Abstract: A system for use in shutting down a nuclear reactor includes a housing that defines a region therein sealed from an ambient environment and a gate member disposed within the region in a manner such that the gate member segregates the region into a first compartment and a second compartment isolated from the first compartment. The gate member is formed from a material having a predetermined melting point. The system further includes a neutron absorbing material disposed within the first compartment and a dispersion mechanism disposed within the region. The dispersion mechanism structured to encourage the neutron absorbing material from the first compartment into the second compartment.

Abstract: A laser wake-field acceleration (LWFA)-based nuclear fission system and related techniques are disclosed. In accordance with some embodiments, the disclosed system may be configured to accelerate charged particles, such as protons, to velocities close to the speed of light utilizing LWFA. The system also may be configured, in accordance with some embodiments, to use these high-energy relativistic charged particles in causing nuclear fission of a given downstream fissionable target, thereby releasing large amounts of harvestable energy. Optionally, the system further may be configured, in accordance with some embodiments, to utilize charged particles resulting from the fission in producing electrical energy.

Abstract: A neutron detector including a plurality of layers of converter material and a plurality of layers of detector material. Each layer of converter material can be immediately adjacent to at least one layer of detector material and each layer of detector material can be immediately adjacent to at least one layer of converter material. The neutron detector may further include a read out integrated circuit (ROIC) that is electrically coupled to the plurality of layers of detector material. A value output by the ROIC may be indicative of a neutron interacting with a layer of converter material from amongst the plurality of layers of converter material.

Abstract: A method is described for forming duplex layers including an interlayer and a corrosion resistant boundary layer on a nuclear fuel rod cladding tube for use in a water cooled nuclear reactor. The method includes forming, by thermal deposition or physical vapor deposition, on the exterior of a substrate, an inner interlayer with Mo, Ta, W or Nb or other particles, and forming, by thermal deposition or physical vapor deposition, on the interlayer, an outer corrosion resistant layer with particles selected from the group consisting of Cr, a Cr alloy, and combinations thereof. The interlayer prevents eutectic formation between the corrosion resistant layer and the substrate.

Abstract: The present invention relates to a nuclear reactor, more precisely a passive safety device applicable to a thermal neutron reactor and a nuclear fuel assembly equipped with the same. The nuclear fuel assembly for a thermal neutron reactor of the present invention includes multiple fuel rods; multiple guide thimbles arranged between the fuel rods; and a passive safety device including neutron absorber parts which are inserted in one or more guide thimbles.

Abstract: A method for guaranteeing fast reactor core subcriticality under conditions of uncertainty involves, after assembling the reactor core, conducting physical measurements of reactor core subcriticality and comparing the obtained characteristics with design values; then, if there is a discrepancy between the values of the obtained characteristics and the design values, installing adjustable reactivity rods in the reactor at the level of a fuel portion of the reactor core, wherein the level of boron-B10 isotope enrichment of the adjustable reactivity rods is selected to be higher than the level of boron-B10 isotope enrichment of compensating rods of the reactor core. The technical result consists in improving the operating conditions of absorbing elements of a compensating group of rods, eliminating the need for increasing the movement thereof, simplifying monitoring technologies used during production, and simplifying the algorithm for safe reactor control.

Abstract: An accumulator pressure monitoring system for monitoring pressure in a hydraulic circuit. The accumulator includes a first chamber filled with a gas, a second chamber filled with a liquid and a movable separator disposed between the first and second chambers. A pressure sensor measures the pressure in the first chamber; and a control unit receives pressure readings from the pressure sensor and compares the pressure readings to threshold pressure values and may control the accumulator based upon this comparison.

Abstract: An emergency spent nuclear fuel pool cooling system that requires no external electrical power source and relies on the expansion of a cryogenic fluid through an evaporator/heat exchanger submerged within the spent fuel pool, to power various components used to cool the spent fuel pool and adjacent areas and provide makeup water to the spent fuel pool. Other than the evaporator/heat exchanger to which the cryogenic fluid is connected, the remaining components employed to cool the pool and the surrounding area and provide makeup water can be contained in a relatively small, readily transportable skid.

Abstract: A heating system for a thermal electric power station water circuit includes an extraction system for extracting water from a condenser and a first set of heaters including a first water inlet fed with a first fraction of a flow coming from the extraction system, and a input for heating the extracted water. A second set of heaters includes a heater arranged in series with the extracted-water inlet of the first set, and a steam input for heating the extracted water. A condensate cooler includes a first water inlet fed by a condensate outlet of the second set of heaters, a second water inlet fed with a complementary fraction of the extracted-water flow, a first outlet for cooled condensate to be reinjected into the condenser, and a second outlet for heated water so that water leaving the first set of heaters is mixable with water from the second outlet.

Abstract: The invention relates to a steam turbine governing system for maintaining synchronization between an electrical grid and an electric generator, driven by a steam turbine, after the occurrence of a grid short circuit at the electrical grid. The governing system includes a governor adapted to control an arrangement of valves for regulating the steam flow in the steam turbine and means for measuring the voltage drop at the output of the electric generator. The governing system further includes means for measuring the electric power drop at the output of the electric generator. The governor is adapted to initiate operation of the arrangement of valves of the steam turbine in response to a voltage drop exceeding a predetermined value and to an electric power drop exceeding a predetermined value.

Abstract: A lightly hydrided/deuterated metallic plutonium-thorium fuel for use in a fast fission pool-type nuclear reactor cooled with liquid metal coolants, including lithium-7 lead eutectic, lead bismuth eutectic or lead. When so used, plutonium-239 is consumed, and merchantable heat is produced along with fissile uranium-233, which can be denatured with uranium-238 and used in light water reactors as fuel.

Abstract: Disclosed is a control rod drive mechanism. More specifically, the control rod drive mechanism includes a guide member 100 disposed in a nuclear reactor to receiving a drive shaft 2; a latch assembly 200 disposed in the guide member 100 to enable the drive shaft 2 to be withdrawn and inserted; a supporting member 300 connected to the guide member 100 to cover the drive shaft 2 and to support the latch assembly 200; and a plurality of coil housings 400 spaced apart and connected to the guide member 100 to cover the latch assembly 200, and each having a coil 410 built therein.

Abstract: An upper hole 37A and a lower hole 37B are provided at two positions, namely, upper and lower portions, of a side surface of a guide tube 27, and a thimble tube 22 is pressed against an inner circumferential surface of the guide tube 27, by a differential pressure between coolant inside and outside the upper hole 37A and the lower hole 37B.

Abstract: A control rod drive mechanism (CRDM) includes a lifting rod supporting a control rod and a holding mechanism comprising an electromagnetic circuit with magnetic poles drawn together when the electromagnetic circuit is energized to hold the lifting rod. The hold is released upon de-energizing the electromagnetic circuit. A translation mechanism linearly translates the lifting rod held by the holding mechanism. The holding mechanism may include a non-magnetic spacer between the magnetic poles that defines a gap between the drawn together magnetic poles. The translation mechanism may include latches configured to engage an upper end of the lifting rod, and the holding mechanism draws the magnetic poles together to hold the latches engaged with the upper end of the lifting rod. A four-bar cam assembly may be used to cam the latches closed in response to a vertical actuation force applied to the cam bars.

Abstract: A control rod drive mechanism (CRDM) configured to latch onto the lifting rod of a control rod assembly and including separate latch engagement and latch holding mechanisms. A CRDM configured to latch onto the lifting rod of a control rod assembly and including a four-bar linkage closing the latch, wherein the four-bar linkage biases the latch closed under force of gravity.

Abstract: An integrated reactor missile shield and crane assembly (IRMSCA) is disclosed and claimed. The IRMSCA replaces the existing concrete missile shields and reactor services crane. The IRMSCA is moveable such that the missile shield can be moved away from the reactor head, allowing the integral crane to lift the control rod drive mechanism components and other routine loads at the refueling cavity.

Abstract: Disclosed embodiments include electromagnetic flow regulators for regulating flow of an electrically conductive fluid, systems for regulating flow of an electrically conductive fluid, methods of regulating flow of an electrically conductive fluid, nuclear fission reactors, systems for regulating flow of an electrically conductive reactor coolant, and methods of regulating flow of an electrically conductive reactor coolant in a nuclear fission reactor.

Abstract: A pressurized water reactor (PWR) comprises a pressure vessel containing primary coolant water. A nuclear reactor core is disposed in the pressure vessel and includes a plurality of fuel assemblies. Each fuel assembly includes a plurality of fuel rods containing a fissile material. A control system includes a plurality of control rod assemblies (CRA's). Each CRA is guided by a corresponding CRA guide structure. A support element is disposed above the CRA guide structures and supports the CRA guide structures. The pressure vessel may be cylindrical, and the support element may comprise a support plate having a circular periphery supported by the cylindrical pressure vessel. The CRA guide structures suitably hang downward from the support plate. The lower end of each CRA guide structure may include alignment features that engage corresponding alignment features of the upper end of the corresponding fuel assembly.

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 control strategy for a pressurized water nuclear reactor that employs separate, independent control rod banks for respectively controlling Tavg and axial offset within corresponding deadbands. The strategy does not permit the control banks controlling reactor core power and the control banks controlling axial offset to move together, but normally gives preference to the control banks controlling the Tavg except when a demand signal is received simultaneously by both independent control rod banks to move in a same direction, in which case, the control bank compensating for the axial offset is given preference.

Abstract: The present invention relates to tubular elements, such as fuel assembly tubes, which are designed to be used in high pressure and high temperature water in nuclear reactors, such as pressurized water nuclear reactors. In particular, the present invention relates to a method of improving wear resistance and corrosion resistance by depositing a protective coating having a depth of from about 5 to about 25 ?m on the surface of the tubular elements. The coating is provided by nitriding the tubular element at a temperature of from about 400° C. to about 440° C. The nitridation of the tubular element can be carried out for a duration of from about 12 hours to about 40 hours.

Abstract: A digital rod control system that employs separate power modules to energize the respective coils of a magnetic jack control rod drive rod drive system so that two, independently powered grippers can simultaneously support the control rod drive rod when it is not in motion to avoid dropped rods. The basic building block of the system is two or more selecting cabinets which receive multiplex power from at least one moving cabinet and are under the control of a single logic cabinet. Each of the cabinets include monitoring features to confirm the reliability of the system.

Abstract: The invention relates to a method for regulation of operational parameters of the core of a pressurised water nuclear reactor comprising: a step of acquisition of values (FH, FB, TBC, TBF, Q) which are representative of the conditions of operating of the core of the reactor; a step of evaluation of the actual values (Tmoye, AOe, {circumflex over (P)} maxe) of the operational parameters at least according to the values acquired (FH, FB, TBC, TBF, Q); a step of selection of a control law for the concentration of a neutron-absorbent component ([B]) and for the positions of insertion (Z1 to Z5) of the groups (P1 to P5) of rods selected from at least the first and second control laws which are different from one another; and a step of regulation of the operational parameters by means of the control law selected, according to set points (Tmoyc, AOc, {circumflex over (P)} maxc) relative to the said parameters and to the actual values (Tmoye, AOe, {circumflex over (P)} maxe) evaluated.

Abstract: A securing device for a control rod in a nuclear plant contains a control rod drive and a drive housing, which encloses the control rod drive and which is configured to be fed through a reactor pressure wall. The aim of the securing device is to prevent, in the most reliable manner possible, the control rod from being extended in an uncontrolled manner. Furthermore, the securing device should be as inexpensive as possible and should pose the slightest obstacle possible to installation work. For this purpose, the drive housing has at least one coupling element for forming a force-locked and/or form-fit connection of the drive housing to the reactor pressure wall.

Abstract: A suspended basket includes a plurality of plates, tie rods, and adjustable length threaded tie rod couplings connecting threaded ends of the tie rods with threaded features of the plates. Control rod drive mechanisms (CRDMs) with CRDM motors are mounted in the suspended basket, which is suspended in a pressure vessel above a nuclear reactor core to control insertion of control rods into the reactor core. In one embodiment each adjustable length threaded tie rod coupling is a turnbuckle coupling that includes a sleeve threaded onto the threaded end of the tie rod and onto the threaded feature of the plate, and the sleeve is rotatable to adjust the position of the tie rod respective to the plate. Guide frames may be mounted in the suspended basket between the CRDMs and the nuclear reactor core to guide portions of the control rods withdrawn from the nuclear reactor core.

Abstract: A control rod drive mechanism according to the present invention includes a cylindrical guide tube having a latch hole, a hollow piston coupled to the control rod and freely moving up and down within the guide tube, a latch provided in the hollow piston so as to freely swing and freely engaging with and disengaging from the latch hole of the guide tube, and a spring locking the latch to the latch hole of the guide tube. Further, an elevating member having a latch guide which can come into contact with the latch is provided so as to freely move up and down within the guide tube. Further, the latch includes a guide surface coming into contact with the latch guide of the elevating member, and the latch guide includes a guide roller coming into contact with the guide surface of the latch.

Abstract: A tertiary shutdown system for a liquid metal reactor that eliminates the need for considering an ATWS in setting the thermal power limits of the reactor. The shutdown system includes a reservoir of neutron absorber material that is sealed by a valve that may actively dispense the absorber upon operator command, into a stagnant pool of sodium in the core that is confined to prevent the absorber material from entering the coolant flowing through the core. Additionally, the valve may be passively open to release the absorber material into the stagnant pool of sodium when the temperature at the valve exceeds a predetermined limit.

Abstract: A nuclear reactor includes a pressure vessel, and a control rod assembly (CRA) including at least one movable control rod, a control rod drive mechanism (CRDM) for controlling movement of the at least one control rod, and a coupling operatively connecting the at least one control rod and the CRDM. The coupling includes a connecting rod engaged with the CRDM and a terminal element connected with a lower end of the connecting rod and further connected with the at least one control rod. In some embodiments the terminal element includes a first portion comprising a first material having a first density and a second portion comprising a second material having a second density that is greater than the first density. In some embodiments the terminal element has a largest dimension parallel with the connecting rod that is greater than or equal to a largest dimension transverse to the connecting rod.

Abstract: The present invention relates to a control rod drive mechanism assembly for a nuclear reactor having a nuclear reactor vessel, a nuclear reactor core, a reactor vessel head, a latch housing nozzle, a latch housing, a rod travel housing, a latch assembly, a drive rod assembly and a rod control cluster assembly. The latch housing is integrated with the latch housing nozzle, the rod travel housing is welded to the latch housing, and the latch assembly is connected to the rod travel housing. The latch assembly includes the drive rod assembly and the rod control cluster assembly which is attached to the drive rod assembly.

Abstract: A standoff supporting a control rod drive mechanism (CRDM) in a nuclear reactor is connected to a distribution plate which provides electrical power and hydraulics. The standoff has connectors that require no action to effectuate the electrical connection to the distribution plate other than placement of the standoff onto the distribution plate. This facilitates replacement of the CRDM. In addition to the connectors, the standoff has alignment features to ensure the CRDM is connected in the correct orientation. After placement, the standoff may be secured to the distribution plate by bolts or other fasteners. The distribution plate may be a single plate that contains the electrical and hydraulic lines and also is strong enough to provide support to the CRDMs or may comprise a stack of two or more plates.

Abstract: Illustrative apparatuses, assemblies, and methods for controlling reactivity in a nuclear fission reactor are disclosed, illustrative nuclear fission reactors are disclosed, and illustrative methods for fabricating a reactivity control apparatus are disclosed.

Abstract: A method of operating a nuclear reactor is disclosed. The reactor (1) encloses a core having a plurality of fuel rods (9). Each fuel rod (9) includes a cladding and fuel pellets of a nuclear fuel. The fuel pellets are arranged in an inner space of the cladding leaving a free volume comprising an upper plenum, a lower plenum and a pellet-cladding gap. The reactor is operated at a normal power and a normal inlet sub-cooling during a normal state. The reactor is monitored for detecting a defect on the cladding of any of the fuel rods. The operation of the reactor is changed to a particular state after detecting such a defect. The particular state permits an increase of the free volume in the defect fuel rod. The reactor is operated at the particular state during a limited time period, after which the reactor is operated at the normal state.

Abstract: A method for treating neutrons generated from spent nuclear fuel is provided, which includes a step of injecting neutron absorption material into the spent nuclear fuel storage water in which cooling function is lost. Accordingly, as the neutron absorption material in the form of particles is injected into a spent nuclear storage pool missing cooling function and deposited on the surface of the spent nuclear fuel, the possibility reaching nuclear criticality is reduced since the neutrons generated from spent nuclear fuel are absorbed. Also, immediate neutron absorbing power is provided upon refilling the pool water into the spent nuclear fuel storage pool in which pool water is depleted.

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: In an initial core of a nuclear reactor, a plurality of water regions having a square cross section for occupying a cross sectional area capable of disposing four fuel assemblies are formed. No fuel assemblies are loaded in these water regions. In the initial core, each fuel assembly is supported by fuel supports. A pressure loss of a first orifice installed in a cooling water supply passage formed in first fuel supports disposed in a central portion of the initial core is larger than that of a second orifice installed in a cooling water supply passage formed in second fuel supports disposed in a peripheral portion surrounding the central portion. Each water region is formed right above a part of the first fuel supports disposed in the central portion. The control rod operation in the nuclear reactor can be simplified by action of cooling water in the water regions.

Abstract: A fast reactor having a reactivity control reflector has a reactor vessel in which a coolant is accommodated, a reactor core which is installed in the reactor vessel and dipped with the coolant, and a reflector installed outside of the reactor core so as to be movable in a vertical direction for controlling the reactivity of the reactor core. The reflector of the fast reactor has a lower neutron reflecting portion having a neutron reflection capability higher than that of the coolant and an upper cavity portion located above the neutron reflecting portion and having a neutron reflection capability lower than that of the coolant. The cavity portion is composed of a plurality of cylindrical hermetically-sealed vessels.

Abstract: The present invention relates to a method for detecting the drop of a cluster in a pressurized-water nuclear reactor, comprising the steps of: detecting a negative time derivative of the neutron flux, and comparing the absolute value of said time derivative to a first threshold value (S1); triggering a time delay (?T) if said absolute value is greater than said threshold value (S1); detecting a positive time derivative of said neutron flux, and comparing the absolute value of said time-derivative to a second threshold value (S2); and triggering the emergency shutdown of the reactor if the absolute value of said positive time derivative of said flux becomes greater than said second threshold value (S2) during said time delay (?T).

Abstract: A rector shutdown system includes a reactor, a control-rod drive unit that can drive a control rod in pulling and inserting directions with respect to a fuel assembly, a power source that can supply power to the control-rod drive unit, and a power converter that is provided between the control-rod drive unit and the power source, in which when power supply is cut off, the control-rod drive unit inserts the control rod into the fuel assembly to stop nuclear reaction in the reactor, and the rector shutdown system includes a reactor trip breaker provided between the power converter and the control-rod drive unit, a safety protection-system device that controls the reactor trip breaker to cut off power supply to the control-rod drive unit, and a CCF device that controls the power converter to cut off power supply to the control-rod drive unit.

Abstract: A control rod guide frame comprises a self supporting stack of two or more columnar elements defining a central passage. The columnar elements may include mating features that mate at abutments between adjacent columnar elements of the stack. The control rod guide frame is suitably used in conjunction with a control rod drive mechanism (CRDM) operatively connected with at least one control rod, and a nuclear reactor core, in which the CRDM moves the at least one control rod into and out of the nuclear reactor core under guidance of the control rod guide frame. In another embodiment, a control rod guide frame comprises a stack of two or more columnar elements defining a central passage having a constant cross-section as a function of position along the central passage. In another embodiment, a control rod guide frame comprises an extruded columnar element providing continuous control rod guidance.

Abstract: A nuclear reactor includes a pressure vessel, and a control rod assembly (CRA) including at least one movable control rod, a control rod drive mechanism (CRDM) for controlling movement of the at least one control rod, and a coupling operatively connecting the at least one control rod and the CRDM. The coupling includes a connecting rod engaged with the CRDM and a terminal element connected with a lower end of the connecting rod and further connected with the at least one control rod. In some embodiments the terminal element includes a first portion comprising a first material having a first density and a second portion comprising a second material having a second density that is greater than the first density. In some embodiments the terminal element has a largest dimension parallel with the connecting rod that is greater than or equal to a largest dimension transverse to the connecting rod.

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: A control rod drive mechanism (CRDM) comprises a lead screw, a motor threadedly coupled with the lead screw to linearly drive the lead screw in an insertion direction or an opposite withdrawal direction, a latch assembly secured with the lead screw and configured to (i) latch to a connecting rod and to (ii) unlatch from the connecting rod, the connecting rod being free to move in the insertion direction when unlatched, and a release mechanism configured to selectively unlatch the latch assembly from the connecting rod.

Abstract: Disclosed embodiments include nuclear fission reactor cores, nuclear fission reactors, methods of operating a nuclear fission reactor, and methods of managing excess reactivity in a nuclear fission reactor.

Abstract: Disclosed embodiments include nuclear fission reactor cores, nuclear fission reactors, methods of operating a nuclear fission reactor, and methods of managing excess reactivity in a nuclear fission reactor.

Abstract: The invention refers to a method for operating a nuclear light water reactor during an operation cycle including a cardinal cycle and a number of successive control rod cycles. The reactor includes a plurality of elongated fuel units containing a nuclear fuel in the form a fissible material, a burnable absorber, and a plurality of control rods introduceable in a respective control rod position. Substantially all control rods are introduced in the core before the reactor is started and an operation cycle is initiated. The reactor is operated during the cardinal cycle with a first control rod configuration with a first group of control rods at least partly introduced and the remaining control rods extracted. The reactor is operated during the subsequent control rod cycles with a respective control rod configuration which each includes a different group of control rods at least partly introduced, wherein the cardinal cycle is substantially longer than each of the subsequent control rod cycles.

Abstract: It is presented, the method of stabilization and controlling of nuclear devices' parameters by means of usage of “absorbing shutter”. This method is based on usage of neutron's absorbing substance as “absorbing shutter” that split and shield active parts of nuclear device and may carry out the controlled changing own aggregate state for starting of initiation's process. When its aggregate state is changed, “absorbing shutter” can vary mechanical and physical parameters of a nuclear device's active main body. Prior to initiation, “absorbing shutter” holds the nuclear device into “below-critical configuration” and forms with parts of the nuclear device's active main body the monoblock that is not having significant hollow spaces. The hollow spaces' lacking gives to device mechanical properties of an incompressible solid body.

Abstract: An object of the present invention is to provide an accumulator including a flow damper which is capable of performing a control so that a vortex may not be formed in a vortex chamber at the time of a large flow injection without requiring huge labors and fabrication costs. The flow damper is configured of a colliding jet controller (a bevel or a projection) for controlling a colliding jet composed of a jet from a large flow pipe and a jet from a small flow pipe flowing into a vortex chamber at the time of a large flow injection so that the colliding jet may proceed directly to an outlet without forming a vortex in the vortex chamber. The colliding jet controller is provided at a junction of an inner surface of the small flow pipe and an inner surface of the vortex chamber.

Abstract: An object of the present invention is to provide an accumulator including a flow damper which is capable of performing a control so that a vortex may not be formed in a vortex chamber at the time of a large flow injection without requiring huge labors and fabrication costs. The flow damper is configured of a colliding jet controller (a bevel or a projection) for controlling a colliding jet composed of a jet from a large flow pipe and a jet from a small flow pipe flowing into a vortex chamber at the time of a large flow injection so that the colliding jet may proceed directly to an outlet without forming a vortex in the vortex chamber. The colliding jet controller is provided at a junction of an inner surface of the small flow pipe and an inner surface of the vortex chamber.

Abstract: In the present invention, a reactor power control apparatus of a natural circulation reactor comprises a reactor pressure vessel which circulates cooling water using the density difference of the coolant inside, a feed water pipe which is connected to the reactor pressure vessel and supplies cooling water, a power control section which controls the reactor power using a control rod. The feed water pipe has an ultrasonic thermometer sensor. Driving of the control rod is controlled by the power control section based on the feed water temperature detected by the feed water thermometer. The reactor power control apparatus can detect the temperature of the feed water and perform drive control of the control rod preferentially, and obtain stable reactor power.

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.