Disclosed are fuel assemblies that are loaded in the core of a fast reactor including first fuel assemblies and second fuel assemblies being different from the first fuel assemblies. The reactor core has an axially heterogeneous core structure in which an internal blanket region containing depleted uranium fuel is placed around an axially middle section of the core. The first fuel assemblies are loaded in an outer core fuel region extending toward the periphery of the reactor core in a radial direction and the second fuel assemblies are loaded in an inner core fuel region extending around the center of the reactor core in a radial direction. Thickness of an internal blanket in each of the first fuel assemblies in an axial direction of the reactor core is thicker than thickness of an internal blanket in each of the second fuel assemblies in the axial direction of the reactor core.

A molten salt nuclear reactor of the fast neutron reactor type may be designed as a reactor vessel free of moderator or at the very least of a moderator enabling a reactor to be qualified as a thermal neutron reactor, having a shape exhibiting symmetry of revolution surrounded by another vessel at the periphery of the reactor vessel thereby delimiting a guard gap filled with an inert liquid salt which acts as a coolant for removing the decay heat from the reactor by conduction through the reactor vessel.

A fast neutron nuclear reactor contains a nuclear reactor core having an array of device locations. Some device locations in the nuclear reactor core contain fissile and fertile nuclear fuel assembly devices. One or more other device locations in the nuclear reactor core contain Doppler reactivity augmentation devices that amplify the negativity of the Doppler reactivity coefficient within the nuclear reactor core. In some implementations, a Doppler reactivity augmentation device can also reduce the coolant temperature coefficient within the nuclear reactor core. Accordingly, a Doppler reactivity augmentation device contributes to a more stable nuclear reactor core.

A traveling wave nuclear fission reactor, fuel assembly, and a method of controlling burnup therein. In a traveling wave nuclear fission reactor, a nuclear fission reactor fuel assembly comprises a plurality of nuclear fission fuel rods that are exposed to a deflagration wave burnfront that, in turn, travels through the fuel rods. The excess reactivity is controlled by a plurality of movable neutron absorber structures that are selectively inserted into and withdrawn from the fuel assembly in order to control the excess reactivity and thus the location, speed and shape of the burnfront. Controlling location, speed and shape of the burnfront manages neutron fluence seen by fuel assembly structural materials in order to reduce risk of temperature and irradiation damage to the structural materials.

An assembly to be inserted into a nuclear reactor, such as a liquid sodium-cooled fast neutron reactor SFR, includes an assembly hollow body, of elongate shape along a longitudinal axis X. The wall of the hollow body includes at least one open-ended opening. The assembly also includes an assembly element inserted at least in part into the hollow body. The assembly element includes at least one flexible blade of which the free end is shaped into a clip-fastening hook collaborating in clip-fastening with the open-ended opening from inside the hollow body, so as to connect the assembly element to the hollow body. The assembly also includes at least one removable structure for locking the flexible blade clip-fastened into the open-ended opening. The removable locking structure makes it possible to prevent the flexible blade from flexing and thus lock the connection between the assembly element and the hollow body.

Disclosed embodiments include nuclear fission reactors, nuclear fission fuel pins, methods of operating a nuclear fission reactor, methods of fueling a nuclear fission reactor, and methods of fabricating a nuclear fission fuel pin.

The invention relates to nuclear technology and may be used in preparing fuel rods and fuel assemblies for the cores of fast-neutron reactors utilizing a liquid-metal coolant. The invention reduces metal content of a fuel rod the contact stresses occurring in a fuel rod casing in a reactor core during nuclear fuel burnup. The fast neutron reactor fuel rod includes nuclear fuel disposed in a hermetically-sealed container in the form of a thin-walled tubular casing, and a spacing element wound in a wide-pitch spiral and secured to the casing or to the end components. The spacing element is a thin-walled tube having a longitudinal through-slot along the length thereof. Alternatively, the spacing element is made of a thin-walled tube or a thin band having a middle portion in the form of a tube with a longitudinal through-slot of a set width, and end components of fragments of the cylindrical casing.

The invention relates to the field of nuclear energy, more particularly to low-power and particularly low-power reactors. A nuclear reactor contains a housing with a reflector which forms a reactor core. The core has arranged therein primary process tubes, which are intended for circulating a coolant, and secondary process tubes, which are intended for accommodating elements of a control and protection system. The reactor also contains an intake chamber for coolant of a primary loop, and a discharge chamber for coolant of the primary loop, which are separated by a partition. The primary process tubes are designed in the form of Field tubes, the outer tubes of which are secured on the bottom of the intake chamber for the coolant of the primary loop, and the inner tubes are secured on the partition. Fuel assemblies are mounted in the inner tubes of the Field tubes on suspensions, which are secured on an upper portion of the discharge chamber for the coolant of the primary loop. The secondary process tubes are sealed off from the intake and discharge chambers for the coolant of the primary loop, and the inter-tube space of the core is filled with a medium or material which is transparent to neutrons.

A Single Fluid Reactor with an inner zone that includes a solid neutron moderator, which can have through holes defined therein. This solid neutron moderator can have a relatively small diameter, which can range, in some embodiments, from less than one meter to about 1.5 meter. The solid neutron moderator effectively creates an inner zone with a neutron profile that is far more thermalized than if the solid neutron moderator were absent. The surrounding layer of salt surrounding this inner zone has a much harder neutron spectrum.

An active zone includes a homogeneous uranium-plutonium nitride fuel, the mass fraction of which is a minimum 0.305, and consists of central, intermediate and peripheral parts which form fuel assemblies comprising fuel elements with geometrically identical shells but differing heights. The radial distribution of the fuel across the volume of the active zone has a stepped shape. The radius of the central part is from 0.4 to 0.5 of the effective active zone radius, while the height of the fuel column in the fuel elements in the central part is from 0.5 to 0.8 of the height of the fuel column in the peripheral part. The heights of the fuel columns forming a stepped intermediate part for diameters ranging from 0.5 to 0.85 of the effective active zone diameter are within the range from 0.55 to 0.9 of the height of the fuel column in the peripheral part.