The present disclosure is generally related to methods, devices and systems for improving the performances of a Rod Cluster Control Assembly (RCCA) and/or a Control Element Assembly (CEA) to mitigate clad strain, especially in the high fluence region, during normal operation conditions and accident conditions. One method may include incorporating a device such as a powder collection and blockage device between the ceramic upper and ceramic lower absorber materials of the RCCA and/or CEA. Another method may include increasing the plenum volume by incorporating an axial hole into the top end plug extension. Another method may include increasing the plenum volume by incorporating an axial hole into the bottom end plug and optionally incorporating radial grooves in the bottom of the lower absorber material to provide a flow channel for gas expansion or generation to ensure that the lower absorber does not block the opening in the bottom end plug.

The present disclosure is generally related to methods, devices and systems for improving the performances of a Rod Cluster Control Assembly (RCCA) and/or a Control Element Assembly (CEA) to mitigate clad strain, especially in the high fluence region, during normal operation conditions and accident conditions. One method may include incorporating a device such as a powder collection and blockage device between the ceramic upper and ceramic lower absorber materials of the RCCA and/or CEA. Another method may include increasing the plenum volume by incorporating an axial hole into the top end plug extension. Another method may include increasing the plenum volume by incorporating an axial hole into the bottom end plug and optionally incorporating radial grooves in the bottom of the lower absorber material to provide a flow channel for gas expansion or generation to ensure that the lower absorber does not block the opening in the bottom end plug.

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.

A fuel assembly for a boiling water reactor, having fuel rods, a tie plate, a handle device, and at least two water rods attached to the tie plate and to the handle device. A plurality of spacers, define first passages for some of the fuel rods, and second passages for the water rods. Each water rod comprises a tube part attached to the tie plate, and a solid part attached to the handle device. The tube part permits a flow of coolant. The spacers include primary spacers and a secondary spacer. The primary spacers are attached to the tube parts. The tie plate, the water rods, the primary spacers and the handle device form a support structure carrying the weight of the fuel rods. The secondary spacer is positioned at the solid part of the respective water rod.

Systems and methods for providing and using molten salt reactors are described. While the systems can include any suitable component, in some cases, they include a graphite reactor core defining an internal space that houses one or more fuel wedges, where each wedge defines one or more fuel channels that extend from a first end to a second end of the wedge. In some cases, one or more of the fuel wedges comprise multiple wedge sections that are coupled together end to end and/or in any other suitable manner. In some cases, one or more alignment pins also extend between two sections of a fuel wedge to align the sections. In some cases, one or more seals are also disposed between two sections of a fuel wedge. Thus, in some cases, the reactor core can be relatively long (e.g., to be a pipeline reactor). Other implementations are also described.

Systems and methods for providing and using molten salt reactors are described. While the systems can include any suitable component, in some cases, they include a graphite reactor core defining an internal space that houses one or more fuel wedges, where each wedge defines one or more fuel channels that extend from a first end to a second end of the wedge. In some cases, one or more of the fuel wedges comprise multiple wedge sections that are coupled together end to end and/or in any other suitable manner. In some cases, one or more alignment pins also extend between two sections of a fuel wedge to align the sections. In some cases, one or more seals are also disposed between two sections of a fuel wedge. Thus, in some cases, the reactor core can be relatively long (e.g., to be a pipeline reactor). Other implementations are also described.

A new, improved grid spacer for a nuclear fuel assembly is provided, comprising several straps which intersect each other alternatively to form a plurality of grid cells and fuel rods reside in some of the grid cells; the grid spacer further comprises mixing elements set at the corner of the grid cells in which the fuel rods have resided; wherein the mixing element comprises a mixing vane stretching towards the direction of the fuel rod and a flow funnel set on the bended edge of the mixing vane continuously and extending towards adjacent grid cells; the mixing vane and the flow funnel set across two sides of two adjacent grid cells respectively, and the flow funnel introduces the coolant in the grid cell at its side to the mixing vane, then the mixing vane introduces the coolant to the grid cell at its own side.

A new, improved grid spacer for a nuclear fuel assembly is provided, comprising several straps which intersect each other alternatively to form a plurality of grid cells and fuel rods reside in some of the grid cells; the grid spacer further comprises mixing elements set at the corner of the grid cells in which the fuel rods have resided; wherein the mixing element comprises a mixing vane stretching towards the direction of the fuel rod and a flow funnel set on the bended edge of the mixing vane continuously and extending towards adjacent grid cells; the mixing vane and the flow funnel set across two sides of two adjacent grid cells respectively, and the flow funnel introduces the coolant in the grid cell at its side to the mixing vane, then the mixing vane introduces the coolant to the grid cell at its own side.

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.

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.