assemblies contained in the core barrel, a neutron absorber that absorbs a neutron in the reactor core, and a neutron moderator that moderates a neutron therein so as to control a reactivity of the reactor core. The neutron absorber and the neutron moderator constitute a mixture contained in reactivity control assemblies of the reactor core in the liquid metal coolant prior to immersion of the reactor core. The neutron moderator is composed of zirconium hydride.

Abstract: A method for controlling a nuclear reactor is disclosed. The method includes providing a moderator zone in a core of the nuclear reactor, providing a fuel in the moderator zone, and providing one or more housings, each having a cavity, adjacent to the fuel. The method also includes allowing movement of a moderator between the moderator zone and the cavity of the one or more housings at a lower portion of the one or more housings. The method further includes confining moderator in the cavity of the one or more housings at an upper portion of the one or more housings.

Abstract: Porous nuclear fuel elements for use in advanced high temperature gas-cooled nuclear reactors (HTGR's), and to processes for fabricating them. Advanced uranium bi-carbide, uranium tri-carbide and uranium carbonitride nuclear fuels can be used. These fuels have high melting temperatures, high thermal conductivity, and high resistance to erosion by hot hydrogen gas. Tri-carbide fuels, such as (U,Zr,Nb)C, can be fabricated using chemical vapor infiltration (CVI) to simultaneously deposit each of the three separate carbides, e.g., UC, ZrC, and NbC in a single CVI step. By using CVI, the nuclear fuel may be deposited inside of a highly porous skeletal structure made of, for example, reticulated vitreous carbon foam.

Abstract: A fast reactor having a reflector control system is provided which decreases the change in reactivity of the reactor core with time without performing control of a reflector lifting speed and that of a water flow rate. The above fast reactor has a liquid metal coolant, a reactor core immersed therein, and a neutron reflector which is provided outside the reactor core and which is moved in a vertical direction for adjusting leakage of neutrons therefrom for controlling the reactivity of the reactor core. The neutron reflector described above is gradually moved in an upward direction with the change in reactivity caused by fuel burn-up, and at least a part of a lower region of the neutron reflector is a high reflection region having a high neutron reflection ability as compared to that of the other region. The high reflection region is located from the bottom to a place between one fourth and one half of the height of the neutron reflector from the bottom end thereof.

Abstract: Porous nuclear fuel elements for use in advanced high temperature gas-cooled nuclear reactors (HTGR's), and to processes for fabricating them. Advanced uranium bi-carbide, uranium tri-carbide and uranium carbonitride nuclear fuels can be used. These fuels have high melting temperatures, high thermal conductivity, and high resistance to erosion by hot hydrogen gas. Tri-carbide fuels, such as (U,Zr,Nb)C, can be fabricated using chemical vapor infiltration (CVI) to simultaneously deposit each of the three separate carbides, e.g., UC, ZrC, and NbC in a single CVI step. By using CVI, the nuclear fuel may be deposited inside of a highly porous skeletal structure made of, for example, reticulated vitreous carbon foam.

Abstract: A fast reactor having a reflector control system is provided which decreases the change in reactivity of the reactor core with time without controlling a reflector lifting speed and a water flow rate. The fast reactor has a neutron reflector provided outside the reactor core and which is moved in a vertical direction for adjusting neutron leakage to control the reactivity of the reactor core. The neutron reflector is moved in an upward direction with the change in reactivity caused by fuel burn-up. At least a part of a lower region of the neutron reflector may be a region having a high neutron reflection ability as compared to that of the other region. The high reflection region is located at the bottom of the neutron reflector and extends from between one fourth and one half of the height of the neutron reflector.

Abstract: In a nuclear reactor in which a primary coolant is contained, the primary coolant moves upwardly from the core by an operation thereof. An annular steam generator is arranged in an upper side of the core into which the upwardly moving primary coolant flows and transfers heat in the primary coolant into water therein to generate a steam. A passage structure defines a coolant passage for the primary coolant to an outside of the core. The heat-transferred primary coolant in the annular steam generator flows downwardly in the coolant passage so as to flow into the core, thereby moving upwardly. A reactor vessel is arranged to surround the coolant passage so as to contain the core, the annular steam generator and the passage means therein.

Abstract: In a nuclear reactor in which a primary coolant is contained, the primary coolant moves upwardly from the core by an operation thereof. An annular steam generator is arranged in an upper side of the core into which the upwardly moving primary coolant flows and transfers heat in the primary coolant into water therein to generate a steam. A passage structure defines a coolant passage for the primary coolant to an outside of the core. The heat-transferred primary coolant in the annular steam generator flows downwardly in the coolant passage so as to flow into the core, thereby moving upwardly. A reactor vessel is arranged to surround the coolant passage so as to contain the core, the annular steam generator and the passage means therein.

Abstract: A reactivity control rod adapted to be used in a reactor core of a fast reactor and disposed at a substantially central portion of the reactor core for controlling a reactivity therein. The reactivity control rod includes a wrapper tube surrounded by a plurality of fuel rods in a reactor core, and a plurality of neutron absorber rods arranged in the wrapper tube. At least one of the plurality of neutron absorber rods includes a cladding tube and a mixture filled in the cladding tube. The mixture is composed of a neutron absorber that absorbs a neutron and a neutron moderator that moderates the neutron.

Abstract: A device comprising a bundle of channels (8, 23), tubes or similar units permanently is arranged in the reactor and designed to contain a neutrophage fluid that absorbs neutrons.

Abstract: The present invention is used to reduce thermal load itself, being the cause to generate stress, which develops near liquid surface in a nuclear reactor wall and to contribute to further improvement of safety. A partition member (5) is arranged above a coolant liquid surface (9) in an annulus space (3) between a reactor vessel (1) and a guard vessel (2), a low-temperature gas is circulated through the annulus space above the partition member to cool down, the gas is circulated through the annulus space from under the coolant liquid surface to the partition member, and the high-temperature gas heated under the coolant liquid surface is used to raise the temperature above the coolant liquid surface.

Abstract: A supercritical pressure water cooled reactor comprising: a reactor vessel including: a shell part for containing sub-critical pressure coolant, and an end part for containing supercritical-pressure coolant which is separated from the sub-critical pressure coolant in the reactor vessel. A core-support plate with through-holes, the core-support plate disposed-in and fixed to the reactor vessel so that the core-support plate divides space inside the reactor vessel into a supercritical-pressure portion and a sub-critical pressure portion. Fuel tubes with both open ends fixed to the through-holes, the open ends being communicated to the supercritical-pressure portion, outside of the fuel tubes being disposed in the sub-critical pressure portion; and nuclear fuel assemblies disposed in the fuel tubes.

Abstract: A fuel assembly is provided with a coolant ascending path for making coolant rise and a water rod having a coolant descending path for conducting the coolant.A ratio of a flow area in a coolant inlet port of the smallest in coolant ascending path 13 on the downstream side than large diameter tube portion 3E to a flow area of the largest in the axial direction of coolant ascending path 13 in large diameter tube portion 3E is set to be 0.2-20%.In the normal operation, the declination degree from the liquid level in the coolant ascending path, corresponding to the coolant flow rate of the liquid level formed in the coolant ascending path can be controlled. Further, at the time of the excess the change speed of the liquid level can also be controlled.

Abstract: A spectral shift-producing subassembly is composed of a plurality of sealed empty water displacement rodlets incorporating a spectral shift-producing capability. Each of the rodlets includes an elongated tube sealed at its opposite ends and having an axially-extending annular wall section of reduced thickness compared to the thickness of the wall of the remainder of the rodlet. The respective reduced thicknesses of the axial wall sections of the rodlets can be varied to adapt the rodlets to rupture at different times and permit water to enter the rodlets to produce an increase in the water/fuel ratio and thereby an increase in reactivity. The rodlets can also have different levels of pressurization to initiate rupture at different times.

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: Internal equipments suitable for use in a nuclear reactor comprise a lower plate provided with openings for the coolant leaving the core, an upper plate, support columns connecting the plates together and guides for the vertically movable control clusters. Each guide has an upper section fixed to the upper plate and a lower section extending between the upper and lower plates. The lower section (32) comprises a base bearing on a frusto-conical seat fast with the lower plate and is subjected to the action of resilient means exerting a force pressing the base on the seat.

Abstract: An apparatus for achieving increased fuel efficiency in a nuclear reactor wherein spectral shift is utilized to adjust for excess reactivity. This feature is achieved by stationary displacer rods within the fluid moderator of the reactor, with these stationary displacer rods decreasing ineffective volume during operation of the reactor whereby the effective volume of the fluid moderator increases as the nuclear fuel is burned. This decrease in effective volume is achieved by providing a sacrificial material in the displacer rods that is dissolved (or volatilized, etc.) by the fluid moderator. The composition of the sacrificial material can be varied along the length of the rod so as to achieve the desired reduction of volume despite a temperature gradient along the rod.

Abstract: A method and apparatus for achieving increased fuel efficiency in a nuclear reactor wherein spectral shift is utilized to adjust for excess reactivity. This feature is achieved by stationary displacer rods within the fluid moderator of the reactor, with these stationary displacer rods decreasing in effective volume during operation of the reactor whereby the effective volume of the fluid moderator increases as the nuclear fuel is burned. This decrease in effective volume is achieved by providing a sacrificial material in the displacer rods that is dissolved (or volatilized, etc.) by the fluid moderator. The compositon of the sacrificial material can be varied along the length of the rod so as to achieve the desired reduction of volume despite a temperature gradient along the rod.

Abstract: A fuel assembly has a water rod which consists of a coolant ascending path and a coolant descending path, the coolant ascending path opening below a fuel support of a lower tie plate, the coolant descending path opening above the fuel support and adapted to guide downwardly the coolant that has flowed up the coolant ascending path to the upper portion of the water rod. The lateral cross section of the coolant ascending path is more than 25 times that of the coolant descending path.The nuclear reactor with these fuel assemblies loaded in the core is operated as follows. After startup of the reactor when the reactor power is low, all the control rods inserted in the core are withdrawn completely. Then, the reactor power is controlled by regulating a liquid level formed in the water rods. This reactor operation method prolongs the lifetime of the control rods, thereby reducing the number of times they have to be replaced.

Abstract: A control element for reactivity control of a fission source provides an atomic density of .sup.3 He in a control volume which is effective to control criticality as the .sup.3 He is spin-polarized. Spin-polarization of the .sup.3 He affects the cross section of the control volume for fission neturons and hence, the reactivity. An irradiation source is directed within the .sup.3 He for spin-polarizing the .sup.3 He. An alkali-metal vapor may be included with the .sup.3 He where a laser spin-polarizes the alkali-metal atoms which in turn, spin-couple with .sup.3 He to spin-polarize the .sup.3 He atoms.

Abstract: A fuel assembly in a nuclear reactor has a spectral shift apparatus including a plurality of displacer rods for controlling reactivity in the assembly and an apparatus for refurbishing the displacer rods for reuse. Each displacer rod contains a quantity of water equivalent to a small fraction of the rod volume. Also, the spectral shift apparatus includes a manifold with a central plenum and a rupturable disk connected to the manifold. The manifold is connected in flow communication with the displacer rods. The disk which seals the displacer rods as well as the manifold plenum is rupturable at a given pressure differential thereacross so as to allow entry of the moderator/coolant liquid into the manifold and rods. Also, a screen adjacent the disk restricts it to rupturing in one direction only.

Abstract: A fuel assembly for a pressurized water nuclear reactor incorporating fluid moderator spectral shift control means. During the first part of the fuel cycle when there is excess reactivity, neutron moderation may be decreased by replacing a portion of the water within the core with a less effective moderator such as heavy water. During the life of the fuel, the heavy water is gradually replaced with regular water. The fuel assembly incorporates the necessary means and apparatus to effectuate such control.

Abstract: A method and apparatus for extending the life of a core of a water moderated nuclear reactor by spectral shift comprising the displacement of a portion of the moderator in the core by a gas having a low neutron cross-section during the initial stage of the life of the core and displacing the gas and replacing it with moderator during the latter part of the life of the core.

Abstract: A fuel assembly in a nuclear reactor has a spectral shift apparatus including a plurality of displacer rods for controlling reactivity in the assembly and an apparatus for refurbishing the displacer rods for reuse. Each displacer rod contains a quantity of water equivalent to a small fraction of the rod volume. Also, the spectral shift apparatus includes a manifold with a central plenum and a rupturable disk connected to the manifold. The manifold is connected in flow communication with the displacer rods. The disk which seals the displacer rods as well as the manifold plenum is rupturable at a given pressure differential thereacross so as to allow entry of the moderator/coolant liquid into the manifold and rods. Also, a screen adjacent the disk restricts it to rupturing in one direction only.

Abstract: Apparatus is disclosed for introducing a low neutron moderating fluid into the reactor vessel of a spectral shift pressurized water nuclear reactor and for distributing the moderating fluid through the lower core support plate into the fuel assemblies in the core.

Abstract: A moderator control apparatus is provided for use with a fuel assembly to improve fuel utilization in thereby reducing fuel cycle costs. The apparatus includes a plurality of displacer rods filled with a burnable poison gas which are inserted into the guide thimbles of the fuel assembly to displace a portion of the coolant in thus reducing the H/U ratio at the start of the cycle. The displacer rods are connected at their upper ends to a manifold which has a central opening with a plurality of inlet ports disposed about the central opening and in fluid flow communication with the rods. A rotatable valve is disposed in the central opening and operable to selectively open and close the inlet ports so as to either permit or obstruct the flow of coolant into the displacer rods in a predetermined controlled manner.

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: A nuclear reactor system in which the neutron-energy spectrum is displaced towards lower energy (enthalpy) by a control selectively operable by commands outside of the reactor. The core of the reactor contains, in addition to fuel assemblies, sealed tubes filled with helium. The selective control of the neutron energy spectrum includes a master cylinder having a master piston. The master cylinder is immersed in the coolant and admits the coolant through a check valve. The admitted coolant serves as hydraulic fluid of the cylinder. When the external command to shift the neutron-energy spectrum is entered, the master piston compresses the coolant in the master cylinder. The compressed coolant flows into slave cylinders displacing their slave pistons. The slave pistons carry piston rods which drive rupturing tools into engagement with the tubes rupturing the tubes and admitting the coolant which is a neutron moderator and enhances the moderaton of the neutron energy.

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: An arrangement for controlling the moderation of a nuclear reactor which includes multiple fuel assemblies each of which includes top and bottom nozzles with fuel rods and control rod guide thimbles located therebetween. Certain ones of said assemblies include at least one tube initially filled with a gas. One end of the tube rests on the lower nozzle upper surface while the upper end terminates at a point just below the lower plate in the upper nozzle. A spike immovably fixed in the lower plate of the upper nozzle is directed downwardly toward the end of the tube. As the tube expands or grows during operation in a reactor, and at a point where the criticality factor may proceed to less than one, the expanded tube will be pierced by the spike and thus permit the escape of gas from the tube which is then replaced by water coolant circulating through the reactor.

Abstract: A fast nuclear reactor is described which comprises a conical reactor core surrounding an embedded array of heat pipes of, per se, novel structure, carrying either moderator or nuclear fuel material as part of their working fluid. This reactor system is self-regulating, because an excessive increase in reactivity drives the fuel or moderator working fluid out of the conical core region, thereby reducing reactivity. The heat pipes are protected against burnout by a novel heat pipe envelope shape and internal wicking structure designed to increase the working fluid circulation speed with increasing heat transfer loads.

Abstract: An arrangement for controlling the moderation of a nuclear reactor which includes multiple fuel assemblies each of which includes top and bottom nozzles with fuel rods and control rod guide thimbles located therebetween. Certain ones of said assemblies include at least one tube initially filled with a gas. One end of the tube rests on the lower nozzle upper surface while the upper end terminates at a point just below the lower plate in the upper nozzle. A spike immovably fixed in the lower plate of the upper nozzle is directed downwardly toward the end of the tube. As the tube expands or grows during operation in a reactor, and at a point where the criticality factor may proceed to less than one, the expanded tube will be pierced by the spike and thus permit the escape of gas from the tube which is then replaced by water coolant circulating through the reactor.