Illustrative embodiments provide nuclear fission fuel elements, and systems, applications, apparatuses, and methods related thereto. Illustrative embodiments and aspects include, without limitation, nuclear fission fuel elements, heat pipe assemblies, heat pipes, methods of fabricating a nuclear fission fuel element, methods of fabricating a heat pipe assembly, and the like.

Passive reactivity control technologies that enable reactivity control of a nuclear thermal propulsion (NTP) system with little to no active mechanical movement of circumferential control drums. By minimizing or eliminating the need for mechanical movement of the circumferential control drums during an NTP burn, the reactivity control technologies simplify controlling an NTP reactor and increase the overall performance of the NTP system. The reactivity control technologies mitigate and counteract the effects of xenon, the dominant fission product contributing to reactivity transients. Examples of reactivity control technologies include, employing burnable neutron poisons, tuning hydrogen pressure, adjusting wait time between burn cycles or merging burn cycles, and enhancement of temperature feedback mechanisms. The reactivity control technologies are applicable to low-enriched uranium NTP systems, including graphite composite fueled and tungsten ceramic and metal matrix (CERMET), or any moderated NTP system, such as highly-enriched uranium graphite composite NTP systems.

The disclosure relates to a high temperature gas-cooled reactor core including a plurality of elongate fuel elements arranged in the form of a multi-lobed prism. Each prismatic fuel element includes an elongate prismatic body and a plurality of elongate fuel channels located within the prismatic body, wherein the cross-sectional area of each prismatic fuel element in a plane parallel to the bases of the prismatic fuel element is no more than 800 cm.sup.2 and wherein a ratio of the height of the prismatic body to its greatest width is greater than or equal to 3.0.

The disclosure relates to a high temperature gas-cooled reactor core including a plurality of elongate fuel elements arranged in the form of a multi-lobed prism. Each prismatic fuel element includes an elongate prismatic body and a plurality of elongate fuel channels located within the prismatic body, wherein the cross-sectional area of each prismatic fuel element in a plane parallel to the bases of the prismatic fuel element is no more than 800 cm.sup.2 and wherein a ratio of the height of the prismatic body to its greatest width is greater than or equal to 3.0.

A nuclear reactor (10) includes a vessel (12) containing a primary liquid, a core (14) comprising nuclear fuel and arranged in the internal volume of the vessel (12), at least one primary pump generating a main primary flow (56) of primary liquid in the vessel (12), at least one control member (16) for controlling the reactivity of the core (14), at least one movement mechanism (18) for moving the control member (16), arranged in the internal volume of the vessel (12) and linked to the control member (16), and a pressurizer (20) situated in a top portion of the vessel (12). The movement mechanism (18) comprises an electrical actuator and a transmission mechanism. The electrical actuator is completely immersed in the primary fluid and situated outside the main primary flow (56).

A nuclear reactor (10) includes a vessel (12) containing a primary liquid, a core (14) comprising nuclear fuel and arranged in the internal volume of the vessel (12), at least one primary pump generating a main primary flow (56) of primary liquid in the vessel (12), at least one control member (16) for controlling the reactivity of the core (14), at least one movement mechanism (18) for moving the control member (16), arranged in the internal volume of the vessel (12) and linked to the control member (16), and a pressurizer (20) situated in a top portion of the vessel (12). The movement mechanism (18) comprises an electrical actuator and a transmission mechanism. The electrical actuator is completely immersed in the primary fluid and situated outside the main primary flow (56).

The disclosure relates to a high temperature gas-cooled reactor core including a plurality of elongate fuel elements arranged in the form of a multi-lobed prism. Each prismatic fuel element includes an elongate prismatic body and a plurality of elongate fuel channels located within the prismatic body, wherein the cross-sectional area of each prismatic fuel element in a plane parallel to the bases of the prismatic fuel element is no more than 800 cm.sup.2 and wherein a ratio of the height of the prismatic body to its greatest width is greater than or equal to 3.0.

The disclosure relates to a high temperature gas-cooled reactor core including a plurality of elongate fuel elements arranged in the form of a multi-lobed prism. Each prismatic fuel element includes an elongate prismatic body and a plurality of elongate fuel channels located within the prismatic body, wherein the cross-sectional area of each prismatic fuel element in a plane parallel to the bases of the prismatic fuel element is no more than 800 cm.sup.2 and wherein a ratio of the height of the prismatic body to its greatest width is greater than or equal to 3.0.

A fuel assembly for a pressure-tube nuclear reactor includes a fuel channel assembly. The fuel channel assembly has an outer conduit and an inner conduit received within the outer conduit. The conduits define an annular fuel bundle chamber for receiving a flow of a coolant in one direction. The inner conduit includes a central flow passage for receiving a flow of the coolant in an opposite direction. A fuel bundle positioned within the fuel bundle chamber consists of fuel elements arranged to form an inner ring surrounding the inner conduit, and an outer ring surrounding the inner ring. The coolant may be light water, and geometries of the fuel assembly may be selected so moderation by the volume of coolant promotes generally uniform power distribution in the fuel elements.

A fuel assembly for a pressure-tube nuclear reactor includes a fuel channel assembly. The fuel channel assembly has an outer conduit and an inner conduit received within the outer conduit. The conduits define an annular fuel bundle chamber for receiving a flow of a coolant in one direction. The inner conduit includes a central flow passage for receiving a flow of the coolant in an opposite direction. A fuel bundle positioned within the fuel bundle chamber consists of fuel elements arranged to form an inner ring surrounding the inner conduit, and an outer ring surrounding the inner ring. The coolant may be light water, and geometries of the fuel assembly may be selected so moderation by the volume of coolant promotes generally uniform power distribution in the fuel elements.