Patent Number: 
Section: claims

1. A fuel assembly for a boiling water reactor, wherein during operation, the fuel assembly permits water to flow upwards through the fuel assembly, a portion of the water being transformed into steam, the fuel assembly comprising: at least one fuel bundle having a plurality of fuel units stacked on top of each other,  each fuel unit comprising a top tie plate, a bottom tie plate, and a plurality of fuel rods extending between the top tie plate and the bottom tie plate;  a steam channel comprising an empty volume that extends at least through a portion of the plurality of fuel units, between the bottom tie plate and the top tie plate of each fuel unit forming the steam channel; and  first means arranged outside the steam channel including, in one or more of the fuel units, a plurality of fuel rods arranged in a ring around the empty volume,  wherein said plurality of fuel rods are each inclined in either a clockwise or a counterclockwise direction around the empty volume,  wherein said plurality of inclined fuel rods forces the water and the steam in the plurality of fuel units to rotate around the steam channel; and  wherein the water is thrown away from the steam channel, and the steam is separated from the water and flows upwards through the steam channel. 2. The fuel assembly according to  claim 1 , wherein the steam channel has an increasing cross-sectional area towards an outlet. claim 1 3. The fuel assembly according to  claim 1 , wherein the fuel assembly comprises a plurality of parallel steam channels. claim 1 4. A fuel assembly for a boiling water reactor, wherein during operation, the fuel assembly permits water to flow upwards through the fuel assembly, a portion of the water being transformed into steam, the fuel assembly comprising: at least one fuel bundle having a plurality of fuel units stacked on top of each other,  each fuel unit comprising a top tie plate, a bottom tie plate, and a plurality of fuel rods extending between the top tie plate and the bottom tie plate;  a steam channel comprising an empty volume that extends at least through a portion of the plurality of fuel units, between the bottom tie plate and the top tie plate of each fuel unit forming the steam channel; and  first means arranged outside the steam channel comprising in at least certain of the fuel units, a majority of the fuel rods which are arranged inclined in relation to a longitudinal direction of the fuel assembly for causing the water and the steam in the plurality of fuel units to rotate around the steam channel, whereby the water is thrown away from the steam channel, whereas the steam is separated from the water and flows upwards through the steam channel,  wherein the fuel assembly comprises a plurality of parallel steam channels, and  wherein the first means causing the water and the steam in the fuel bundle to rotate around the steam channel causes the water to rotate clockwise around a first steam channel and counterclockwise around a second steam channel. 5. A fuel assembly for a boiling water reactor, wherein during operation, the fuel assembly permits water to flow upwards through the fuel assembly, a portion of the water being transformed into steam, the fuel assembly comprising: at least one fuel bundle having a plurality of fuel units stacked on top of each other,  each fuel unit comprising a top tie plate, a bottom tie plate, and a plurality of fuel rods extending between the top tie plate and the bottom tie plate;  a steam channel comprising an empty volume that extends at least through a portion of the plurality of fuel units, between the bottom tie plate and the top tie plate of each fuel unit forming the steam channel; and  first means arranged outside the steam channel comprising in at least certain of the fuel units, a majority of the fuel rods which are arranged inclined in relation to a longitudinal direction of the fuel assembly for causing the water and the steam in the plurality of fuel units to rotate around the steam channel, whereby the water is thrown away from the steam channel, whereas the steam is separated from the water and flows upwards through the steam channel,  wherein at least some of the fuel rods comprise second means for intensifying the rotation of water flow around the steam channel. 6. The fuel assembly according to  claim 5 , wherein the second means for intensifying the rotation comprises ligaments. claim 5 7. The fuel assembly according to  claim 6 , wherein the second means for intensifying the rotation comprises at least one of a top and bottom plug including fins. claim 6