Mitsubishi Nuclear Fuel Co., Ltd.

Mitsubishi Jukogyo Kabushiki Kaisha

Hiromasa Miyai

Junichi Oyama

Masaji Mori

Toshiyuki Kawagoe

Hitoshi Inada

Kazuichi Suzuki

Akihiro Kato

Akhirio Kato

An arrangement of fuel rod support members having dimples and springs is presented to prevent abrasive wear of the fuel rods caused by bouncing of the fuel rods against the supporting members caused by vibrations in a diagonal direction of the support grids. The supporting members are disposed such that dimples are respectively provided on one pair of adjacent walls located on one side of the vibrational direction while springs are respectively provided on adjacent walls located on the opposite side of the vibrational direction.

Fuel assembly

A fuel assembly is presented in which a plurality of support grids are disposed along the longitudinal direction of the fuel rods. The straps forming the grid cells of the support grids are provided with mixing vanes for generating turbulent flow of the cooling water passing through the grid cells. In a plan view of the support girds, each of the mixing vanes protrudes inwardly of the grid cells and is disposed along a positive diagonal direction and a negative diagonal direction. This configuration of the mixing vanes are effective in preventing the generation of systematic vibrations in the fuel assembly by canceling the effects of the turbulent flows of the cooling water. The direction of protrusion of the mixing vanes can be in two diagonal directions within one support grid, or it can be unidirectional along either diagonal direction within one support grid.

In a method of assembling a nuclear fuel assembly, a deflecting jig is inserted into grid cells in each of a plurality of grids. The diameter of the deflecting jig is enlarged to urge a spring of at least one pair of dimples and spring associated with the grid cell to deflect the springs away from the dimple. A plurality of elongated key members are inserted into the grid cells through a plurality of openings defined at intersections between the straps forming walls of the grid cells. Each key member is rotated about its axis to cause hooks of the key member to project from a wall surface of the strap in a direction opposite to the projecting direction of the springs. The key member is then moved in a direction to engage the hooks with the wall surface of the strap. Urging of the spring by the deflecting jig is released to allow the same to be withdrawn from the grid cells and, subsequently, the fuel rods are inserted into the respective grid cells. The key member is then moved in a direction to bring the springs into pressure contact with the fuel rods. The key members are then withdrawn from the grid cells.

Assembly method and grid for nuclear fuel assembly

In a method of assembling a nuclear fuel assembly, a deflecting jig is inserted into grid cells in each of a plurality of grids. The diameter of the deflecting jig is enlarged to urge a spring of at least one pair of dimples and spring, associated with the grid cell to deflect the springs away from the dimple. A plurality of elongated key members are inserted into the grid cells through a plurality of openings defined at intersections between the straps forming walls of the grid cells. Each key member is rotated about its axis to cause hooks of the key member to project from a wall surface of the strap in a direction opposite to the projecting direction of the springs. The key member is then moved in a direction to engage the hooks with the wall surface of the strap. Urging of the spring by the deflecting jig is released to allow the same to be withdrawn from the grid cells and, subsequently, the fuel rods are inserted into the respective grid cells. The key member is then moved in a direction to bring the springs into pressure contact with the fuel rods. The key members are then withdrawn from the grid cells. A combination of the grid and the key member is also provided.

In a grid in a nuclear fuel assembly for supporting fuel rods, elongated straps intersect with each other to define grid cells. At least one pair of punched sections are formed, in spaced relation to each other, in each of peripheral walls of the respective grid cells. At least one of elongated spring elements is formed in the peripheral wall of each grid cell. Each spring element is formed such that a portion of the peripheral wall of the grid cell between the pair of punched sections bulges and projects into the grid cell. The spring element is capable of being deflected toward the peripheral wall of the grid cell. A pair of projections are formed in the peripheral wall of the grid cell respectively at both longitudinal ends of the spring element such that a pair of portions of the peripheral wall of the grid cell bulge. Both longitudinal ends of the spring element are connected respectively to the pair of projections.

Grid in a nuclear fuel assembly

In a method of assembling a nuclear fuel assembly, a deflecting jig is inserted into grid cells in each of a plurality of grids. The diameter of the deflecting jig is enlarged to urge a spring of at least one pair of dimples and spring associated with the grid cell to deflect the spring away from the dimple. A plurality of elongated key members are inserted into the grid cells through a plurality of openings defined at intersections between the straps forming walls of the grid cells. Each key member is rotated about its axis to cause hooks of the key member to project from a wall surface of the strap in a direction opposite to the projecting direction of the springs. The key member is then moved in a direction to engage the hooks with the wall surface of the strap. Urging of the spring by the deflecting jig is released to allow the same to be withdrawn from the grid cells and, subsequently, the fuel rods are inserted into the respective grid cells. The key number is then moved in a direction to bring the springs into pressure contact with the fuel rods. The key members are then withdrawn from the grid cells.

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Kobe, Japan

Hiromasa Miyai