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: Device for guiding nuclear reactor control clusters consisting of several absorbing rods including guide casings, associated respectively with the various control clusters, and, inside each casing, horizontal plates (14) ensuring, in the upper part, discontinuous guidance at intermediate levels for the various elements of the control cluster. In the lower part of the casing, guidance of the rods arranged in pairs sharing one radius is achieved by combining horizontal plates (14) ensuring mechanical guidance of the rods with casings (22) which reduce the hydraulic effects to a minimum by calming the cooling fluid in the radial direction around the said absorbing rods. The invention applies to pressurized water nuclear reactors.

Abstract: The chamfering device comprises a frame to be centered and fixed coaxially within the pipe. A tool and its support are mounted concentrically around the frame and are movable along and about the axis in both translation and rotation by drive motors, and its position is detected and fixed before chamfering. The entire operation proceeds automatically without visual control or manual action, so that it can be performed in a radioactive environment.

Abstract: An emergency cooling device for a pressurized water nuclear reactor, through the injection of cooling liquid into the primary circuit of the reactor, comprising at least one double injection circuit equipped with two pumps arranged outside the safety enclosure of the reactor and a set of accumulators containing a certain amount of cooling liquid under pressure arranged inside the enclosure. The accumulators are distributed in a first set at a pressure P1 less than the pressure of the primary circuit of the reactor and a second set at the pressure P2 less than the pressure P1. The injection of cooling liquid through one and other set is caused by the automatic opening of valves when the pressure of the primary circuit drops below P1 and below P2, respectively, in the event of a leakage in this circuit. The invention is useful for pressurized water nuclear reactors having any number of primary loops.

Abstract: Apparatus for replacing thermal sleeves in pressurized-water nuclear power station circuits in a rapid, automatic manner producing minimal debris. A two-part frame is fixed to the outer wall of the sleeve coaxially therewith, each part of the frame carried one part of a two-part rotatable element, which in turn carries a support for a cross-cutting tool. The tool support is moved toward the axis of the frame but stopped just before the too breaks into the interior space of the sleeve.

Abstract: The reactor comprises a vessel closed by a lid and containing a core formed of fuel assemblies. The reactor comprises control clusters of two different types and an internal structure fixed inside the vessel, placed above the core and comprising means for guiding the clusters. The mechanisms associated with clusters of a first type each comprise a vertical cylinder belonging to the internal structure of the reactor, defining, with a piston from which is suspended a group of rods belonging to a cluster or forming a cluster, a work chamber. That chamber is connected by a duct, passing through the lid, to a valve for optional connection with a space at a pressure lower than that which prevails in the vessel.

Abstract: A process for circulating solid particles within a fluidization chamber, in which is formed a circulating fluidized bed comprising a dense lower zone (A) with a high concentration of particles, above which is located a dilute zone (B) containing particles carried along by the rising stream of a gas towards the upper part of the chamber (1), the latter opening into a circuit (4) for discharging the gases and particles, incorporating a device (41) for recovering the particles carried along, which is connected to the chamber (1) by means of a circuit (45) for recycling the recovered particles. In the upper part (12) of the fluidization chamber, the circulation speed of the cases is reduced before their discharge, so as to produce above the dilute zone (B) an upper zone (C) with a higher concentration of particles, in which some (35) of the particles escape from the stream of gas and fall in a shower along the side wall of the chamber, at the same time forming a descending annular film (34).

Abstract: The method according to the invention consists of sampling, at successive times separated by constant or non-constant time intervals, signals supplied by redundant channels measuring or calculating the parameter and validating a value of said parameter, as a function of a sample of N values of each channel, in which N.gtoreq.2. In a preferred manner, each sample of N values is modeled by a straight line using the method of least squares and the validated value of the parameter is worked out as a function of the inter-coherent models.

Abstract: A control device for a PWR includes a plurality of clusters arranged for insertion into and removal from the core and each having a plurality of rods connected to a common carrier vertically slidable in a stationary guide structure and connectable to a drive shaft. First clusters contain neutron absorbing material and are each individually associated with electromagnetic actuation means for adjusting the amount of insertion of the associated one of the first clusters. Second clusters contain a different material and are each individually associated with hydraulic actuation means controllable to cause upward and downward movement. A set of one first cluster and one second cluster is associated with some of said fuel assemblies, with the drive shafts of the two clusters in each set being arranged symmetrically with respect to the axis of a single stationary structure located above the associated fuel assembly and arranged for authorizing mutually independent movement of the first and second clusters.

Abstract: Fuel array for an undermoderated nuclear reactor, comprising rods (6) arranged in a prism-shaped casing (1) parallel to the height of this casing (1). The internal surface of each of the walls (2) of the casing (1) is provided with channels (5) each of the channels (5) is located opposite a rod (6) arranged at the periphery of the array. The projecting parts (9) of the walls (2), between two channels (5), occupy part of the space between two peripheral rods (6). In this way, the moderating level remains constant throughout the cross-section of the array.The invention applies, in particular, to pressurized water reactors.

Abstract: A modular lining for adapting the containment to the core of a pressurized water nuclear reactor, consisting of juxtaposed modular blocks (5) placed between the core containment (1) and the outer surface of the core (3). Arranged between the adjacent faces of the blocks (5), there are thin packing pieces (8) maintaining a certain gap between the undrilled solid blocks (5). The blocks (5) are fixed non-contiguously to the core containment (1) by screw devices (10) cooled by water circulation. The invention applies in particular to pressurized water nuclear reactors of improved efficiency and with a varying neutron spectrum.

Abstract: The invention relates to an underwater measuring device of the hardness of a vertical wall of the partitioning of the core of a pressurized water nuclear reactor. The device comprises a hollow pole for the manipulation from the edge of the pool of the reactor of the pole in vertical position. A body fast to the pole at its lower end contains a first chamber in which is mounted a movable piston bearing support means intended to come into contact with walls at right angles and a second chamber in which is movably mounted a second piston bearing a hardness measuring head designed to form an impression on the wall opposite one of the walls. Hydraulic fluid supply means for the chambers and conductors pass through the hollow pole. The conductors are connected to a measuring station. The invention is applicable particularly to determining the influence of irradiation on the walls of the partitioning of a nuclear reactor, after a certain period of operation.

Abstract: Device for centering and guiding a roller for supporting a massive component, incorporating, on each bearing face of the supporting components, two centering surfaces and at least one rack which are arranged in the direction of movement of the roller. The centering surfaces and the rack which are associated with one bearing face are placed opposite the centering components and the rack associated with the opposite bearing face. The roller incorporates the cylindrical roller wheels and at least one pinion in positions corresponding to the centering surfaces and the rack. The invention applies, in particular, to anti-earthquake bearing devices for a housing for storage of nuclear fuel assemblies.

Abstract: Method and installation for processing a material in a circulating fluidized bed, in which, in the filtration compartment (4) traversed by the fluidization gas at a speed which is so regulated as to put into suspension only the particles having dimensions smaller than a given limit, the unburnt largest particles (25) which are recovered and are directly recycled in the fluidized bed (21) and the fine particles (24) are subjected in an adjacent compartment (5) to a processing for agglomerating the ashes by forming in the processing compartment (5) a high temperature zone (96), the agglomerated ashes (26) being withdrawn at the base of the processing compartment (5) and the unburnt fine particles (27) being returned to fluidized bed (21) through a recycling circuit (54).

Abstract: Process and apparatus for ultrafiltration of the cooling water of a pressurized water nuclear reactor, during operation of the reactor. A fraction of the flow of pressurized water is withdrawn continuously in at least one cold branch (8) of the primary circuit (2). This withdrawn water is circulated, while it is still at the temperature and pressure of the primary circuit (2), in contact with the entry face of an ultrafiltration wall (40). The filtrate is withdrawn at a pressure which is less than 15 bars lower than the primary water pressure. The concentrate is kept in circulation with the entry face of the wall (40). The wall (40) can consist of an assembly of tubes maintained between two tube plates. The invention applies to pressurized water nuclear reactors whatever the number of primary circuit loops.

Abstract: Device for operating a cluster of neutron absorber elements in a pressurized water nuclear reactor, comprising two coaxial control shafts (2, 3), the central shaft (3) being rigidly joined to the cluster of absorber elements. A widened part (22) of this shaft (3) forms a piston (22) which is fitted with segments (35). A pressure difference on either side of a segment (35) permits the clusters of absorber elements to be lifted by acting on the piston (22). The segment (35) is radially expandable and the leaktight sealing of the segment is initiated by entry of the piston (22) into the reduced diameter zone (10) of the shaft (2). The invention applies, in particular, to nuclear reactors with spectral shift employing clusters of fertile elements.

Abstract: Process of replacing a sleeve mounted within a pipe, and devices for carrying out that process. The process consists in making a pair of cross cuts in the pipe (1'), withdrawing the section thus obtained and the sleeve (5'), machining chamfers on the free ends of the pipe (1'), checking the position and the geometry of the blocks (6'), welding into the gap in the pipe (1') a new section, onto the internal wall of which one of the ends of a new sleeve (5') has previously been welded. The invention can be applied to the circuits of pressurized-water nuclear power stations.

Abstract: Installation for electric connection of devices placed inside the containment of a PWR, comprising a first cable associated with each electric device, extending from the device and connected to a fixed connector installed above the cover of the reactor vessel. A second cable is connected to the connector and to a connector fixed to a plate remote from the reactor vessel. Each second cable is formed from several sections including a first section for connection to the fixed connector above the cover and to a lead-in connector at the end of a leak tight conduit installed horizontally above the cover and a second section inside the conduit. A third section is adapted for connection to a lead-out connector from the conduit and to the connector fixed to the plate at a distance from the reactor.

Abstract: A device and process for fixing two parts with a captive screw (5) engaged in a threaded hole (3) machined in at least one of the two parts (1,2). The screw (5) comprises over its whole length a bore (6) communicating with at least one radially directed hole (10) opening out on the outer side surface of the screw (5) in its threaded part (5a) and enclosing a component (11) movable in the hole (10). A maneuvering rod (14) is engaged in the bore (6) for locking the screw (5) in place in the threaded hole (3), by placing a part of the rod with larger diameter to coincide with the component (11) which then crushes the threading of the part (3a) of the hole (3). The rod (14) is crimped over the screw (5) by virtue of strips (18). The disclosure applies in particular to the assembly of two walls of a partitioning of the core of a pressurized water nuclear reactor.

Abstract: The invention relates to a temporary sealing obturation panel, inside a vessel accessible only through a manhole, of a passage provided on its periphery with a support collar. It is constituted by: panels articulated by flexible fluid-tight hinges, bordered by lines of latching pins, stiffeners comprising lines of holes conjugate with the lines of pins, a frame in at least two articulated parts, with means for gripping the ends of the panels and the stiffeners against the support collar. The invention is applicable to the closing of primary circuit ducts opening into the water box of a steam generator of a pressurized water nuclear boiler.