A printed circuit heat exchanger for use in a reactor includes a core formed from a stack of plates diffusion bonded together. The core has: a top face, a bottom face disposed opposite the top face, a first side face extending between the top face and the bottom face, and a second side face disposed opposite the first side face. The printed circuit heat exchanger includes: a plurality of primary channels defined in the core, each of the primary channels extending from a primary inlet defined in the first side face to a primary outlet defined in the second side face; and a plurality of secondary channels defined in the core, each of the secondary channels extending among at least some of the primary channels from a secondary inlet defined in the top face to a secondary outlet defined in the top face.

Methods of controlling the reactivity of a molten salt fission reactor. The molten salt fission reactor comprises a core and a coolant tank (101), the core comprising fuel tubes (103) containing a molten salt fissile fuel, and the coolant tank containing a molten salt coolant (102), wherein the fuel tubes are immersed in the coolant tank. The methods comprise dissolving a neutron absorbing compound in the molten salt coolant, the neutron absorbing compound comprising a halogen and a neutron absorbing element. The first method further comprises reducing the neutron absorbing compound to a salt of the halogen and an insoluble substance comprising the neutron absorbing element, the halogen being fluorine or chlorine, wherein the insoluble substance is not volatile at a temperature of the coolant during operation of the reactor. In the second method the one or more neutron absorbing compounds are chosen such that reduction of the neutron absorbing capacity of the one or more neutron absorbing compounds due to absorption of neutrons compensates for a fall in reactivity of the core in order to control fission rates in the core. Apparatus for implementing the methods are also provided.

Methods of controlling the reactivity of a molten salt fission reactor. The molten salt fission reactor comprises a core and a coolant tank (101), the core comprising fuel tubes (103) containing a molten salt fissile fuel, and the coolant tank containing a molten salt coolant (102), wherein the fuel tubes are immersed in the coolant tank. The methods comprise dissolving a neutron absorbing compound in the molten salt coolant, the neutron absorbing compound comprising a halogen and a neutron absorbing element. The first method further comprises reducing the neutron absorbing compound to a salt of the halogen and an insoluble substance comprising the neutron absorbing element, the halogen being fluorine or chlorine, wherein the insoluble substance is not volatile at a temperature of the coolant during operation of the reactor. In the second method the one or more neutron absorbing compounds are chosen such that reduction of the neutron absorbing capacity of the one or more neutron absorbing compounds due to absorption of neutrons compensates for a fall in reactivity of the core in order to control fission rates in the core. Apparatus for implementing the methods are also provided.

A sodium-cooled nuclear reactor includes at least one electromagnetic pump assembly and a backflow reduction pipe. The backflow reduction pipe may include an inlet, an outlet, at least one tubular section having a first length and a first diameter, and at least one fluid diode section between the inlet and the outlet.

A sodium-cooled nuclear reactor includes at least one electromagnetic pump assembly and a backflow reduction pipe. The backflow reduction pipe may include an inlet, an outlet, at least one tubular section having a first length and a first diameter, and at least one fluid diode section between the inlet and the outlet.

A nuclear reactor comprising: a moderator including a metal hydride; and a nuclear fuel in which europium is added as an additive to a main nuclear fuel material. Thus, the nuclear reactor can be kept in the subcritical state even under the state where all the control devices are pulled out before startup.

A nuclear reactor comprising: a moderator including a metal hydride; and a nuclear fuel in which europium is added as an additive to a main nuclear fuel material. Thus, the nuclear reactor can be kept in the subcritical state even under the state where all the control devices are pulled out before startup.

A liquid metal-cooled nuclear reactor includes, within a reactor pressure vessel having a reactor core, a multistage annular linear induction pump (ALIP) configured to circulate liquid metal coolant through the reactor core. The multistage ALIP includes multiple sets of induction coils that at least partially define separate, respective stages of the multistage ALIP. The multiple sets of induction coils are configured to be electrically connected to separate, respective polyphase power supplies, such that the stages of the multistage ALIP are configured to be controlled independently of each other to adjustably control a flow of liquid metal coolant through the reactor core based on independent control of the multiple polyphase power supplies.

A liquid metal-cooled nuclear reactor includes, within a reactor pressure vessel having a reactor core, a multistage annular linear induction pump (ALIP) configured to circulate liquid metal coolant through the reactor core. The multistage ALIP includes multiple sets of induction coils that at least partially define separate, respective stages of the multistage ALIP. The multiple sets of induction coils are configured to be electrically connected to separate, respective polyphase power supplies, such that the stages of the multistage ALIP are configured to be controlled independently of each other to adjustably control a flow of liquid metal coolant through the reactor core based on independent control of the multiple polyphase power supplies.

A nuclear reactor with forced-convection liquid coolant and solid fuel assemblies incorporates a heat removal system using a liquid metal bath for removing the nominal heat and phase-change material(s) (PCM) for removing the decay heat in an accident situation. The solid-fuel nuclear reactor with liquid metal or molten salt primary coolant simultaneously ensures heat removal by forced convection in the primary circuit, in normal and accident operating modes, during shutdown through the primary vessel of the reactor, that is, beyond the second containment barrier. In the event of an incident or accident, a compact passive decay heat removal system is capable of performing the safety function for a predetermined period, typically three days, without any intervention by an operator, due to the presence of one or more PCM(s) that store(s) the decay heat produced in the core and removed by the primary vessel.