Patent Number: 053295714
Section: claims

1. A reactor core for a boiling water nuclear reactor with a plurality of vertical fuel assemblies (40, 42, 44), each fuel assembly containing a bottom-tie plate (11),  a top-tie plate (12),  a plurality of fuel rods (10) arranged between the bottom-tie plate and the top-tie plate,  a vertical casing (6) surrounding the fuel rods,  a number of spacers (13, 13a-f) for retaining the fuel rods in a spaced relationship,  an inlet (3) for conducting water in through the bottom-tie plate through the space between the fuel rods and out through the top-tie plate, and gaps (37a,37b) between the fuel assemblies, said gaps being traversed with water in a vertical direction from below and upwards through the core,  a bottom-tie plate (11),  a top-tie plate (12),  a plurality of fuel rods (10) arranged between the bottom-tie plate and the top-tie plate,  a vertical casing (6) surrounding the fuel rods,  a number of spacers (13, 13a-f) for retaining the fuel rods in a spaced relationship,  an inlet (3) for conducting water in through the bottom-tie plate through the space between the fuel rods and out through the top-tie plate,  a hollow support member (7) of cruciform cross section forming  a cruciform space (32), for conducting water in a vertical direction from below and upwards through the fuel assembly, and gaps (37a,37b) between the fuel assemblies, said gaps being traversed with water in a vertical direction from below and upwards through the core,  a bottom-tie plate (11),  a top-tie plate (12),  a plurality of fuel rods (10) arranged between the bottom-tie plate and the top-tie plate,  a vertical casing (6) surrounding the fuel rods,  a number of spacers (13, 13a-f) for retaining the fuel rods in a spaced relationship,  an inlet (3) for conducting water in through the bottom-tie plate through the space between the fuel rods and out through the top-tie plate,  a hollow support member (7) of cruciform cross section forming  a cruciform space (32), for conducting water in a vertical direction from below and upwards through the fuel assembly, and gaps (37a,37b) between the fuel assemblies, said gaps being traversed with water in a vertical direction from below and upwards through the core,  a bottom-tie plate (11),  a top-tie plate (12),  a plurality of fuel rods (10) arranged between the bottom-tie plate and the top-tie plate,  a vertical casing (6) surrounding the fuel rods,  a number of spacers (13, 13a-f) for retaining the fuel rods in a spaced relationship,  an inlet (3) for conducting water in through the bottom-tie plate through the space between the fuel rods and out through the top-tie plate,  a channel (45) arranged internally in the fuel assembly for conducting water in a vertical direction from below and upwards through the fuel assembly,  a wall (46) surrounding the channel, and gaps (37a,37b) between the fuel assemblies, said gaps being traversed with water in a vertical direction from below and upwards through the core, 2. A reactor core according to claim 1, wherein said outlet holes (43) are arranged at a level below the two uppermost spacers (13a, 13b). 3. A reactor core according to claim 2, wherein the total area of the outlet holes (43) constitutes 5-80% of the flow area in the fuel assembly. 4. A reactor core according to claim 2, wherein the total area of the outlet holes (43) constitutes 20-40% of the flow area in the fuel assembly. 5. A reactor core according to claim 2, wherein the percentage of the fuel assemblies (40, 42, 44) which are arranged with outlet holes for water constitute 10-75% of the total number of fuel assemblies in the core. 6. A reactor core for a boiling water nuclear reactor with a plurality of vertical fuel assemblies (40), each fuel assembly containing 7. A reactor core according to claim 6, wherein said outlet holes (43,41) are arranged at a level below the two uppermost spacers (13a, 13b). 8. A reactor core according to claim 7, wherein the total area of the outlet holes (43,41) constitutes 5-80% of the flow area in the fuel assembly. 9. A reactor core according to claim 7, wherein the total area of the outlet holes (43,41) constitutes 20-40% of the flow area in the fuel assembly. 10. A reactor core according to claim 7, characterized in that the percentage of the fuel assemblies (40) which are arranged with outlet holes for water constitute 10-75% of the total number of fuel assemblies in the core. 11. A reactor core for a boiling water nuclear reactor with a plurality of vertical fuel assemblies (40), each fuel assembly containing 12. A reactor core according to claim 1, wherein said outlet holes (41) are arranged at a level below the two uppermost spacers (13a, 13b). 13. A reactor core according to claim 12, wherein the total area of the outlet holes (41) constitutes 5-80% of the flow area in the fuel assembly. 14. A reactor core according to claim 12, wherein the total area of the outlet holes (41) constitutes 20-40% of the flow area in the fuel assembly. 15. A reactor core according to claim 12, wherein the percentage of the fuel assemblies (40) which are arranged with outlet holes for water constitute 10-75% of the total number of fuel assemblies in the core. 16. A reactor core for a boiling water nuclear reactor with a plurality of vertical fuel assemblies (44), each fuel assembly containing 17. A reactor core according to claim 16, characterized in that said outlet holes (43,47) are arranged at a level below the two uppermost spacers (13a, 13b). 18. A reactor core according to claim 17, characterized in that the total area of the outlet holes (43,47) constitutes 5-80% of the flow area in the fuel assembly. 19. A reactor core according to claim 17, characterized in that the total area of the outlet holes (43,47) constitutes 20-40% of the flow area in the fuel assembly. 20. A reactor core according to claim 17, characterized in that the percentage of the fuel assemblies (44) which are arranged with outlet holes for water constitute 10-75% of the total number of fuel assemblies in the core.