In one embodiment, the fuel bundle for a liquid metal cooled reactor includes a channel, a nose assembly secured to a lower end of the channel, and a plurality of fuel rods disposed within the channel. At least one of the fuel rods has at least one guard ring surround the fuel rod and spacing the fuel rod from adjacent fuel rods.

In one embodiment, the fuel bundle for a liquid metal cooled reactor includes a channel, a nose assembly secured to a lower end of the channel, and a plurality of fuel rods disposed within the channel. At least one of the fuel rods has at least one guard ring surround the fuel rod and spacing the fuel rod from adjacent fuel rods.

In one embodiment, the fuel bundle for a liquid metal cooled reactor includes a channel, a nose assembly secured to a lower end of the channel, and a plurality of fuel rods disposed within the channel. At least one of the fuel rods has at least one guard ring surround the fuel rod and spacing the fuel rod from adjacent fuel rods.

In one embodiment, the fuel bundle for a liquid metal cooled reactor includes a channel, a nose assembly secured to a lower end of the channel, and a plurality of fuel rods disposed within the channel. At least one of the fuel rods has at least one guard ring surround the fuel rod and spacing the fuel rod from adjacent fuel rods.

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 fuel assembly includes a base material formed of a zirconium alloy and a coating layer, and the coating layer includes a chromium layer formed of chromium or a chromium alloy and a corrosion-resistant layer formed of zirconium alloy or a titanium alloy. The method for producing a fuel assembly includes a step of preparing the base material, a step of forming the chromium layer on a surface of the base material that would otherwise be in contact with cooling water, a step of forming the corrosion-resistant layer on a surface of the chromium layer, and a step of assembling the fuel assembly using the base material. The chromium layer and the corrosion-resistant layer are formed according to a thin plate cladding method, a physical vapor deposition method, a thermal spraying method, a cold spraying method, or a plating method before the assembling using the base material.

The fuel assembly includes a base material formed of a zirconium alloy and a coating layer, and the coating layer includes a chromium layer formed of chromium or a chromium alloy and a corrosion-resistant layer formed of zirconium alloy or a titanium alloy. The method for producing a fuel assembly includes a step of preparing the base material, a step of forming the chromium layer on a surface of the base material that would otherwise be in contact with cooling water, a step of forming the corrosion-resistant layer on a surface of the chromium layer, and a step of assembling the fuel assembly using the base material. The chromium layer and the corrosion-resistant layer are formed according to a thin plate cladding method, a physical vapor deposition method, a thermal spraying method, a cold spraying method, or a plating method before the assembling using the base material.