Abstract: A fuel assembly for a pressurized water nuclear reactor includes a multiplicity of fuel rods which extend in a longitudinal direction and are guided in a plurality of spacers that are spaced apart from one another axially. The spacers of an upper region have a lower flow resistance in a transverse direction perpendicular to the longitudinal direction, than the spacers of a lower region.

Abstract: A grid (13) for supporting nuclear fuel pencils (3) for a nuclear fuel assembly (1) comprising a peripheral belt (17), the peripheral belt (17) comprising on at least one of its edges (35, 37) guide fins (33) is disclosed. The edge (35, 37) of the peripheral belt (17) has between the adjacent guide fins (33) recesses (39) towards the inside of the grid (13). The invention is applicable, for example, to pressurized water reactors.

Abstract: A fuel assembly for a pressurized water nuclear reactor contains a multiplicity of fuel rods which are guided in a plurality of axially spaced spacers which in each case form a square grid, composed of grid webs, with a multiplicity of cells arranged in rows and columns. In each case one control rod guide tube is guided through a number of these cells. At least one spacer is configured to be mechanically stronger in a first partial region than in a second partial region. In this second partial region, the spacer is provided with at least one resisting element which protrudes into a flow sub-channel formed between the fuel rods and increases the flow resistance. The resisting element counteracts a reduction associated with the mechanically weaker configuration, in the flow resistance in the second partial region and in this manner effects a homogenization of the hydraulic behavior of a spacer which is mechanically inhomogeneous on account of the varying mechanical configuration.

Abstract: The core of a pressurized water reactor is assembled in such a way that if the fuel elements on the edge of the core are bent, these fuel elements are oriented such that the bending of the fuel elements points outwards in a convex manner. When the reactor is in operation, forces arise which increase the size of small gaps between the fuel elements at the expense of greater gaps and counteract the bending effect of the fuel elements.

Abstract: A fuel assembly for a pressurized water nuclear reactor contains a multiplicity of fuel rods which are guided in a plurality of axially spaced spacers which in each case form a square grid, composed of grid webs, with a multiplicity of cells arranged in rows and columns. In each case one control rod guide tube is guided through a number of these cells. At least one spacer is configured to be mechanically stronger in a first partial region than in a second partial region. In this second partial region, the spacer is provided with at least one resisting element which protrudes into a flow sub-channel formed between the fuel rods and increases the flow resistance. The resisting element counteracts a reduction associated with the mechanically weaker configuration, in the flow resistance in the second partial region and in this manner effects a homogenization of the hydraulic behavior of a spacer which is mechanically inhomogeneous on account of the varying mechanical configuration.

Abstract: A fuel element for a pressurized water reactor has fuel rods guided through a number of axially spaced spacers. The spacers form a square grid with mesh openings arranged in rows and columns. Support tubes that do not contain fuel pass through a number of the mesh holes and are joined to the meshes . The support tubes are spread out in positions within the grid with a predetermined number of support tubes and a distribution thereof within the grid, which is rotationally symmetric about 90° with regard to a rotation about the central axis of the spacer, the central axis is perpendicular to the grid plane, the number of rows and columns that do not contain any support tubes is minimal. Optionally, remaining inner rows and columns that do not contain any support tubes are not situated next to one another.

Abstract: A fuel assembly for a pressurized water nuclear reactor includes a multiplicity of fuel rods which extend in a longitudinal direction and are guided in a plurality of spacers that are spaced apart from one another axially. The spacers of an upper region have a lower flow resistance in a transverse direction perpendicular to the longitudinal direction, than the spacers of a lower region.

Abstract: A grid (13) for supporting nuclear fuel pencils (3) for a nuclear fuel assembly (1) comprising a peripheral belt (17), the peripheral belt (17) comprising on at least one of its edges (35, 37) guide fins (33) is disclosed. The edge (35, 37) of the peripheral belt (17) has between the adjacent guide fins (33) recesses (39) towards the inside of the grid (13). The invention is applicable, for example, to pressurized water reactors.

Abstract: A fuel assembly for a pressurized-water nuclear reactor contains a plurality of grid-shaped, square spacers spaced apart from one another. Each of the grid-shaped, square spacers has four edge webs. At least one of the spacers has at least two differently configured edge webs for generating a force which acts from a flowing cooling water on the fuel assembly in a plane of the spacer transversely with respect to an axial direction. A multiplicity of fuel rods extend in the axial direction and are guided in the plurality of grid-shaped, square spacers.

Abstract: A fuel assembly for a compressed water nuclear reactor contains a plurality of fuel rods that are guided into a plurality of axially interspaced spacers respectively forming a quadratic grid formed of connecting elements and containing a plurality of holes that are disposed in rows and columns. A control rod guiding tube is respectively guided through a number of the holes, and the spacer is structurally embodied in such a way that when a limiting force acting laterally on the spacer is exceeded, a deformation is triggered exclusively in a region of the spacer located outside an inner region containing the control rod guiding tubes.

Abstract: A fuel assembly for a pressurized water reactor has a plurality of fuel rods that are guided inside a plurality of axially spaced-apart spacers that are composed of grid webs. Each grid web forms a grid with a multitude of grid cells disposed in rows and columns. The grid webs are provided with flow guides for generating a cooling water current encompassing a transversal flow component that is oriented parallel to the spacer plane. At least one spacer is formed of a multitude of sub-regions, each of which is greater than one grid cell. The flow guides are configured and distributed within the spacer in such a way that in the wake above each sub-region, a transverse flow distribution is created which causes cooling water to be exchanged at least almost exclusively between secondary flow ducts located within the sub-region.

Abstract: A fuel element for a pressurized water reactor has fuel rods guided through a number of axially spaced spacers. The spacers form a square grid with a multitude of mesh openings arranged in rows and columns. Support tubes that do not contain fuel are passed through a number of the mesh holes and are joined with a material bond to the meshes inside the spacer. The support tubes are spread out in positions within the grid in such a manner that, with a predetermined number of support tubes and a distribution thereof within the grid, which is rotationally symmetric about 90° with regard to a rotation about the central axis of the spacer, said central axis being perpendicular to the grid plane, the number of rows and columns that do not contain any support tubes is minimal. In addition, it is ensured that optionally remaining inner rows and columns that do not contain any support tubes are not situated next to one another.

Abstract: Transverse vibrations of the pellet columns included in the fuel rods of fuel elements are limited by elastically mounting the fuel rod jacket tubes in the mesh of spacer grids. When the fuel rods are supported in this way, flexural vibrations of a higher order occur that lead to damage to the jacket tubes caused by fretting. These vibrations are the less dampened the more rigid the fixture of the fuel rod is. These vibration conditions are more easily excited and more strongly dampened when the pellet columns are more mobile, thereby removing vibration energy from the fuel element and avoiding damage caused by fretting. The mobility of the columns can be increased by increasing the gap between the pellet and the jacket tube, or by using constructions in which a torque M?10 N mm on the fuel rod leads to a tilting angle ??0.1°.

Abstract: Transverse vibrations of the pellet columns included in the fuel rods of fuel elements are limited by elastically mounting the fuel rod jacket tubes in the mesh of spacer grids. When the fuel rods are supported in this way, flexural vibrations of a higher order occur that lead to damage to the jacket tubes caused by fretting. These vibrations are the less dampened the more rigid the fixture of the fuel rod is. These vibration conditions are more easily excited and more strongly dampened when the pellet columns are more mobile, thereby removing vibration energy from the fuel element and avoiding damage caused by fretting. The mobility of the columns can be increased by increasing the gap between the pellet and the jacket tube, or by using constructions in which a torque M≦10 N mm on the fuel rod leads to a tilting angle &phgr;≧0.1°.

Abstract: The core of a pressurized water reactor is assembled in such a way that if the fuel elements on the edge of the core are bent, these fuel elements are oriented such that the bending of the fuel elements points outwards in a convex manner. When the reactor is in operation, forces arise which increase the size of small gaps between the fuel elements at the expense of greater gaps and counteract the bending effect of the fuel elements.

Abstract: A pressure vessel of a pressurized-water reactor has an upper part in which coolant is collected in a plenum. The coolant enters the plenum through a grid plate on which tops of the fuel assemblies are supported and the coolant is removed from the plenum laterally. Support columns and control-rod guideways form obstacles to the flow of the coolant which can lead to damming-up below the grid plate with horizontal pressure differences and corresponding horizontal flows. Throttle plates inserted in the top of the fuel assemblies or throttle inserts in apertures in the grid plate produce a uniform pressure in the coolant below the grid plate so that it flows uniformly and in a vertical direction through the individual fuel assemblies.