Abstract: Upper internals for a nuclear reactor comprise an upper core plate and a plate which supports cluster guides tubes connecting the two plates together. The cluster guides project above the support plate. A bottom wall of the support plate is situated at a level just higher than the outlet nozzles of the reactor vessel and each guide is supported by the bottom wall of the support plate by abutment of a shoulder formed in a passage of the bottom wall, in the lower half thereof.

Abstract: A pressurized water reactor has a solid reflector formed of a stack of rings each completely surrounding the reactor core, whose internal periphery matches the external contour of the core. Keys fixed to the casing project into vertical grooves formed in the rings for centering them with respect to the core casing. The stack is formed with a plurality of vertical channels each consisting of a plurality of vertical mutually aligned passages each formed in a respective one of said rings, each channel containing a plurality of vertically aligned plugs.The vertical passages are formed in radially thicker parts only of the rings. Each plug cooperates with the respective ring to define an annular water flow channel. Some at least of the plugs comprise an upper flange bearing on a shoulder of a corresponding ring, machined for defining channels slanted with respect to the vertical so as to give a circumferential speed component to the water flowing along the annular passages about the plugs.

Abstract: A partitioning device is provided which can be used in a pressurized water nuclear reactor. It occupies the space between the prismatic shaped core of the reactor, and a cylindrical casing and comprises vertical partitioning plates surrounding the core and reinforcement elements placed between the partitioning plates and the casing. It comprises panels distributed into horizontal rows in vertical columns, all the panels of the same row being identical and having vertical partitioning plates welded together and fast with criss-crossed horizontal and vertical reinforcements bearing on the casing and with vertical tubes. The stacked tubes of a same column form a post resting on a core support plate. Solid vertical keys connect the panels in the different columns together and to the casing.

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: A device for wedging and positioning the upper support plate of the guides of control clusters in relation to a bearing surface linked to the vessel of a pressurized-water nuclear reactor, comprising an upper ring (22) and a lower ring (23) laid onto the cluster guide support plate (8) and the bearing surface (9), respectively, and between which is seated a stack of preloaded elastic washers (24). The device comprises a hollow connecting shank (26) with an axial channel (44) and passing through the two rings, to engage in a bore (20, 21) formed in the support plate or the bearing surface, the lower ring (23) being connectable to the shank, while the upper ring is mounted slidably relative to the lower ring (23) under the effect of the load exerted on the elastic washers.

Abstract: A device for the centering and fixation of a cluster guide flange and of a core plate of a nuclear reactor, extending parallel to one another in horizontal planes with a predetermined spacing. The device includes at least two axial guiding spindles of flange with respect to the core plate, diametrically opposite and rigidly connected to the plate or to the flange in order to engage into a housing in register formed in the flange or in the plate, respectively, and an assembly of self-locking shoes, adapted for sliding with a clearance within bores formed in the flange in order to be pressed on the plate surface, these shoes being each associated with a position control mechanism, carried by the flange and exerting on the shoes a force having a transverse component so as to cause, by reaction, immobilization of the flange with respect to the plate.

Abstract: Upper internals for a pressurized nuclear reactor include an assembly for collecting the coolant leaving the core and a separating device. The device has guides for the control clusters and their drive shafts, a lower plate formed with passages for the coolant leaving the core and an upper plate formed with holes for passage of the same coolant into the collection assembly or plenum. A peripheral shroud may connect the plates together. Each cluster guide of the flow separation device has an internal casing devoid of openings, having a practically coolant-tight connection with the plates, whereby the control clusters and their drive shafts are protected against the high speed coolant flow from the core to the outlet nozzle.

Abstract: The instrumentation arrangement comprises a horizontal plate (31) arranged below the vessel (1) closure head (3) through which instrumentation columns (27) pass, carrying measurement conduits internally (26). The distribution plate (31) carries vertical guide tubes (38), into each of which a measurement conduit (26) is introduced. Each of the vertical guide tubes (38) is engaged into a tubular brace (17) of the upper internal equipment of the reactor, to ensure the guidance of the measurement conduit (26), from the instrumentation column (27) to an instrumentation guide tube (30) of a reactor core assembly (5). The distribution plate (31) is fastened in a removable manner to the plate (18) supporting the upper internal equipment of the reactor and may be raised relative to the upper internal equipment for withdrawing, as a unit, the measurement conduits (26) from the instrumentation tubes of the core assemblies, when the closure head (3) is removed.

Abstract: A nuclear reactor is provided with an emergency cooling water injection device, comprising a vessel through which pass not only the cooling water inlet and outlet pipes under normal operating conditions but also a conduit for injecting pressurized water coming by an emergency reservoir, should a breakage of the primary circuit occur. A thermally insulated duct of the side wall of the vessel, at least at the level of the core, conveys the injected water below the core support plate.

Abstract: During a shutdown of the reactor, a device for partially closing off (27) the openings (26) of the reinforcements (6) located below the upper reinforcement (6a) is introduced through the opening (25) of the upper reinforcement (6a) of the partitioning of the core of the reactor. The closing off devices (27) remaining in position in the partitioning of the reactor after restarting thereof permit the increase and regulation of the head loss of the cooling water circulating in the annular space (7) around the partitioning (5) of the core. The closing-off device may consist of a rod (27) engaged in a set of openings (26) of the reinforcements (6) aligned along a vertical direction.

Abstract: A drive mechanism for a neutron absorbing bar of a liquid cooled nuclear reactor has a drive shaft movable within upper internals and a shock absorber. The shock absorber has a hydraulic cylinder arranged to bear on the upper internals, formed with a bore comprising an upper portion of larger diameter provided with discharge holes spaced longitudinally along the bore and with a lower portion of smaller diameter, a piston, movable within and along the cylinder, having a diameter corresponding to that of the upper portion and defining a shock absorbing chamber with the upper portion, the chamber having exhaust means comprising the discharge holes located to be progressively covered by the piston during downward movement thereof within the cylinder, and a resetting spring biasing the piston towards a top position where it uncovers the discharge holes.

Abstract: A pressurized water nuclear reactor with solid partitioning comprises a core formed by assemblies of prismatic shape disposed side by side inside a vertical cylindrical casing. A space between the core and the casing receives a solid partitioning structure. The partitioning is formed as a vertical stack of rings each completely surrounding the core, whose external periphery is engaged with a clearance in the casing and whose internal periphery matches the external contour of the core. The rings are centered and indexed with respect to the core casing by keys fixed to the casing and projecting into vertical grooves formed in the rings and they are formed with vertical mutually aligned holes defining cooling channels. Plugs in the channels define restricted water flow passages.