A variable diameter fuel rod of a nuclear reactor assembly is disclosed. The variable diameter fuel rod includes an elongated cladding tube configured to house a plurality of fuel pellets including a fissile material arranged in a fuel stack orientation. The elongated cladding tube includes first and second axial reflector regions and a middle axial region therebetween. The middle axial region comprises an outer diameter defined as d.sub.1. The first and second axial reflector regions include an outer cladding diameter defined as d.sub.2 and d.sub.3, respectively. The variable diameter fuel rod further includes a transitional region between the diameter d.sub.1 of the middle axial region and the diameter d.sub.2 of the axial reflector region. The diameter d.sub.2 of the axial reflector region is greater than the diameter d.sub.1 of the middle axial region.

Hydrogen-resistant coatings and associated systems and methods are generally described. In some aspects, a hydrogen-resistant coating comprises a doped tin oxide comprising one or more dopants. The doped tin oxide may, in some cases, exhibit low hydrogen solubility and low hydrogen diffusivity and may therefore reduce and/or prevent permeation of hydrogen in an underlying substrate. In some embodiments, the one or more dopants comprise one or more transition metals (e.g., tungsten, molybdenum, niobium).

A nuclear-fuel pin including a linear element made of a metal nuclear-fuel material consisting of uranium and/or plutonium, and cladding including Fe and Cr or an alloy including at least both of said elements, comprises a main shell provided around the linear nuclear-fuel element, said shell including threads or fibers made of SiC. A method for producing a nuclear-fuel pin is also provided.

Provided herein is a fuel rod and a fuel assembly for light water reactors in which crack penetration to a fuel cladding tube or an end plug can be prevented even when cracking occurs at the joint between the fuel cladding tube and the end plug for which a ceramic base material is used. A fuel rod 10a for light water reactors includes: a cylindrical cladding tube 11 formed of a ceramic base material; a connection 21 formed of the same or similar material to the cladding tube 11; and an end plug 12a having a concave portion 12f of a continuously curved surface shape adapted to house the connection 21. The end plug 12a is formed of the same or similar material to the cladding tube 11. A slanted surface 11a formed at an end portion of the cladding tube 11, and a slanted surface 12d formed at an end portion of the end plug 12a are joined in contact with each other with a metallic joint material 20. The joint is supported by the connection 21.

The invention relates to a nuclear fuel cladding comprising: i) a substrate containing a zirconium-based inner layer, optionally coated with at least one intermediate layer formed by at least one intermediate material selected from among tantalum, molybdenum, tungsten, niobium, vanadium, hafnium or the alloys thereof; and ii) at least one protective outer layer placed on the substrate and formed by a protective material selected from either chromium or an alloy of chromium. The nuclear fuel cladding produced using the method of the invention has improved resistance to oxidation/hydriding. The invention also relates to the method for the production of the nuclear fuel cladding by ion etching of the surface of the substrate and deposition of the outer layer on the substrate with a high power impulse magnetron sputtering method (HiPIMS), as well as to the use thereof to protect against oxidation and/or hydriding.

The method includes assessing operational characteristics of the fuel assembly, the assessing including determining if the fuel assembly is to be placed in a controlled location in the reactor core, a controlled location being positioned adjacent to a control blade that is to be utilized, and configuring the sidewalls of the outer channel by making at least a first select sidewall of the outer channel a reinforced sidewall, the remaining sidewalls of the outer channel, other than the at least a first select sidewall, being non-reinforced sidewalls. The entirety of the reinforced sidewall as a whole is at least one of thicker and made from a material that is more resistant to radiation-induced deformation as compared to an entirety of the non-reinforced sidewalls.

The method includes assessing operational characteristics of the fuel assembly, the assessing including determining if the fuel assembly is to be placed in a controlled location in the reactor core, a controlled location being positioned adjacent to a control blade that is to be utilized, and configuring the sidewalls of the outer channel by making at least a first select sidewall of the outer channel a reinforced sidewall, the remaining sidewalls of the outer channel, other than the at least a first select sidewall, being non-reinforced sidewalls. The entirety of the reinforced sidewall as a whole is at least one of thicker and made from a material that is more resistant to radiation-induced deformation as compared to an entirety of the non-reinforced sidewalls.

Nuclear fuel assemblies include non-symmetrical fuel elements with reduced lateral dimensions on their outer lateral sides that facilitate fitting the fuel assembly into the predefined envelope size and guide tube position and pattern of a conventional nuclear reactor. Nuclear fuel assemblies alternatively comprise a mixed grid pattern that positions generally similar fuel elements in a compact arrangement that facilitates fitting of the assembly into the conventional nuclear reactor.

Nuclear fuel assemblies include non-symmetrical fuel elements with reduced lateral dimensions on their outer lateral sides that facilitate fitting the fuel assembly into the predefined envelope size and guide tube position and pattern of a conventional nuclear reactor. Nuclear fuel assemblies alternatively comprise a mixed grid pattern that positions generally similar fuel elements in a compact arrangement that facilitates fitting of the assembly into the conventional nuclear reactor.

Nuclear fuel assemblies include fuel elements that are sintered or cast into billets and co-extruded into a spiral, multi-lobed shape. The fuel kernel may be a metal alloy of metal fuel material and a metal-non-fuel material, or ceramic fuel in a metal non-fuel matrix. The fuel elements may use more highly enriched fissile material while maintaining safe operating temperatures. Such fuel elements according to one or more embodiments may provide more power at a safer, lower temperature than possible with conventional uranium oxide fuel rods. The fuel assembly may also include a plurality of conventional UO2 fuel rods, which may help the fuel assembly to conform to the space requirements of conventional nuclear reactors.