Mitsubishi Nuclear Fuel Co., Ltd.

Mitsubishi Heavy Industries Limited

Mitsubishi Materials Corporation

Akio Sando

Junichi Oyama

Katsunori Ohuchi

Eiji Yoneda

Takeshi Isobe

Yoshiharu Mae

Yoshitaka Suda

Toshimichi Takahashi

Masashi Yoshida

Shuji Yamazaki

Taichi Koiwai

Minoru Murata

A fuel rod for a light water reactor comprises a cladding tube which comprises a zirconium alloy having a composition including 0.6 to 2.0% by weight of Nb, 0.5 to 1.5% by weight of Sn, 0.05 to 0.3% by weight of Fe, and the balance being Zr and incidental impurities; uranium oxide fuel pellets packed in the cladding tube; and end plugs comprising a zirconium alloy and closing both ends of the cladding tube. The cladding tube is sealed by TIG welding with the end plugs. Grain boundaries in each heat affected zone of the cladding tube, which are adjacent to a bead formed by TIG welding, have structural compositions including 4 to 30% by weight of Nb, and 0.9 to 20% by weight of Fe.

Fuel rod for light water reactor and method for manufacturing the same

A fuel rod for a light water reactor comprises a cladding tube which comprises a zirconium alloy having a composition including 0.6 to 2.0% by weight of Nb, 0.5 to 1.5% by weight of Sn, 0.05 to 0.3% by weight of Fe, and the balance being Zr and incidental impurities; uranium oxide fuel pellets packed in the cladding tube; and end plugs closing both ends of the cladding tube. The cladding tube is sealed by TIG welding with the end plugs. Precipitates having grain diameters of 0.01 to 0.5 .mu.m and comprise intermetallic compounds containing Zr, Nb and Fe are present at grain boundaries in the structure of heat affected zones of the cladding tube, the heat affected zone being adjacent to a bead formed by TIG welding.

A welding apparatus for welding an end plug on the end of a pellet filled nuclear fuel rod includes a holding mechanism, an abutting member, a torch and a pressing mechanism. The holding mechanism is for holding the external periphery of the fuel rod with the end plug attached thereto. The abutting member is disposed opposite to the holding mechanism, and the end plug of the fuel rod butts up against the abutting member. The torch is disposed between the holding mechanism and the abutting member, and is placed diametrically opposite to the external surface of the fuel rod. The holding mechanism and the abutting member are made so that the distance therebetween can be adjusted, and the pressing mechanism is provided on one of the holding mechanism or the abutting member, and operates to move the holding mechanism and the abutting member to approach each other. In a welding apparatus of such a design, the fuel rod is held by the holding mechanism, and the pressing mechanism pushes the holding mechanism toward the abutting member, and while retaining such a position at a constant compressive force, welding of the end plug is performed. Therefore, the welding is performed without being affected by the variations in the compressive force caused by welding heat distortions, thereby providing a weld of high integrity and quality.

Welding apparatus for fuel rod end plugs

An apparatus for attaching a key member to a nuclear fuel assembly grid and detaching the same therefrom is disclosed. The apparatus includes a supply and recovery mechanism, an inserting and removing mechanism, and a rotating mechanism. The supply and recovery mechanism operates to supply the key member to a prescribed position adjacent to the grid and recover the same. The inserting and removing mechanism is disposed between the supply and recovery mechanism and the grid, and operates to insert the key member supplied from the supply and recovery mechanism into the grid and remove the key member from the grid to recover the same to the supply and recovery mechanism. The rotating mechanism is disposed adjacent to the inserting and removing mechanism, and operates to rotate the key member inserted in the grid in a prescribed direction about the longitudinal axis to attach the same to the grid and rotate the same in a direction opposite to the prescribed direction to detach the same from the grid.

Apparatus for attaching key member to nuclear fuel assembly grid and

An apparatus for assembling a nuclear fuel assembly is disclosed. The apparatus includes a deflecting device which is disposed adjacent to the grid and deflects grid springs away from dimples opposing thereto. The deflecting device includes a tubular member, a rod member and a drive mechanism. The tubular member has a plurality of circumferentially divided sleeve pieces. The rod member is releasably inserted in the tubular member for sliding movement therealong. The drive mechanism is drivingly connected to the rod member and moves the rod member in the tubular member in a longitudinal direction thereof to bring the rod member into urging engagement with the sleeve pieces of the tubular member, whereby the sleeve pieces are deflected to be urged against the spring to deflect the same.

Apparatus for assembling nuclear fuel assembly

The present invention relates to an apparatus for manipulating the springs which hold the fuel rods firmly inside the grid cells of the grids in a nuclear fuel assembly. Conventionally fuel rods are inserted into the grids while the grid springs are in the active position, thus exposing the rods to possibilities of surface scratches and potential problems. The invented automatic apparatus avoids the formation of such surface damage on the fuel rods, by inserting the keys to inactivate the grid springs before inserting the fuel rods into the grids and removing the keys after all the rods are in place. The apparatus thus contributes to efficient manufacturing of the fuel assembly by simplifying the key quantity management operations and other tasks associated with the assembling operations.

Apparatus for operating the grid springs of nuclear fuel assembly

The present invention presents a method and an apparatus for assembling a fuel assembly which is free of surface damage on the fuel rod surfaces, and of distortions caused by residual stresses. Such problems are introduced by the method of inserting the fuel rods into the grids, and the sequence of attaching the control rod guiding pipes. In the conventional method, the guiding pipes are attached to the respective grids first and the fuel rods are inserted in the grids while the holding mechanisms (such as spring force against a dimple formed on the grid wall) are active. In the invented assembling method, the sprigs are deactivated first and then the fuel rods are inserted into the grids. Once the assembly is made firm with all the fuel rods in place and fixed firmly to the grids, the control rod guiding pipes are inserted into the grids and the pipes are fixed rigidly to the respective grids. By performing the assembling operation in the above sequence, slight shifting of the grids which occurs on fixing the pipes to the grids, during the conventional method, is prevented. The final assembly produced according to the invented method is free of surface damage and the overall quality of alignment of the assembly is excellent.

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Ibaraki, Japan

Akio Sando