Nuclear reactor systems and associated devices and methods are described herein. A representative nuclear reactor system includes a reactor vessel having a barrier separating a core region from a shield region. A plurality of fuel rods containing a liquid nuclear fuel are positioned in the core region. A liquid moderator material is also positioned in the core region at least partially around the fuel rods. A plurality of heat exchangers can be positioned in the shield region, and a plurality of heat pipes can extend through the barrier. The moderator material is positioned to transfer heat received from the liquid nuclear fuel to the heat pipes, and the heat pipes are positioned to transfer heat received from the moderator material to the heat exchangers. The heat exchangers can transport the heat out of the system for use in one or more processes, such as generating electricity.

To reduce size and mass of a nuclear reactor system, an integrated in-vessel shield separates the role of a neutron reflector and a neutron shield. Nuclear reactor system includes a pressure vessel including an interior wall and a nuclear reactor core located within the interior wall of the pressure vessel. Nuclear reactor core includes a plurality of fuel elements and at least one moderator element. Nuclear reactor system includes a reflector located inside the pressure vessel that includes a plurality of reflector blocks laterally surrounding the plurality of fuel elements and the at least one moderator element. Nuclear reactor system includes the in-vessel shield located on the interior wall of the pressure vessel to surround the reflector blocks. In-vessel shield is formed of two or more neutron absorbing materials. The two more neutron absorbing materials include a near black neutron absorbing material and a gray neutron absorbing material.

A nuclear fuel element is provided. The nuclear fuel element includes a porous support. The porous support includes a ligament and defines a pore adjacent to the ligament. The ligament has an interior surface spaced from the pore. The interior surface defines a void. The porous support includes silicon carbide. The nuclear fuel element includes a nuclear fuel material disposed in the pore. The nuclear fuel material includes a moderator and tri-structural isotropic (TRISO) particles. Another nuclear fuel element is provided. The nuclear fuel element includes a porous support. The porous support includes a ligament and defines a pore adjacent to the ligament. The ligament has an interior surface spaced from the pore. The interior surface defines a void. The ligament includes the nuclear fuel material. The nuclear fuel element includes a facesheet overlying the porous support and defines a hole. The hole is in fluid communication with the void. The nuclear fuel material includes a nuclear fuel.

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. The fuel salt cooling system is configured such that during operation of the reactor, for all points within the fuel salt within each fuel tube except at the respective gas interface:

[00001]$T_2>\frac{1}{-\frac{R_{\mathrm{He}}}{\Delta H_{\mathrm{He}}}*\ln \left(\frac{P_1}{P_2}\right)+\frac{1}{T_1}}$

A modular, nuclear waste conversion reactor that continuously produces usable energy while converting U-238 and/or other fertile waste materials to fissionable nuclides. The reactor has a highly uniform, self-controlled, core (2) with a decades-long life and does not require reactivity control mechanisms within the boundary of the active core during operation to retain adequate safety. The exemplary embodiment employs high-temperature helium coolant, a dual-segment (22) initial annular critical core, carbide fuel, a fission product gas collection system, ceramic cladding and structural internals to create a modular reactor design that economically produces energy over multiple generations of reactor cores with only minimum addition of fertile material from one generation to the next.

Illustrative embodiments provide a nuclear fission reactor, that includes a reactor vessel, a nuclear fission fuel element capable of generating a gaseous fission product, a valve body defining a plenum for receiving the gaseous fission product, and a valve in operative communication with the plenum for controllably venting the gaseous fission product from the plenum.

An apparatus and method for pressurizing SiC clad rods of a nuclear core component. A lower end of the rod is sealed with a lower end plug and an upper end of the rod is sealed between the cladding and an external piece of an upper end plug that has a through opening through which a separate internal piece of the upper end plug extends. The internal piece of the upper end plug is initially moveable within the through opening between an upper position that forms a gas tight seal and a lower position that forms a gaseous path through the through opening. The rod is placed in a pressure chamber pressurized to a desired pressure. When the pressure is reduced within the pressure chamber the internal pressure in the rod biases the internal piece of the upper end plug in the upper sealed position.

A nuclear reactor system includes a nuclear reactor core disposed in a pressure vessel. Nuclear reactor system further includes control drums disposed longitudinally within the pressure vessel and laterally surrounding fuel elements and at least one moderator element of the nuclear reactor core to control reactivity. Each of the control drums includes a reflector material and an absorber material. Nuclear reactor system further includes an automatic shutdown controller and an electrical drive mechanism coupled to rotatably control the control drum. Automatic shutdown controller includes a counterweight to impart a bias and an actuator. To automatically shut down the nuclear reactor core during a loss or interruption of electrical power from a power source to the electrical drive mechanism, the actuator is coupled to the counterweight and responsive to the bias to align the absorber material of one or more control drums to face inwards towards the nuclear reactor core.

An enhanced architecture for a nuclear reactor core includes several technologies: (1) nuclear fuel tiles (S-Block); and (2) a high-temperature thermal insulator and tube liners with a low-temperature solid-phase moderator (U-Mod) to improve safety, reliability, heat transfer, efficiency, and compactness. In S-Block, nuclear fuel tiles include a fuel shape designed with an interlocking geometry pattern to optimize heat transfer between nuclear fuel tiles and into a fuel coolant and bring the fuel coolant in direct contact with the nuclear fuel tiles. Nuclear fuel tiles can be shaped with discontinuous nuclear fuel lateral facets and have fuel coolant passages formed therein to provide direct contact between the fuel coolant and the nuclear fuel tiles. In U-Mod, tube liners with low hydrogen diffusivity retain hydrogen in the low-temperature solid-phase moderator even at elevated temperatures and the high-temperature thermal insulator insulates the solid-phase moderator from the nuclear fuel tiles.

Provided is a nuclear-fuel sintered pellet based on oxide in which a plate-type fine precipitate material in a base of a sintered pellet of uranium dioxide, used as nuclear fuel in nuclear power plants, is uniformly dispersed in a matrix of uranium dioxide fuel thereof so as to form a donut-shaped precipitate cluster, and to a method of manufacturing the same. The plate-type fine precipitate material is uniformly precipitated in a tissue thereof or forms a donut-shaped precipitate cluster having a two-dimensional structure through dispersion to improve thermal and physical performance of the nuclear-fuel sintered pellet of uranium dioxide, whereby the creep deformation rate and thermal conductivity of the sintered pellet are improved. The nuclear-fuel sintered pellet based on oxide can reduce the Pellet-Clad Interaction (PCI) failure and the core temperature of nuclear fuel when an accident occurs, thereby significantly improving the safety of a nuclear reactor.