Abstract: A passive nuclear reactor control device. The passive nuclear reactor control device comprises a sealed chamber, which comprises a reservoir and a tube in fluid communication with the reservoir. A molten salt is within the sealed chamber, the molten salt being a eutectic mixture of a monovalent metal halide, and a fluoride or chloride of one or more lanthanides and/or a fluoride or chloride of hafnium. A gas is within the sealed chamber, and the gas does not react with the molten salt.

Abstract: Use of a molten salt comprising aluminium trifluoride and sodium fluoride as a primary coolant for a fission reactor, wherein the molten salt is in contact with graphite and with aluminium metal during operation of the fission reactor.

Abstract: A passive nuclear reactor control device. The passive nuclear reactor control device comprises a sealed chamber, which comprises a reservoir and a tube in fluid communication with the reservoir. A molten salt is within the sealed chamber, the molten salt being a eutectic mixture of a monovalent metal halide, and a fluoride or chloride of one or more lanthanides and/or a luoride or chloride of hafnium. A gas is within the sealed chamber, and the gas does not react with the molten salt.

Abstract: A heat exchanger. The heat exchanger comprises a plurality of primary fluid tubes configured to carry a primary fluid, a plurality of secondary fluid tubes configured to carry a secondary fluid, and a plurality of intervening layers, each intervening layer being thermally conductive and impermeable to both the primary and secondary fluids. Each intervening layer has one or more of the primary fluid tubes on a first side, and one or more of the secondary fluid tubes on a second side opposite the first side, such that the region between each pair of neighbouring intervening layers contains either primary fluid tubes or secondary fluid tubes, but not both primary and secondary fluid tubes.

Abstract: A molten salt fission reactor. The reactor includes a reactor core, which includes a plurality of fuel tubes. Each fuel tube contains a fuel salt and a gas interface. The fuel salt is a molten salt of one or more fissile isotopes. The gas interface is a surface of the fuel salt in contact with a gas space during operation of the reactor. The reactor also includes a fuel salt cooling system, which is configured to cool the fuel salt. The cooling system includes a heat exchanger and a coolant tank. The coolant tank contains a coolant liquid in which the fuel tubes are at least partially immersed. The heat exchanger is for extracting heat from the coolant liquid.

Abstract: Spent nuclear fuel is added to an electro-reduction cell, wherein the electro-reduction cell includes a halide salt electrolyte, and anode, and a cathode including an alloy of uranium and a first metal forming a low melting point alloy with uranium, the first metal being one or more of: iron; chromium; nickel; manganese; and cobalt. The spent nuclear fuel is electrochemically reduced at a potential sufficient to reduce plutonium and lanthanides in the spent nuclear fuel, to form a molten alloy of the first metal, uranium and higher actinides present in the spent nuclear fuel. The alloy is extracted from the electro-reduction cell while uranium oxide is present in the electro-reduction cell. The spent nuclear fuel includes uranium oxide and at least 1 mol of lanthanides per tonne of uranium in the spent nuclear fuel, and the electro-reduction cell is operated at a temperature above the melting point of the alloy.

Abstract: Spent nuclear fuel is added to an electro-reduction cell, wherein the electro-reduction cell includes a halide salt electrolyte, and anode, and a cathode including an alloy of uranium and a first metal forming a low melting point alloy with uranium, the first metal being one or more of: iron; chromium; nickel; manganese; and cobalt. The spent nuclear fuel is electrochemically reduced at a potential sufficient to reduce plutonium and lanthanides in the spent nuclear fuel, to form a molten alloy of the first metal, uranium and higher actinides present in the spent nuclear fuel. The alloy is extracted from the electro-reduction cell while uranium oxide is present in the electro-reduction cell. The spent nuclear fuel includes uranium oxide and at least 1 mol of lanthanides per tonne of uranium in the spent nuclear fuel, and the electro-reduction cell is operated at a temperature above the melting point of the alloy.

Abstract: There is described a method of reprocessing spent nuclear fuel. The spent nuclear fuel is added to an electro-reduction cell containing a halide salt electrolyte at a temperature above the melting point of the metallic form of uranium and higher actinides present in the spent nuclear fuel. The cell is operated so as to electrochemically reduce the spent nuclear fuel to an alloy of uranium and higher actinides present in the spent nuclear fuel, wherein electrochemical reduction is continued until a concentration of unreduced components of the spent nuclear fuel is sufficiently low for the ahoy to agglomerate.

Abstract: There is described a method of reprocessing spent nuclear fuel. The spent nuclear fuel is added to an electro-reduction cell containing a halide salt electrolyte at a temperature above the melting point of the metallic form of uranium and higher actinides present in the spent nuclear fuel. The cell is operated so as to electrochemically reduce the spent nuclear fuel to form an alloy of uranium and higher actinides present in the spent nuclear fuel, wherein electrochemical reduction is continued until a concentration of unreduced components of the spent nuclear fuel is sufficiently low for the alloy to agglomerate.

Abstract: 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.

Abstract: According to a first aspect, there is provided a nuclear fission reactor. The nuclear fission reactor comprises a core, a tank surrounding the core, and a cooling system located outside the tank. The cooling system comprises one or more structures configured to absorb thermal radiation emitted from an outer wall of the tank. The structures are not substantially thermally coupled to the tank except by radiation. The cooling system further comprises a cold air inlet and a hot air outlet, positioned such that air flows from the cold air inlet to the hot air outlet over, around and/or through the one or more structures.

Abstract: A method of operating a nuclear fission reactor, the reactor comprising a reactor core, and a coolant tank containing coolant, the reactor core comprising an array of fuel assemblies arranged in generally parallel rows, each fuel assembly comprising one or more fuel tubes containing fissile fuel. For each row of the array, one or more spent fuel assemblies are removed from the array at a second end of the row, fuel assemblies are moved along the row from a first end to the second end; and one or more fuel assemblies are introduced to the array at the first end of the row. Each fuel assembly remains within a single row while the fuel assembly is within the array. At least the fuel-filled portions of the fuel tubes of each fuel assembly are immersed in the coolant while the fuel assembly is within the array.

Abstract: A molten halide salt mixture for use in a nuclear fission reactor. The molten halide salt mixture comprises a reactive metal halide salt. The reactive metal halide salt is a halide salt of a reactive metal. The reactive metal has a Pauling electronegativity of at least 1.2, and at least one other halide salt of higher valence than the reactive metal halide salt. The reactive metal salt is at a concentration sufficient to prevent corrosion of metals in contact with the molten halide salt mixture and insufficient to cause deposition of the reactive metal at an operating temperature of the nuclear fission reactor.

Abstract: A nuclear fission reactor comprising a core, a pool of coolant liquid, and a heat exchanger. The core comprises an array of hollow tubes which contain molten salts of fissile isotopes. The tube array is at least partly immersed in the pool of coolant liquid. The tube array comprises a critical region, where the density of the fissile isotopes during operation of the reactor is sufficient to cause a self-sustaining fission reaction. Heat transfer from the molten salts of fissile isotopes to the tubes is achieved by any one or more of natural convection of the molten salts, mechanical stirring of the molten salts, and oscillating fuel salt flow within the tubes. The molten salts of fissile isotopes are contained entirely within the tubes during operation of the reactor.

Abstract: Use in a nuclear fission reactor of a sacrificial metal in a molten salt fuel containing actinide halides in order to maintain a predefined ratio of actinide trihalide to actinide tetrahalide without reducing actinide trihalide to actinide metal. A method of maintaining oxidation state of a molten salt containing actinide halides. The method comprises contacting the molten salt continuously with a sacrificial metal, the sacrificial metal being selected in order to maintain a predefined ratio of actinide trihalide to actinide tetrahalide without reducing actinide trihalide to actinide metal. A fuel tube containing a sacrificial metal is also described.

Abstract: 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.

Abstract: A method of operating a nuclear fission reactor. The reactor comprises a reactor core, and a coolant tank containing coolant, the reactor core comprises an array of fuel assemblies. Each fuel assembly extends generally vertically and comprises one or more fuel tubes containing fissile fuel. The fuel tubes are immersed in the coolant. The method comprises monitoring and/or modelling fuel concentrations and/or fission rates in each of the fuel assemblies; and in dependence upon results of the monitoring and/or modelling, moving fuel assemblies horizontally within the array, without lifting the fuel tubes from the coolant, in order to control fission rates in the reactor core. A nuclear reactor implementing the method, and fuel assemblies for use in the method are also disclosed.

Abstract: Use in a nuclear fission reactor of a sacrificial metal in a molten salt fuel containing actinide halides in order to maintain a predefined ratio of actinide trihalide to actinide tetrahalide without reducing actinide trihalide to actinide metal. A method of maintaining oxidation state of a molten salt containing actinide halides. The method comprises contacting the molten salt continuously with a sacrificial metal, the sacrificial metal being selected in order to maintain a predefined ratio of actinide trihalide to actinide tetrahalide without reducing actinide trihalide to actinide metal. A fuel tube containing a sacrificial metal is also described.

Abstract: A nuclear fission reactor comprising a core, a pool of coolant liquid, and a heat exchanger. The core comprises an array of hollow tubes which contain molten salts of fissile isotopes. The tube array is at least partly immersed in the pool of coolant liquid. The tube array comprises a critical region, where the density of the fissile isotopes during operation of the reactor is sufficient to cause a self-sustaining fission reaction. Heat transfer from the molten salts of fissile isotopes to the tubes is achieved by any one or more of natural convection of the molten salts, mechanical stirring of the molten salts, and oscillating fuel salt flow within the tubes. The molten salts of fissile isotopes are contained entirely within the tubes during operation of the reactor.

Abstract: A method for evaluating a quality of a seismic inversion. The method includes performing a first match between seismic data and borehole seismic data at one or more borehole locations to generate an estimate of a wavelet in the seismic data. The method then performs a seismic inversion on the seismic data using the estimate of the wavelet to generate inverted seismic data. After performing the seismic inversion, the method converts the inverted seismic data into one or more reflectivity traces. The method then includes performing a second match between the one or more reflectivity traces and one or more traces in the seismic data and performing a third match between the one or more reflectivity traces and one or more traces in the borehole seismic data. After performing the second and third matches, the method determines the quality of the seismic inversion based on the first match, the second match, the third match or combinations thereof.