Patent Number: 
Section: claims

1. A core plate assembly for a boiling water reactor of nuclear plant, comprising:a core plate having a plurality of through-going apertures;a beam structure comprising a plurality of parallel first beams and a plurality of parallel second beams being perpendicular to the first beams, wherein the first and second beams enclose a plurality of rectangular areas beneath the core plate, wherein each of the rectangular areas encloses four of said through-going apertures;a plurality of control rod guide tubes, each being aligned with a respective one of the through-going apertures; anda plurality of transition pieces, each being received in a respective one of the control rod guide tubes, and each having four passages for communicating with a respective fuel assembly, each passage permitting a coolant flow into the respective fuel assembly,wherein a respective flow inlet for the coolant into each passage is provided,wherein at least one of the flow inlets has a non-circular cross-sectional shape, wherein the non-circular cross-sectional shape comprises a circular hole with a first recess extending therefrom. 2. A core plate assembly according to claim 1, wherein the first recess extends in sideward direction from the circular hole. 3. A core plate assembly according to claim 1, wherein the cross-sectional shape of the at least one flow inlet comprises a second recess extending in sideward direction from the circular hole. 4. A core plate assembly according to claim 3, wherein the first recess and the second recess are provided opposite to each other. 5. A core plate assembly according to claim 1, wherein the flow inlet is located between an upper end of the first and second beams and a lower end of the first and second beams. 6. A core plate assembly according to claim 1, wherein the at least one flow inlet is located opposite to a corner between one of the first beams and one of the second beams. 7. A core plate assembly according to claim 1, wherein the flow inlet extends through a first hole through the transition piece and a second hole through the control rod guide tube. 8. A core plate assembly according to claim 7, wherein the cross-sectional shape of the at least one flow inlet is determined by the first hole. 9. A core plate assembly according to claim 7, wherein the cross-sectional shape of the at least one flow inlet is determined by the second hole. 10. A core plate assembly according to claim 7, wherein a sheet is provided between the transition piece and the control rod guide tube, wherein the flow inlet extends through a third hole through the sheet, and wherein the cross-sectional shape of the at least one flow inlet is determined by the third hole. 11. A core plate assembly according to claim 10, wherein the sheet is joined to the transition piece. 12. A method of performing work on a core plate assembly of a boiling water reactor of a nuclear plant, the core plate assembly comprising:a core plate having a plurality of through-going apertures,a beam structure comprising a plurality of parallel first beams and a plurality of parallel second beams being perpendicular to the first beams, wherein the first and second beams enclose a plurality of rectangular areas beneath the core plate, wherein each of the rectangular areas encloses four of said through-going apertures,a plurality of control rod guide tubes, each being received in a respective one of the through-going apertures, anda plurality of transition pieces, each being received in a respective one of the control rod guide tubes, and each having four passages for receiving a respective fuel assembly, each passage permitting a coolant flow into the respective fuel assembly,wherein a respective flow inlet for the coolant into each passage is provided,the method comprising the steps of:removing one of the fuel assemblies from the boiling water reactor,introducing an elongated tool into the boiling water reactor and into the passage from which said fuel assembly was removed;positioning a tool head of the elongated tool in the proximity of the flow inlet of said passage; andactuating the tool head to cut said flow inlets to a non-circular cross-sectional shape.