Patent Number: 
Section: claims

1. A filter for separating particles from cooling water in a nuclear plant of a light water type,wherein the filter has an inlet end and an outlet end and is arranged to permit through-flow of the cooling water in a main flow direction from the inlet end to the outlet end,wherein the filter includes a number of sheets, which extend in the flow direction from the inlet end to the outlet end,wherein said sheets are arranged beside each other and form passages for the cooling water through the filter front the inlet end to the outlet end, andwherein said sheets include a first portion, which extends from the inlet end, a second portion, which extends from the outlet end, and a third portion, which extends between the first portion and the second portion,wherein said sheets along the first portion have a wave-shape formed by a number of successive waves and extending in a transverse direction transversally to the flow direction, andwherein said sheets along the third portion have a wave-shape formed by a number of successive waves and extending in the flow direction,characterized in that each wave of said wave-shape of the first portion has a maximum amplitude, wherein the maximum amplitude decreases continuously in the flow direction towards the third portion, and that said maximum amplitude is zero at a transition to the third portion. 2. A filter according to claim 1, characterized in that said wave-shapes are continuous. 3. A filter according to claim 1, characterized in that said sheets along the second portion have a wave-shape formed by a number of waves and extending in said transverse direction transversally to the flow direction. 4. A filter according to claim 1, characterized in that said sheets along the first portion ore arranged beside each other in such a way that each pair of adjacent sheets abuts each other at valleys and ridges, respectively, of said wave-shape, wherein each passage between two adjacent sheets forms a plurality of inlet channels arranged beside each other. 5. A filter according to claim 4, characterized in that said sheets along the second portion are arranged beside each other in such a way that each pair of adjacent sheets abuts each other at valleys and ridges, respectively, of said wave-shape, wherein each passage between two adjacent sheets forms a plurality of outlet channels arranged beside each other. 6. A filter according to claim 1, characterized in that said sheets are connected to each other at at least one point at said valleys and ridges, respectively. 7. A filter according to claim 6, characterized in tat said sheets are connected to each other by means of a fuse weld where the sheets abut each other. 8. A filter according to claim 6, characterized in that said sheets are connected to each other by means of a spot weld where the sheets abut each other. 9. A filter according to claim 3, characterized in that each wave of said wave-shape of the second portion has a maximum amplitude, wherein the maximum amplitude decreases continuously in the direction towards the third portion. 10. A filter according to claim 5, characterized in that each inlet channel has substantially the same flow area as each outlet channel. 11. A filter according to claim 5, characterized in that the center line of each inlet channel is concentric with the center line of a respective corresponding outlet channel. 12. A filter according to claim 1, characterized in that the third portion forms an intermediate channel between two adjacent sheets. 13. A filter according to claim 12, characterized in that the third portion includes projections extending into the intermediate channel. 14. A filter according to claim 11, characterized in that said center line of the inlet channel and the outlet channel extends between two adjacent projections of the third portion. 15. A filter according to claim 13, characterized in that said projections are firmed through plastic deformation of the sheet. 16. A filter according to claim 13, characterized in that said projections include a tab, which is out from the sheet.