Patent Number: 051981858
Section: claims

1. In a nuclear reactor having fuel in the form of a core and a plenum above said core, said core having a center and a periphery, said plenum receiving coolant, apparatus comprising: a plurality of hollow sleeves for housing said fuel, said sleeves having an upper portion and a lower portion, said upper portion in said plenum, said lower portion below said plenum, said fuel positioned in said lower portion, said sleeves having holes formed in said upper portion to admit said coolant to the interior of said sleeves, said holes admitting varying amounts of coolant from sleeve to sleeve, said amount being greater in sleeves located toward said center of said core than toward said periphery of said core.  boring at least two different sets of holes in said upper portion of said sleeves, said different sets capable of admitting different amounts of coolant therethrough;  distributing said sleeves about said core so that said sleeves capable of admitting the highest amount of coolant are placed toward said center of said core and those capable of admitting the least amount of coolant are placed toward said periphery of said core. 2. The apparatus as recited in claim 1, wherein said holes have the same diameter and the number of holes in sleeves located toward said center of said core is greater than the number of holes located toward said periphery of said core. 3. The apparatus as recited in claim 1, wherein said holes are arranged in rows and the number of said rows is varied from sleeve to sleeve, said number of rows being greater in sleeves toward said center of said core than toward said periphery of said core so that the amount of coolant entering the interior of said sleeves toward said center of said core is greater than the amount of water entering the interior of said sleeves toward said periphery of said core. 4. The apparatus as recited in claim 1, wherein said holes are of equal diameter and arranged in rows and the number of said rows is varied from sleeve to sleeve, said number of rows being greater in sleeves toward said center of said core than toward said periphery of said core so that the amount of coolant entering the interior of said sleeves toward said center of said core is greater than the amount of coolant entering the interior of said sleeves toward said periphery of said core. 5. The apparatus as recited in claim 1, wherein said upper portion has a top and a bottom and said holes are arranged in rows beginning at said bottom of said upper portion, whereby said sleeves near said center of said core have more rows, said rows extending more toward said top from said bottom of said upper portion than sleeves located near said periphery of said core. 6. The apparatus as recited in claim 1, wherein said upper portion has a top and a bottom and said holes are of equal diameter and are arranged in rows beginning at said bottom of said upper portion, whereby said sleeves near said center of said core have more rows of holes, said rows extending more toward said top from said bottom of said upper portion than sleeves located near said periphery of said core. 7. In a nuclear reactor having a plurality of hollow sleeves forming a core, said core having a center and a periphery, said sleeves having an upper portion and a lower portion, and a plenum disposed about said upper portion of said sleeves, said plenum receiving coolant, a method for cooling said core comprising the steps of: 8. The method as recited in claim 7, wherein said holes have the same diameter and said at least two different sets each has a different number of holes. 9. The method as recited in claim 7, wherein said upper portion has a top and a bottom and said holes are bored in rows beginning at said bottom, and each set of said at least two sets has a different number of rows of holes. 10. The method as recited in claim 7, wherein said holes have the same diameter, said upper portion has a top and a bottom and said holes are bored in rows beginning at said bottom, and each set of said at least two sets has a different number of rows of holes.