This disclosure describes nuclear fuel salts usable in certain molten salt reactor designs and related systems and methods. Binary, ternary and quaternary chloride fuel salts of uranium, as well as other fissionable elements, are described. In addition, fuel salts of UCl.sub.xF.sub.y are disclosed as well as bromide fuel salts. This disclosure also presents methods and systems for manufacturing such fuel salts, for creating salts that reduce corrosion of the reactor components and for creating fuel salts that are not suitable for weapons applications.

Illustrative embodiments provide a reactivity control assembly for a nuclear fission reactor, a reactivity control system for a nuclear fission reactor having a fast neutron spectrum, a nuclear fission traveling wave reactor having a fast neutron spectrum, a method of controlling reactivity in a nuclear fission reactor having a fast neutron spectrum, methods of operating a nuclear fission traveling wave reactor having a fast neutron spectrum, a system for controlling reactivity in a nuclear fission reactor having a fast neutron spectrum, a method of determining an application of a controllably movable rod, a system for determining an application of a controllably movable rod, and a computer program product for determining an application of a controllably movable rod.

Illustrative embodiments provide a reactivity control assembly for a nuclear fission reactor, a reactivity control system for a nuclear fission reactor having a fast neutron spectrum, a nuclear fission traveling wave reactor having a fast neutron spectrum, a method of controlling reactivity in a nuclear fission reactor having a fast neutron spectrum, methods of operating a nuclear fission traveling wave reactor having a fast neutron spectrum, a system for controlling reactivity in a nuclear fission reactor having a fast neutron spectrum, a method of determining an application of a controllably movable rod, a system for determining an application of a controllably movable rod, and a computer program product for determining an application of a controllably movable rod.

Illustrative embodiments provide methods and systems for migrating fuel assemblies in a nuclear fission reactor, methods of operating a nuclear fission traveling wave reactor, methods of controlling a nuclear fission traveling wave reactor, systems for controlling a nuclear fission traveling wave reactor, computer software program products for controlling a nuclear fission traveling wave reactor, and nuclear fission traveling wave reactors with systems for migrating fuel assemblies.

Illustrative embodiments provide methods and systems for migrating fuel assemblies in a nuclear fission reactor, methods of operating a nuclear fission traveling wave reactor, methods of controlling a nuclear fission traveling wave reactor, systems for controlling a nuclear fission traveling wave reactor, computer software program products for controlling a nuclear fission traveling wave reactor, and nuclear fission traveling wave reactors with systems for migrating fuel assemblies.

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.

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.

A nuclear fuel rod end distance adjusting device includes an insertion rod, a housing having a hollow space, insertion power means installed inside the housing, a connector connected between the insertion power means and the insertion rod, and an anti-rotation tool installed between the insertion power means and the connector. The insertion rod includes nuclear fuel rod tongs and configured to linearly move forward and backward. The insertion power means is configured to move in a longitudinal direction of the housing by converting a rotational motion into a linear motion. The anti-rotation tool is configured to move in the longitudinal direction of the housing by being interlocked with the linear motion of the insertion power means, but preventing rotational force of the insertion power means from being transmitted to the connector. Thereby, movement and end distance of the fuel rods can be more minutely and stably adjusted.

A nuclear reactor includes a passive reactivity control nuclear fuel device located in a nuclear reactor core. The passive reactivity control nuclear fuel device includes a multiple-walled fuel chamber having an outer wall chamber and an inner wall chamber contained within the outer wall chamber. The inner wall chamber is positioned within the outer wall chamber to hold nuclear fuel in a molten fuel state within a high neutron importance region. The inner wall chamber allows at least a portion of the nuclear fuel to move in a molten fuel state to a lower neutron importance region while the molten nuclear fuel remains within the inner wall chamber as the temperature of the nuclear fuel satisfies a negative reactivity feedback expansion temperature condition. A duct contains the multiple-walled fuel chamber and flows a heat conducting fluid through the duct and in thermal communication with the outer wall chamber.

A nuclear reactor includes a passive reactivity control nuclear fuel device located in a nuclear reactor core. The passive reactivity control nuclear fuel device includes a multiple-walled fuel chamber having an outer wall chamber and an inner wall chamber contained within the outer wall chamber. The inner wall chamber is positioned within the outer wall chamber to hold nuclear fuel in a molten fuel state within a high neutron importance region. The inner wall chamber allows at least a portion of the nuclear fuel to move in a molten fuel state to a lower neutron importance region while the molten nuclear fuel remains within the inner wall chamber as the temperature of the nuclear fuel satisfies a negative reactivity feedback expansion temperature condition. A duct contains the multiple-walled fuel chamber and flows a heat conducting fluid through the duct and in thermal communication with the outer wall chamber.