Patent Number: 
Section: claims

1. A fuel assembly for a nuclear boiling water reactor, the fuel assembly comprising a plurality of spacers wherein at least one of said spacers comprises a plurality of cells for holding parallel elongated elements extending through the cells or for allowing said elements to pass through the cells, wherein a plurality of flow channels are defined between the cells which flow channels allow a cooling medium to flow therethrough, wherein, when the fuel assembly is in use in a nuclear boiling water reactor, the elongated elements extend in an essentially vertical direction and the flow of the cooling medium takes place mainly in a vertical direction upwards, wherein at least one of said spacers comprises a plurality of deflecting members which are arranged to deflect the flow of the cooling medium, wherein said plurality of said deflecting members comprises a vane which extends in a direction from a cell into the neighboring flow channel, wherein the vane is inclined relative to a vertical plane, wherein the vane is wider in its upper part than in its lower part, wherein there is only one vane per flow channel, wherein the deflecting member also comprises a plane or somewhat bent base portion which has an extension in a vertical direction, wherein the vane and the base portion form a continuous unit, wherein the vane is folded-out from the base portion and thus meets the base portion along a line, wherein the base portion constitutes a continuous unit together with a cell, wherein the vane is formed as a folded-out portion of the cell, and wherein the vane is folded-out such that it forms an angle of about 75-120 degrees with the base portion. 2. A fuel assembly according to  claim 1 , characterized in that the base portion is configured and arranged such that, when the spacer is positioned for use in a nuclear boiling water reactor, it extends parallel to one of said neighboring elongated elements. claim 1 3. A fuel assembly according to  claim 1 , characterized in that the vane extends towards and reaches about the middle of the flow channel. claim 1 4. A fuel assembly according to  claim 1 , characterized in that the vane is planar. claim 1 5. A fuel assembly according to  claim 1 , characterized in that the vane is bent. claim 1 6. A fuel assembly according to  claim 1 , characterized in that the vane has a first edge which extends in at least a vertical direction and which is closer to the cell in its lower part than in its upper part and a second edge which extends in at least a horizontal direction and which meets the first edge in a corner portion. claim 1 7. A fuel assembly according to  claim 6 , characterized in that the first and second edges are straight. claim 6 8. A fuel assembly according to  claim 6 , characterized in that at least one of the first and the second edges is bent. claim 6 9. A fuel assembly according to  claim 8 , characterized in that said corner portion is located at approximately the same level as or higher up than the portion of the second edge which is closer to the cell, such that a vortex formed by the vane in the flow of the cooling medium is relieved from the vane primarily at said corner portion. claim 8 10. A fuel assembly for a nuclear boiling water reactor, the fuel assembly comprising a plurality of spacers wherein at least one of said spacers comprises a plurality of cells for holding parallel elongated elements extending through the cells or for allowing said elements to pass through the cells, wherein a plurality of flow channels are defined between the cells which flow channels allow a cooling medium to flow therethrough, wherein, when the fuel assembly is in use in a nuclear boiling water reactor, the elongated elements extend in an essentially vertical direction and the flow of the cooling medium takes place mainly in a vertical direction upwards, wherein at least one of said spacers comprises a plurality of deflecting members which are arranged to deflect the flow of the cooling medium, wherein said plurality of said deflecting members comprises a vane which extends in a direction from a cell into the neighboring flow channel, wherein the vane is inclined relative to a vertical plane, wherein the vane is wider in its upper part than in its lower part, wherein there is only one vane per flow channel, wherein the vane has a first edge which extends in at least a vertical direction and which is closer to the cell in its lower part than in its upper part and a second edge which extends in at least a horizontal direction and which meets the first edge in a corner portion, and wherein said comer portion is located at approximately the same level as or higher up than the portion of the second edge which is closer to the cell, such that a vortex formed by the vane in the flow of the cooling medium is relieved from the vane primarily at said corner portion. 11. A fuel assembly for a nuclear boiling water reactor, the fuel assembly comprising a plurality of spacers wherein at least one of said spacers comprises a plurality of cells for holding parallel elongated elements extending through the cells or for allowing said elements to pass through the cells, wherein a plurality of flow channels are defined between the cells which flow channels allow a cooling medium to flow therethrough, wherein, when the fuel assembly is in use in a nuclear boiling water reactor, the elongated elements extend in an essentially vertical direction and the flow of the cooling medium takes place mainly in a vertical direction upwards, wherein at least one of said spacers comprises a plurality of deflecting members which are arranged to deflect the flow of the cooling medium, wherein said plurality of said deflecting members comprises a vane which extends in a direction from a cell into the neighboring flow channel, wherein the vane is inclined relative to a vertical plane, wherein the vane is wider in its upper part than in its lower part, wherein there is only one vane per flow channel, wherein the vane has a first edge which extends in at least a vertical direction and which is closer to the cell in its lower part than in its upper part and a second edge which extends in at least a horizontal direction and which meets the first edge in a corner portion, and wherein the vane is inclined between 5 and 30 degrees relative to a vertical plane. 12. A fuel assembly for a nuclear boiling water reactor, the fuel assembly comprising a plurality of spacers wherein at least one of said spacers comprises a plurality of cells for holding parallel elongated elements extending through the cells or for allowing said elements to pass through the cells, wherein a plurality of flow channels are defined between the cells which flow channels allow a cooling medium to flow therethrough, wherein, when the fuel assembly is in use in a nuclear boiling water reactor, the elongated elements extend in an essentially vertical direction and the flow of the cooling medium takes place mainly in a vertical direction upwards, wherein at least one of said spacers comprises a plurality of deflecting members which are arranged to deflect the flow of the cooling medium, wherein said plurality of said deflecting members comprises a vane which extends in a direction from a cell into the neighboring flow channel, wherein the vane is inclined relative to a vertical plane, wherein the vane is wider in its upper part than in its lower part, wherein there is only one vane per flow channel, wherein the vane has a first edge which extends in at least a vertical direction and which is closer to the cell in its lower part than in its upper part and a second edge which extends in at least a horizontal direction and which meets the first edge in a corner portion, and wherein the vane is inclined between 5 and 30 degrees relative to a vertical plane. 13. A fuel assembly according to  claim 12 , characterized in that the vane in a vertical direction reaches higher than the cells. claim 12 14. A fuel assembly according to  claim 12 , characterized in that the vane in a vertical direction has an extension which neither reaches essentially above or essentially below the cells. claim 12 15. A fuel assembly for a nuclear boiling water reacter, the fuel assembly comprising a plurality of spacers wherein at least one of said spacers comprises a plurality of cells for holding parallel elongated elements extending through the cells or for allowing said elements to pass through the cells, wherein a plurality of flow channels are defined between the cells which flow channels allow a cooling medium to flow therethrough, wherein, when the fuel assembly is in use in a nuclear boiling water reactor, the elongated elements extend in an essentially vertical direction and the flow of the cooling medium takes place mainly in a vertical direction upwards, wherein at least one of said spacers comprises a plurality of deflecting members which are arranged to deflect the flow of the cooling medium, wherein said plurality of said deflecting members comprises a vane which extends in a direction from a cell into the neighboring flow channel, wherein the vein is inclined relative to a vertical plane, wherein the vane is wider in its upper part than in its lower part, wherein there is only one vein per flow channel, wherein the deflecting member also comprises a plane or somewhat bent base portion which has an extension in a vertical direction, wherein the vane and the base portion form a continuous unit, wherein the vein is folded-out from the base portion and thus meets the base portion along a line, and wherein the vein is inclined between 5 and 30 degrees relative to a vertical plane.