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.

A nuclear reactor core includes a plurality of fuel elements and a skewed-pin moderator block array of skewed-pin moderator blocks to form a nuclear reactor core inner portion and a nuclear reactor core outer portion. The nuclear reactor core inner portion includes an inner moderator matrix formed of a plurality of inner holes that include a plurality of inner fuel openings with one or more fuel elements disposed therein. The plurality of inner holes further include a plurality of inner coolant passages to flow a coolant. The nuclear reactor core outer portion includes an outer moderator matrix formed of a plurality of outer holes that include a plurality of outer fuel openings with one or more fuel elements disposed therein. The plurality of outer holes further include a plurality of outer coolant passages to flow the coolant. The inner holes are irregularly spaced with respect to the outer holes.

A nuclear reactor core includes a plurality of fuel elements and a skewed-pin moderator block array of skewed-pin moderator blocks to form a nuclear reactor core inner portion and a nuclear reactor core outer portion. The nuclear reactor core inner portion includes an inner moderator matrix formed of a plurality of inner holes that include a plurality of inner fuel openings with one or more fuel elements disposed therein. The plurality of inner holes further include a plurality of inner coolant passages to flow a coolant. The nuclear reactor core outer portion includes an outer moderator matrix formed of a plurality of outer holes that include a plurality of outer fuel openings with one or more fuel elements disposed therein. The plurality of outer holes further include a plurality of outer coolant passages to flow the coolant. The inner holes are irregularly spaced with respect to the outer holes.

Combined moderator-propellant technologies allow a dual-purpose fluid to act as both a nuclear moderator as well as a propellant in a nuclear reactor system, such as a nuclear thermal propulsion (NTP) system. By increasing the mass efficiency of the NTP system and improving the overall performance during operation, the combined moderator-propellant technologies improve valuable payload efficiency in the NTP system. Advantageously, the combined moderator-propellant technologies require little to no dedicated storage space for the majority of NTP system operation. For example, the combined moderator-propellant is ammonia (NH.sub.3), which satisfies moderation requirements as well as propulsion requirements for the NTP system.

A closed-vessel molten salt reactor (cvMSR) is described herein. A cvMSR may comprise a suspended container, such as a metallic container, within a trench surrounded by a concrete enclosure and a concrete cover having a number of channels. The suspended container may be hollow and a solution of fissile materials and salt materials may be provided within the suspended container. The solution may be capable of undergoing a chain reaction nuclear fission process once a threshold temperature is reached. Heat generated by the solution may heat a fluid surrounding the suspended container. The heated fluid may be transported, through the number of channels of the concrete cover, to an external location where the heated fluid may be used in distributing heat and/or electricity generation.

A closed-vessel molten salt reactor (cvMSR) is described herein. A cvMSR may comprise a suspended container, such as a metallic container, within a trench surrounded by a concrete enclosure and a concrete cover having a number of channels. The suspended container may be hollow and a solution of fissile materials and salt materials may be provided within the suspended container. The solution may be capable of undergoing a chain reaction nuclear fission process once a threshold temperature is reached. Heat generated by the solution may heat a fluid surrounding the suspended container. The heated fluid may be transported, through the number of channels of the concrete cover, to an external location where the heated fluid may be used in distributing heat and/or electricity generation.

Power conversion systems for converting thermal energy from a heat source to electricity are disclosed. In one exemplary embodiment, the power conversion system may include a substantially sealed chamber having an inner shroud having an inlet and an outlet and defining an internal passageway between the inlet and the outlet through which a working fluid passes. The sealed chamber may also include an outer shroud substantially surrounding the inner shroud, such that the working fluid exiting the outlet of the inner shroud returns to the inlet of the inner shroud in a closed-loop via a return passageway formed between an external surface of the inner shroud and an internal surface of the outer shroud. The power conversion system may further include a source heat exchanger disposed in the internal passageway of the inner shroud, the source heat exchanger being configured to at least partially receive a heat transmitting element.

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 multipurpose small modular fluoride-salt-cooled high-temperature reactor energy system includes: a reactor body system, a passive residual heat removal system, a compact supercritical carbon dioxide Brayton cycle system, a secondary loop system, and a comprehensive utilization supercritical carbon dioxide Brayton cycle system. Nuclear reactor adopts helical cruciform fuel and graphite matrix material filled with TRISO element, which can improve heat transfer performance and inherent safety. Thermal efficiency of the compact supercritical carbon dioxide Brayton cycle system is above 48%, which can be used in places with limited space. Thermal efficiency of the comprehensive utilization supercritical carbon dioxide Brayton cycle system is above 54%, which can be applied to places with abundant resources. The present invention not only realizes efficient and compact utilization of energy, but also meets the needs of multiple purposes, integrated production, storage and conversion of energy.

A multipurpose small modular fluoride-salt-cooled high-temperature reactor energy system includes: a reactor body system, a passive residual heat removal system, a compact supercritical carbon dioxide Brayton cycle system, a secondary loop system, and a comprehensive utilization supercritical carbon dioxide Brayton cycle system. Nuclear reactor adopts helical cruciform fuel and graphite matrix material filled with TRISO element, which can improve heat transfer performance and inherent safety. Thermal efficiency of the compact supercritical carbon dioxide Brayton cycle system is above 48%, which can be used in places with limited space. Thermal efficiency of the comprehensive utilization supercritical carbon dioxide Brayton cycle system is above 54%, which can be applied to places with abundant resources. The present invention not only realizes efficient and compact utilization of energy, but also meets the needs of multiple purposes, integrated production, storage and conversion of energy.