The invention relates to the field of nuclear engineering, and more particularly to designs for removable neutron reflector blocks for heavy liquid metal-cooled fast neutron reactors. The present fast neutron reactor contains a core consisting of heavy liquid metal-cooled fuel rods, and neutron reflector blocks, disposed around the core, which comprise a steel casing with at least one inlet opening in the side walls thereof above the core boundary, said inlet opening being intended for diverting part of the coolant flow from the space between the blocks into the casing, and at least one vertical pipe mounted in the casing, through which the diverted coolant flow, which has passed through the upper and lower boundaries of the core, enters the bottom part of the casing; also, on the outer side of the casing, above the inlet opening, there is mounted a throttling device for creating hydraulic resistance to the coolant flow in the space between the blocks. The technical result is an increase in the operating safety and the performance of a fast neutron reactor and a reduction in the heat exchange surface of the steam generator.

A nuclear engine system includes: a pump configured to pump a propellant; a fuel element including a set of nuclear fuel particles; a moderator configured to surround the fuel element and defining a set of moderator coolant channels configured to cool the moderator; a reflector including a neutron-reflecting material and a reflector coolant channel arranged within the reflector to cool the reflector, the reflector configured to at a first time, operate in a closed configuration to reflect neutrons to the fuel element to increase an energy flux, and at a second time, operate in an open configured to leak neutrons out of the engine system to decrease the energy flux; and a thrust nozzle configured to outlet propellant from the fuel element to produce thrust including a nozzle coolant channel arranged within a wall of the thrust nozzle configured to cool the nozzle.

A nuclear engine system includes: a pump configured to pump a propellant; a fuel element including a set of nuclear fuel particles; a moderator configured to surround the fuel element and defining a set of moderator coolant channels configured to cool the moderator; a reflector including a neutron-reflecting material and a reflector coolant channel arranged within the reflector to cool the reflector, the reflector configured to at a first time, operate in a closed configuration to reflect neutrons to the fuel element to increase an energy flux, and at a second time, operate in an open configured to leak neutrons out of the engine system to decrease the energy flux; and a thrust nozzle configured to outlet propellant from the fuel element to produce thrust including a nozzle coolant channel arranged within a wall of the thrust nozzle configured to cool the nozzle.

Provided is a nuclear reactor unit that can reduce a temperature increase in a reactor core at the occurrence of an abnormality with a simple structure. Included are a reactor core having radioactive fuel and causing the radioactive fuel to cause a nuclear reaction and a nuclear reactor vessel housing the reactor core and hermetically sealing the reactor core. The nuclear reactor vessel includes an inner shroud covering the entire periphery of the reactor core and an outer shroud covering the entire periphery of the inner shroud. A first space formed by the outer shroud and the inner shroud is in a vacuum condition. The inner shroud includes a main body and a communicating part placed in part of the main body and communicating the first space to a second space, which is a space inside the inner shroud, when the reactor core reaches a threshold temperature or higher.