A method comprises inserting the fuel rod (4) through the spacer grids (14) aligned along an assembling axis (A) with passing the fuel rod (4) through a lubrication chamber (30) aligned with the spacer grids (14) such that the lubrication chamber (30) is passed through by the fuel rod (4) before the insertion of the fuel rod (4) through one of the spacer grids (14), and circulating a lubrication fluid containing a gas and a lubricant in gaseous phase and/or mist form in the lubrication chamber (30). The lubrication fluid is injected in the lubrication chamber (30) at a temperature strictly higher than ambient temperature, such that lubricant deposits or condensates in liquid phase with forming a lubricant film on an external surface of the fuel rod (4) that is being inserted through said one of the spacer grids (14).

Provided is a structure including a first member (2); a second member (3) disposed opposite to the first member (2); and a glass layer (4) disposed between the first member (2) and the second member (3) so as to bond the first member (2) and the second member (3). A glass transition point of the glass layer (4) is lower than a temperature of the glass layer (4) under operation. In the glass layer (4), at least either of ceramic and metallic particles 4b, 4c is dispersed. In a temperature region lower than the glass transition point of the glass layer (4), a thermal expansion coefficient thereof falls in between thermal expansion coefficients of the first member (2) and the second member (3). This allows thermal strain caused within the structure (1) to be reduced when the structure (1) is operated at a higher temperature than a room temperature.

Provided is a structure including a first member (2); a second member (3) disposed opposite to the first member (2); and a glass layer (4) disposed between the first member (2) and the second member (3) so as to bond the first member (2) and the second member (3). A glass transition point of the glass layer (4) is lower than a temperature of the glass layer (4) under operation. In the glass layer (4), at least either of ceramic and metallic particles 4b, 4c is dispersed. In a temperature region lower than the glass transition point of the glass layer (4), a thermal expansion coefficient thereof falls in between thermal expansion coefficients of the first member (2) and the second member (3). This allows thermal strain caused within the structure (1) to be reduced when the structure (1) is operated at a higher temperature than a room temperature.

A holding fixture for assisting in assembly of a support grid for nuclear fuel rods and including a plurality of straps each having a plurality of slots extending approximately half a height of the straps and tabs formed beside or between the slots. The holding fixture includes an actuation plate, a support plate having a plurality of receiving members structured to receive therein straps of the support grid and having a plurality of cells, and a plurality of cam assemblies structured to move to deflect every other tab of the straps received in the plurality of receiving members. The cam assemblies are disposed in every other cell of the support plate.

A heat exchanger devices for operations in heavy liquid metal coolant mediums that ensures reliable fixation and spacing of heat exchanger tubes. A first option includes one supporting spacer grid 1 consisting of a cylindrical shell 2 and two or more tiers of plates 3 and 4 spaced apart at the preset gap, while the width of each plate lies within the plane which is parallel to the shell axis; ends of all plates are fixed to the shell such that plates of any tier are parallel to each other and located at the preset gap; plates of different tiers are criss-crossed at an angle of 60 degrees along the shell axles and fastened together at the crossing points. A second option includes three dividers which run through the cylinder axis; their ends are connected to the shell and are spaced at an angle of 60 degrees.

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.

A fuel assembly includes full length fuel rods which contain a plutonium fissile (Puf) but do not contain a burnable poison, full length fuel rods which contain the fissile uranium and the burnable poison, and partial length fuel rods which contain Puf but do not contain the burnable poison in a channel box. The plutonium enrichment is decreased in an order of the full length fuel rods. The concentration of the burnable poison of the full length fuel rod is higher than the concentration of the full length fuel rod. In each side of a rectangular outermost periphery adjacent to the inner surface of the channel box in a horizontal cross-sectional view of the fuel assembly, two partial length fuel rods are adjacently disposed, and the full length fuel rod containing the burnable poison is disposed to be adjacent to each partial length fuel rod.

A fuel assembly includes full length fuel rods which contain a plutonium fissile (Puf) but do not contain a burnable poison, full length fuel rods which contain the fissile uranium and the burnable poison, and partial length fuel rods which contain Puf but do not contain the burnable poison in a channel box. The plutonium enrichment is decreased in an order of the full length fuel rods. The concentration of the burnable poison of the full length fuel rod is higher than the concentration of the full length fuel rod. In each side of a rectangular outermost periphery adjacent to the inner surface of the channel box in a horizontal cross-sectional view of the fuel assembly, two partial length fuel rods are adjacently disposed, and the full length fuel rod containing the burnable poison is disposed to be adjacent to each partial length fuel rod.

Plurality of layers form a nuclear fission reactor structure, each layer having an inner segment body, an intermediate segment body, and an outer segment body (each segment body separated by an interface). The layers include a plurality of cladding arms having involute curve shapes that spirally radiate outward from a radially inner end to a radially outer end. Chambers in the involute curve shaped cladding arm contain fuel compositions (and/or other materials such as moderators and poisons). The design of the involute curve shaped cladding arms and the composition of the materials conform to neutronic and thermal management requirements for the nuclear fission reactor and are of sufficiently common design and/or have sufficiently few variations as to reduce manufacturing complexity and manufacturing variability.