Patent Number: 062597566
Section: claims

1. In a nuclear reactor having a core, said core including plural control blades and fuel assemblies with each control blade operationally associated with four fuel bundles of each fuel assembly, sets of said control blades forming discrete control blade groups forming a core pattern including first and second main groups thereof, respectively, symmetrically and asymmetrically arranged about the core, each main group having first and second sub-groups, said first sub-groups of said main group including first and second operational sub-groups, respectively, of control blades; each first sub-group of said first main group being flanked by first sub-groups of said second main group in a first direction and by the second sub-group of said second main group in a second direction normal to said first direction;  each second sub-group of said first main group being flanked by second sub-groups of said second main group in said first direction and by first sub-groups of said second main group in the second direction;  each first sub-group of said second main group being flanked by a first sub-group of said first main group in the first direction and by said second sub-group of said first main group in the second direction;  each second sub-group of said second main group being flanked by a second sub-group of said first main group in the first direction and by the first sub-group of said first main group in the second direction;  each blade of each first main group being movable between withdrawn, deep and shallow positions relative to said core and said fuel bundles associated with said first main group, each blade of each second main group being movable between withdrawn and shallow positions relative to said core and to fuel bundles associated with said second main group;  a method of operating the nuclear reactor comprising the steps of:  inserting into the core from a withdrawn position into a deep position a different sub-group of the blades of the first and second sub-groups and operational sub-groups of said first main group at the beginning of at least each of three successive time periods, respectively, with predetermined sub-groups of blades of said first and second main groups withdrawn from the core at the beginning of each said successive time period;  inserting into the core from a withdrawn position into a shallow position a different sub-group of the blades of the first and second sub-groups of said first and second main groups at the beginning of each of said successive time periods with said predetermined sub-groups of blades of said first and second main groups withdrawn from the core at the beginning if each said successive time period; and  maintaining selected sub-groups of said withdrawn blades at the beginning of each successive time period in a withdrawn position for at least two consecutive time periods.  a method of operating the nuclear reactor comprising the steps of:  inserting into the core from a withdrawn position into a deep position different selected blades of the first and second sub-groups of said first main group at the beginning of at least each of three successive time periods, respectively, with predetermined sub-groups of blades of said first and second main groups withdrawn from the core at the beginning of each said successive time period;  inserting into the core from a withdrawn position into a shallow position different selected blades of the first and second sub-groups of said first and second main groups at the beginning of each of said successive time periods with said predetermined sub-groups of blades of said first and second main groups withdrawn from the core at the beginning if each said successive time period; and  maintaining selected withdrawn blades at the beginning of each said successive time period in a withdrawn position for at least two consecutive time periods. 2. A method according to claim 1 wherein any one control blade of said plural control blades remains withdrawn for at least two consecutive time periods after having been withdrawn from an inserted position. 3. A method according to claim 1, including the further steps of inserting into the core from a withdrawn position into a deep position said first sub-groups of control blades of said first main group at the beginning of a predetermined time period, withdrawing said first sub-groups of control blades of said first main group at the end of said predetermined time period, and maintaining said first sub-groups of said control blades of said first main group withdrawn from said core for at least two consecutive time periods immediately subsequent to said predetermined time period. 4. A method according to claim 3 including the further steps of inserting into said core from a withdrawn position into a shallow position the first operational sub-groups of said first sub-group of said first main group at the beginning of said predetermined time period, withdrawing said first operational sub-groups of said first sub-group of said first main group at the end of said predetermined time period and maintaining said first operational sub-groups of said first sub-group of said first main group withdrawn from said core for at least two consecutive time periods immediately subsequent to said predetermined time period. 5. A method according to claim 4 wherein any one control blade of said plural control blades remains withdrawn for at least two consecutive time periods after having been withdrawn from an inserted position. 6. A method according to claim 1, including the further steps of inserting into the core from a withdrawn position into a shallow position the second sub-group of said second main group of control blades at the beginning of a predetermined time period and maintaining said second sub-groups of said second main group of control blades withdrawn from said core for at least two consecutive time periods, immediately subsequent to said predetermined time period. 7. A method according to claim 1, including the further steps of inserting into the core from a withdrawn position into a deep position the operational sub-groups of said second sub-group of said first main group of control blades at the beginning of a predetermined time period, withdrawing said second operational sub-groups of said second sub-group of said first main group at the end of said predetermined time period and maintaining said second operational sub-groups of said first main group of said control blades withdrawn from said core for at least two consecutive time periods immediately following said predetermined time period. 8. A method according to claim 1, including the further steps of inserting into the core from a withdrawn position into a deep position said second sub-groups of said first main group of control blades at the beginning of a predetermined time period, withdrawing said second sub-groups of said first main group at the end of said predetermined time period and maintaining said second sub-groups of said first main group withdrawn from said core for at least two consecutive time periods immediately subsequent to said predetermined time period. 9. A method according to claim 8 including the further steps of inserting into said core from a withdrawn position into a shallow position the second sub-groups of said second main group of control blades at the beginning of said predetermined time period, withdrawing said second sub-groups of said second main group at the end of said predetermined time period and maintaining said second sub-groups of said second main group withdrawn from said core for at least two consecutive time periods immediately subsequent to said predetermined time period. 10. In a nuclear reactor having a core, said core including plural control blades and fuel assemblies with each control blade operationally associated with four fuel bundles of each fuel assembly, sets of said control blades forming discrete control blade groups forming a core pattern including first and second main groups thereof, respectively, symmetrically and asymmetrically arranged about the core, each main group having first and second sub-groups, each sub-group at each control blade location within the core being located alternately in both orthogonally-related X and Y directions in plan view of the core, said first sub-group of said first main group including an operational sub-group; 11. A method according to claim 10 wherein any one control blade of said plural control blades remains withdrawn for at least two consecutive time periods after having been withdrawn from an inserted position. 12. A method according to claim 10, including the further steps of inserting into the core from a withdrawn position into a deep position said first sub-groups of control blades of said first main group at the beginning of a predetermined time period, withdrawing said first sub-groups of control blades of said first main group at the end of said predetermined time period, and maintaining said first sub-groups of said control blades of said first main group withdrawn from said core for at least two consecutive time periods immediately subsequent to said predetermined time period. 13. A method according to claim 12 including the further steps of inserting into said core from a withdrawn position into a shallow position the first operational sub-groups of said first sub-group of said first main group at the beginning of said predetermined time period, withdrawing said first operational sub-groups of said first sub-group of said first main group at the end of said predetermined time period and maintaining said first operational sub-groups of said first sub-group of said first main group withdrawn from said core for at least two consecutive time periods immediately subsequent to said predetermined time period. 14. A method according to claim 13 wherein any one control blade of said plural control blades remains withdrawn for at least two consecutive time periods after having been withdrawn from an inserted position. 15. A method according to claim 10, including the further steps of inserting into the core from a withdrawn position into a shallow position the second sub-group of said second main group of control blades at the beginning of a predetermined time period and maintaining said second sub-groups of said second main group of control blades withdrawn from said core for at least two consecutive time periods, immediately subsequent to said predetermined time period. 16. A method according to claim 10, including the further steps of inserting into the core from a withdrawn position into a deep position the operational sub-groups of said second sub-group of said first main group of control blades at the beginning of a predetermined time period, withdrawing said second operational sub-groups of said second sub-group of said first main group at the end of said predetermined time period and maintaining said second operational sub-groups of said first main group of said control blades withdrawn from said core for at least two consecutive time periods immediately following said predetermined time period. 17. A method according to claim 10, including the further steps of inserting into the core from a withdrawn position into a deep position said second sub-groups of said first main group of control blades at the beginning of a predetermined time period, withdrawing said second sub-groups of said first main group at the end of said predetermined time period and maintaining said second sub-groups of said first main group withdrawn from said core for at least two consecutive time periods immediately subsequent to said predetermined time period. 18. A method according to claim 17 including the further steps of inserting into said core from a withdrawn position into a shallow position the second sub-groups of said second main group of control blades at the beginning of said predetermined time period, withdrawing said second sub-groups of said second main group at the end of said predetermined time period and maintaining said second sub-groups of said second main group withdrawn from said core for at least two consecutive time periods immediately subsequent to said predetermined time period.