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, are provided. The fuel rod 10a includes: a cylindrical cladding tube 11 formed of a ceramic base material; a connection 21 formed of the same material as 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 material as 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.

Nuclear propulsion fission reactor structure has an active core region including fuel element structures, a reflector with rotatable neutron absorber structures (such as drum absorbers), and a core former conformal mating the outer surface of the fuel element structures to the reflector. Fuel element structures are arranged abutting nearest neighbor fuel element structures in a tri-pitch design. Cladding bodies defining coolant channels are inserted into and joined to lower and upper core plates to from a continuous structure that is a first portion of the containment structure. The body of the fuel element has a structure with a shape corresponding to a mathematically-based periodic solid, such as a triply periodic minimal surface (TPMS) in a gyroid structure. The nuclear propulsion fission reactor structure can be incorporated into a nuclear thermal propulsion engine for propulsion applications, such as space propulsion.

Nuclear propulsion fission reactor structure has an active core region including fuel element structures, a reflector with rotatable neutron absorber structures (such as drum absorbers), and a core former conformal mating the outer surface of the fuel element structures to the reflector. Fuel element structures are arranged abutting nearest neighbor fuel element structures in a tri-pitch design. Cladding bodies defining coolant channels are inserted into and joined to lower and upper core plates to from a continuous structure that is a first portion of the containment structure. The body of the fuel element has a structure with a shape corresponding to a mathematically-based periodic solid, such as a triply periodic minimal surface (TPMS) in a gyroid structure. The nuclear propulsion fission reactor structure can be incorporated into a nuclear thermal propulsion engine for propulsion applications, such as space propulsion.

A nuclear fuel assembly having lateral support provided by a bimetallic spring that extends from a side of the fuel assembly under certain core conditions to pressure against an adjacent component and withdraws under other core conditions, such as shutdown, to enable the nuclear fuel assembly to be aligned or withdrawn from the core and repositioned.

A fuel element has a ratio of area of fissionable nuclear fuel in a cross-section of the tubular fuel element perpendicular to the longitudinal axis to total area of the interior volume in the cross-section of the tubular fuel element that varies with position along the longitudinal axis. The ratio can vary with position along the longitudinal axis between a minimum of 0.30 and a maximum of 1.0. Increasing the ratio above and below the peak burn-up location associated with conventional systems reduces the peak burn-up and flattens and shifts the burn-up distribution, which is preferably Gaussian. The longitudinal variation can be implemented in fuel assemblies using fuel bodies, such as pellets, rods or annuli, or fuel in the form of metal sponge and meaningfully increases efficiency of fuel utilization.

A fuel element has a ratio of area of fissionable nuclear fuel in a cross-section of the tubular fuel element perpendicular to the longitudinal axis to total area of the interior volume in the cross-section of the tubular fuel element that varies with position along the longitudinal axis. The ratio can vary with position along the longitudinal axis between a minimum of 0.30 and a maximum of 1.0. Increasing the ratio above and below the peak burn-up location associated with conventional systems reduces the peak burn-up and flattens and shifts the burn-up distribution, which is preferably Gaussian. The longitudinal variation can be implemented in fuel assemblies using fuel bodies, such as pellets, rods or annuli, or fuel in the form of metal sponge and meaningfully increases efficiency of fuel utilization.

A fuel channel for a nuclear power boiling water reactor is configured to include a bundle of fuel rods with nuclear fuel. The fuel channel is made of a sheet material and has a plurality of sides which have an elongated shape and which are connected to each other such that a corner with an elongated shape is formed where two adjacent sides meet. In one or more corners, the sheet materials from the two adjacent sides overlap with each other such that there is a corner region with double sheet material consisting of the overlapping sheet material from one of the two sides and the overlapping sheet material from the other of the two sides.

A fuel channel for a nuclear power boiling water reactor is configured to include a bundle of fuel rods with nuclear fuel. The fuel channel is made of a sheet material and has a plurality of sides which have an elongated shape and which are connected to each other such that a corner with an elongated shape is formed where two adjacent sides meet. In one or more corners, the sheet materials from the two adjacent sides overlap with each other such that there is a corner region with double sheet material consisting of the overlapping sheet material from one of the two sides and the overlapping sheet material from the other of the two sides.

The present invention relates generally to electric power and process heat generation using a modular, compact, transportable, hardened nuclear generator rapidly deployable and retrievable, comprising power conversion and electric generation equipment fully integrated within a single pressure vessel housing a nuclear core. The resulting transportable nuclear generator does not require costly site-preparation, and can be transported fully operational. The transportable nuclear generator requires an emergency evacuation area substantially reduced with respect to other nuclear generators as it may be configured for operation with a melt-proof conductive ceramic core which allows decay heat removal even under total loss of coolant scenarios.

The main purpose of the invention is a mitigation assembly (40) for a nuclear reactor comprising a box (41) with an upper portion (41) forming the head of the assembly housing an upper neutron shielding (UNS) device, comprising a head (105) comprising removable locking means (100) and a slug (101) installed free to move in translation relative over a given travel distance, the locking means (100) being configured such that locking/unlocking between the head (105) and the box (41) can be made by displacement of the slug (101) by means of an extraction grab with its pawls attached in the slug (101), characterised in that the lower part of the upper neutron shielding device comprises a cone-shaped sealing block (107) with the tip of the cone oriented downwards, cooperating with a cone-shaped internal surface (108) of the box (41), a sealing device (109) being formed between the two, the assembly created forming a removable sealing plug (110).