Abstract: A fast nuclear reactor, provided with a protection system for shutdown of the reactor in accidental conditions and comprising shutdown devices that surround the core of the reactor and have an upper volume and a lower volume separated by a septum. The upper volume contains an operating fluid partly facing the active part of the core with neutron reflecting function to facilitate reaching the critical mass of the reactor. The lower volume contains a neutron transparent medium (for example gas) or a neutron absorbing medium (for example boron carbide balls immersed in the primary coolant). Replacement in the volume of the neutron reflecting medium with a neutron transparent or absorbing medium reduces the reactivity of the reactor and causes its shutdown.

Abstract: A nuclear reactor cooled by liquid metal or by molten salts, provided with a heat exchanger, having inlet of the primary fluid in the lower part and circumferential outlet window in the vicinity of the free surface of the primary fluid in the cold collector. The outlet window is located in an intermediate position with respect to the tube bundle partially raised with respect to the free surface in the cold collector and supplied with primary fluid throughout its height by means of an ancillary device for creating an underpressure in the cover gas of the exchanger with respect to the cover gas in the vessel. The raising of the exchanger and the positioning of the outlet window in the vicinity of the free surface of the primary coolant help to minimize the displacement of primary fluid in the event of accidental release of secondary fluid inside the heat exchanger.

Abstract: One or more embodiments of the present invention relate to a pump/heat exchanger assembly of a nuclear reactor, in particular a liquid metal cooled nuclear reactor, the pump being characterized in that the shaft for driving the impeller is inserted in an shell inside the heat exchanger and has a smaller cross section at the bottom part of the tube bundle of the heat exchanger and a cross section that gradually increases up to a widest cross section at the top part of the tube bundle of the heat exchanger. The resulting axial profile of the impeller's shaft is, at the same time, designed to uniformly distribute the flow of the primary fluid inside the tube bundle of the heat exchanger and to provide high mechanical inertia to the pump.

Abstract: A nuclear reactor is provided that comprises a vessel that houses a core, comprising a bundle of fuel elements, and immersed in a primary cooling fluid of the core; the fuel elements extend along respective longitudinal and parallel axes and are mechanically supported by respective heads joined to each other and joined to an anchoring structure by support devices acting between adjacent fuel elements, or acting between fuel elements situated on the periphery of the core and the anchoring structure, and which constitute an integral part of the heads of the fuel elements.

Abstract: The present invention concerns a nuclear reactor, preferably a pool-type nuclear reactor cooled by liquid metal or molten salts, having a core formed of a bundle of fuel elements and immersed in a primary fluid for cooling the core; the fuel elements are provided with expanders acting in a direction perpendicular to the axes of the fuel elements and having low thermal expansion elements which engage alternatively with high thermal expansion elements to amplify the radial expansion of respective end elements which, when a predetermined temperature is exceeded, engage with each other and space the fuel elements from one another and in particular their active part to introduce negative reactivity into the core.

Abstract: The invention concerns a nuclear reactor comprising a vessel closed at the top by a radially external fixed closing structure and by a radially internal mobile closing structure. The vessel contains a core immersed in a primary cooling fluid and comprising fuel elements, control rods, shutdown rods, and a hydraulic separation structure delimiting a hot manifold and a cold manifold in which the primary fluid circulates. The control rods and the shutdown rods are inserted in respective penetrations of the fixed closing structure and are therefore located radially external to the mobile closing structure and external to an upper portion of the separation structure containing respective heads of the fuel elements.

Abstract: The present invention concerns a nuclear reactor, preferably a pool-type nuclear reactor cooled by liquid metal or molten salts, having a core formed of a bundle of fuel elements and immersed in a primary fluid for cooling the core; the fuel elements are provided with expanders acting in a direction perpendicular to the axes of the fuel elements and having low thermal expansion elements which engage alternatively with high thermal expansion elements to amplify the radial expansion of respective end elements which, when a predetermined temperature is exceeded, engage with each other and space the fuel elements from one another and in particular their active part to introduce negative reactivity into the core.

Abstract: The invention concerns a nuclear reactor, comprising a vessel closed at the top by a radially external fixed closing structure and by a radially internal mobile closing structure and containing a core, immersed in a primary cooling fluid and comprising fuel elements and control and shutdown rods, and a hydraulic separation structure delimiting a hot manifold and a cold manifold in which the primary fluid circulates; the control rods and shutdown rods are inserted in respective penetrations of the fixed closing structure and are therefore located radially external to the mobile closing structure and external to an upper portion of the separation structure containing respective heads of the fuel elements.

Abstract: A system for evacuating the residual heat from a nuclear reactor comprises: a first heat exchanger, which transfers heat from a primary fluid of the reactor to a secondary fluid; a second heat exchanger, where the secondary fluid is cooled by an auxiliary fluid which crosses a cooling duct; and a control portion, subject to thermal expansion by effect of the heating, induced by an increase in the temperature of the primary fluid beyond a preset threshold, of the secondary fluid in the control portion; the control portion being connected to a mechanical actuator device moved by the thermal expansion of the control portion to open the cooling duct and allow the passage of auxiliary fluid into the cooling duct and through the second heat exchanger.

Abstract: The present invention relates to a nuclear reactor (1), in particular a liquid-metal-cooled reactor, provided with a separation structure (5) between hot header (6) and cold header (7), narrower in the upper portion (16) for containment of the headers of the fuel assemblies and wider in the lower element (14) at the active part (4) of the core, with a variously shaped connecting element (15) between the lower element (14) and the upper element (16), and with heat exchangers (11) positioned between the upper portion (16) of said separation structure (5) and the reactor vessel (2), which engage on the connecting element (15) via vertical ducts (20) for being fed with hot primary fluid leaving the core (4).

Abstract: One or more embodiments of the present invention relate to a pump/heat exchanger assembly of a nuclear reactor, in particular a liquid metal cooled nuclear reactor, the pump being characterized in that the shaft for driving the impeller is inserted in an shell inside the heat exchanger and has a smaller cross section at the bottom part of the tube bundle of the heat exchanger and a cross section that gradually increases up to a widest cross section at the top part of the tube bundle of the heat exchanger. The resulting axial profile of the impeller's shaft is, at the same time, designed to uniformly distribute the flow of the primary fluid inside the tube bundle of the heat exchanger and to provide high mechanical inertia to the pump.

Abstract: A nuclear reactor is provided that comprises a vessel that houses a core, comprising a bundle of fuel elements, and immersed in a primary cooling fluid of the core; the fuel elements extend along respective longitudinal and parallel axes and are mechanically supported by respective heads joined to each other and joined to an anchoring structure by support devices acting between adjacent fuel elements, or acting between fuel elements situated on the periphery of the core and the anchoring structure, and which constitute an integral part of the heads of the fuel elements.

Abstract: A nuclear reactor cooled by liquid metal or by molten salts, provided with a heat exchanger, having inlet of the primary fluid in the lower part and circumferential outlet window in the vicinity of the free surface of the primary fluid in the cold collector. The outlet window is located in an intermediate position with respect to the tube bundle partially raised with respect to the free surface in the cold collector and supplied with primary fluid throughout its height by means of an ancillary device for creating an underpressure in the cover gas of the exchanger with respect to the cover gas in the vessel. The raising of the exchanger and the positioning of the outlet window in the vicinity of the free surface of the primary coolant help to minimize the displacement of primary fluid in the event of accidental release of secondary fluid inside the heat exchanger.

Abstract: The present invention relates to a nuclear reactor (1), in particular a liquid-metal-cooled reactor, provided with a separation structure (5) between hot header (6) and cold header (7), narrower in the upper portion (16) for containment of the headers of the fuel assemblies and wider in the lower element (14) at the active part (4) of the core, with a variously shaped connecting element (15) between the lower element (14) and the upper element (16), and with heat exchangers (11) positioned between the upper portion (16) of said separation structure (5) and the reactor vessel (2), which engage on the connecting element (15) via vertical ducts (20) for being fed with hot primary fluid leaving the core (4).

Abstract: A system (10) for evacuating the residual heat from a nuclear reactor (1) comprises: a first heat exchanger (11), which transfers heat from a primary fluid (5) of the reactor (1) to a secondary fluid (15); a second heat exchanger (12), where the secondary fluid (15) is cooled by an auxiliary fluid (16) which crosses a cooling duct (17); and a control portion (40), subject to thermal expansion by effect of the heating, induced by an increase in the temperature of the primary fluid (5) beyond a preset threshold, of the secondary fluid (15) in the control portion (40); the control portion (40) being connected to a mechanical actuator device (32) moved by the thermal expansion of the control portion (40) to open the cooling duct (17) and allow the passage of auxiliary fluid (16) into the cooling duct (17) and through the second heat exchanger (12).

Abstract: A nuclear reactor cooled with pressurized water, having a pressurized tank installed in which are compact steam generators; each steam generator comprises a plurality of heat-exchange tubes having respective spiral portions set in levels on top of one another to form at least one annular tube bundle delimiting a substantially cylindrical internal central zone, pre-arranged for supply from above with primary water, which then traverses the tube bundle radially.

Abstract: The present invention relates to a nuclear reactor, in particular a pool-type nuclear reactor cooled with liquid metal (for example, a heavy metal such as lead or lead-bismuth eutectic) or with sodium or molten salts, having a core formed by a bundle of fuel elements and immersed in a primary fluid circulating between the core and at least one heat exchanger; the fuel elements extend along respective parallel longitudinal axes and have respective bottom active parts immersed in the primary fluid to constitute the core, and respective service parts that extend at the top from the active parts and emerge from the primary fluid; the fuel elements are mechanically supported via respective top end heads anchored to supporting structures and can be operated via handling machines.

Abstract: A nuclear reactor cooled with pressurized water, having a pressurized tank installed in which are compact steam generators; each steam generator comprises a plurality of heat-exchange tubes having respective spiral portions set in levels on top of one another to form at least one annular tube bundle delimiting a substantially cylindrical internal central zone, pre-arranged for supply from above with primary water, which then traverses the tube bundle radially.

Abstract: The present invention relates to a nuclear reactor, in particular a pool-type nuclear reactor cooled with liquid metal (for example, a heavy metal such as lead or lead-bismuth eutectic) or with sodium or molten salts, having a core formed by a bundle of fuel elements and immersed in a primary fluid circulating between the core and at least one heat exchanger; the fuel elements extend along respective parallel longitudinal axes and have respective bottom active parts immersed in the primary fluid to constitute the core, and respective service parts that extend at the top from the active parts and emerge from the primary fluid; the fuel elements are mechanically supported via respective top end heads anchored to supporting structures and can be operated via handling machines.

Abstract: A system for evacuating the residual heat from a nuclear reactor cooled with liquid metal or molten salts has two types of heat exchangers immersed in the primary fluid of the reactor: heat exchangers with higher power density, which use boiling water as secondary cooling fluid and are particularly suitable for evacuating the residual heat in the first days after turning-off of the reactor; and heat exchangers operating with atmospheric air or with water and suitable for evacuating the residual heat for indefinite periods of time.