Method for the manufacture of Radium-225-containing material from Radium-226-containing materials by subjecting a starting material containing Radium-226 to neutron irradiation from a nuclear reactor to convert .sup.226Ra into Radium-225 to provide a Radium-225-containing material, characterised in that the neutron irradiation of Radium-226-containing starting material is performed in a moderated nuclear reactor; and the Radium-226-containing starting material is shielded with a thermal neutron absorption shield.

Method for the manufacture of Radium-225-containing material from Radium-226-containing materials by subjecting a starting material containing Radium-226 to neutron irradiation from a nuclear reactor to convert .sup.226Ra into Radium-225 to provide a Radium-225-containing material, characterised in that the neutron irradiation of Radium-226-containing starting material is performed in a moderated nuclear reactor; and the Radium-226-containing starting material is shielded with a thermal neutron absorption shield.

A control rod for a nuclear fuel assembly is described herein that includes a neutron absorbing material having a melting point greater than 1500° C. that does not form a eutectic with a melting point less than 1500° C., and may further include a cladding material having a melting point greater than 1500° C. The cladding material is selected from the group consisting of silicon carbide, zirconium, a zirconium alloy, tungsten, and molybdenum. The absorbing material is selected from the group consisting of Gd.sub.2O.sub.3, Ir, B.sub.4C, Re, and Hf. The metal cladding or the absorbing material may be coated with an anti-oxidation coating of Cr with or without a Nb intermediate layer.

The reactor core includes at least one module, solid and liquid neutron moderators. The module contains a casing, at least one heat pipe, one fuel element and thermal insulation. The heat pipe is in the shape of a casing with a wick and contains a coolant. The fuel element is made of nuclear fuel, arranged in the evaporation area of the heat pipe around its casing in thermal contact with it, and enclosed in a can. Low-melting metals with a high boiling point are used as the coolant of the heat pipe. Thermal insulation is arranged between the can and the casing of the module. At least one hole is made in the solid neutron moderator, in which at least one module is arranged. The space between the casing of the module and the solid neutron moderator is filled with a liquid neutron moderator.

A method and apparatus for extending the period a nuclear steam supply system spent fuel pool can be safely passively cooled by storing the spent fuel offloaded from the reactor, in the containment for one reactor operating cycle. During a refueling the spent fuel that is not to be returned to the reactor and the spent fuel that will be returned to the reactor are stored separately in shielded locations within the containment. After one operating cycle, the spent fuel stored within the containment that was not returned to the reactor just prior to the last operating cycle, is offloaded to the spent fuel pool and replaced by the newly offloaded spent fuel that is being retired.

Disclosed is an entropy-controlled solid solution matrix BCC alloy having strong resistance to high-temperature neutron radiation damage. The entropy-controlled solid solution matrix BCC alloy includes three or more multicomponent main elements selected from the element group consisting of Zr, Al, Nb, Mo, Cr, V, and Ti selected based on a neutron absorption cross-sectional area and a mixing enthalpy. Each of the elements is included in an amount of 5 to 35 at %, and the entropy-controlled solid solution matrix BCC alloy is a BCC-structure solid solution matrix alloy in a medium-entropy to high-entropy state. In this invention, damage caused by neutron radiation is reduced, and entropy is controlled to thus ensure a solid solution matrix BCC structure having a slow diffusion speed, and accordingly, resistance to void swelling due to radioactive rays is high.

This disclosure describes various configurations and components of a molten fuel fast or thermal nuclear reactor in which one or more primary heat exchangers are located above the reactor core of the nuclear reactor.

The fuel cartridge may include a plurality of fuel channels, a first header disposed on a first side of a fuel matrix, a second header disposed on a second side of the fuel matrix opposite to the first side, and a plurality of cooling tubes through which a working fluid flows. Each of the plurality of cooling tubes may pass through each corresponding cooling channel of the plurality of cooling channels, where each of the plurality of cooling tubes has a first end connected to the first header and a second end connected to the second header. The fuel cartridge may include an interior space for sealingly containing the fuel matrix may include a pressure boundary independent from an interior of the plurality of cooling tubes, such that the interior space is not in fluid communication with the plurality of cooling tubes.

The fuel cartridge may include a plurality of fuel channels, a first header disposed on a first side of a fuel matrix, a second header disposed on a second side of the fuel matrix opposite to the first side, and a plurality of cooling tubes through which a working fluid flows. Each of the plurality of cooling tubes may pass through each corresponding cooling channel of the plurality of cooling channels, where each of the plurality of cooling tubes has a first end connected to the first header and a second end connected to the second header. The fuel cartridge may include an interior space for sealingly containing the fuel matrix may include a pressure boundary independent from an interior of the plurality of cooling tubes, such that the interior space is not in fluid communication with the plurality of cooling tubes.

A nuclear reactor vessel includes a shell (5) having a wall (9) traversed by at least one passage (11) having a central axis (C) and a valve (21) mounted in the passage (11), the valve (21) having a determined outer cross-section. The passage (11) has an inner end segment (23) that opens into the inner volume (7) and an outer end segment (25) that opens into an outer piping (13), the valve (21) being housed in the inner end segment (23). The valve (21) is capable of being extracted from the passage (11) through the inside of the vessel (1). The outer end segment (25) has at least one portion having an inner cross-section, perpendicular to the central axis (C), that is smaller than the outer cross-section of the valve (21), such that the valve (21) cannot be ejected out of the vessel (1).