Patent Number: 052672913
Section: claims

1. In a fuel bundle for a boiling water nuclear reactor, including a plurality of side-by-side vertically disposed sealed nuclear fuel rods, said fuel rods arrayed in a square section, a lower tie plate for supporting said fuel rods and permitting the entrance of water moderator to said fuel bundle between said fuel rods, an upper tie plate with at least some of the fuel rods fastened thereto and permitting the exit of water and generated steam from said fuel bundle, a plurality of vertically separated spacers surrounding each said fuel rod at the elevation of said spacer to hold said fuel rods in designed spaced apart relation as a unitary mass at the elevation of said spacers, each said spacer including a peripheral band having four sides, each of said sides corresponding to one of said sides of said square section, and a channel surrounding said lower tie plate, said upper tie plate and said fuel rods and spacers there between, said channel defining a complimentary and larger square section with respect to said square section of said square array of fuel rods, said channel during operation of said reactor defining a flow boundary between a core bypass region containing water moderator on the outside and a steam generating flow path through said fuel bundle between said tie plates on the inside, the improvement to the peripheral band of at least one spacer for maintaining required spatial separation between said fuel rods and channel for neutron moderation and steam generation comprising: two first adjacent spacer sides defining at least two full dimension outward protrusions occupying the entire interval necessary to maintain the fuel rods adjacent all four sides at their full optimal spacing from the interior channel walls whereby said fuel rods adjoining said two adjacent spacer sides are maintained at an optimal spacing from said channel wall to assure optimum neutron moderation and moderator flow around said fuel rods to maintain optimum critical power on fuel rods adjacent said channel;  two second and remaining adjacent spacer sides defining lesser dimension outward protrusions occupying a sufficient and lesser interval to prevent inadvertent closing of the fuel rods adjacent said second and remaining adjacent spacer sides to the channel sides beyond said lesser interval, said lesser interval chosen to provide the peripheral fuel rods adjacent said second and remaining spacer sides with adequate clearance from said channel wall to maintain a safe level of neutron moderation and avoid a worst case critical power limitation; and  spring means on said two second and remaining adjacent sides of the peripheral spacer band acting on the channel wall given sufficient force to bias the fuel rod matrix at the spacer away from the channel wall at said two second and remaining adjacent sides to register the full dimension outward protrusions at the first and adjacent spacer sides to the channel wall at the opposite sides of the spacer whereby said fuel rods adjoining said all spacer sides are maintained at an optimal spacing from said channel wall to assure optimum neutron moderation and moderator flow around said fuel rods to maintain optimum critical power on fuel rods adjacent said channel.  a plurality of side-by-side sealed vertically disposed nuclear fuel rods, said fuel rods arrayed in a square section;  a lower tie plate for supporting said fuel rods and permitting the entrance of water moderator to said fuel bundle between said fuel rods;  an upper tie plate with at least some of the fuel rods fastened thereto and permitting the exit of water and generated steam from said fuel bundle;  a plurality of vertically separated spacers surrounding each said fuel rod at the elevation of said spacer to hold said fuel rods in designed spaced apart relation as a unitary mass at the elevation of said spacers, each said spacer including a peripheral band having four adjacent sides; and,  a channel surrounding said lower tie plate, said upper tie plate and said fuel rods and spacers there between, said channel defining a complimentary and larger square section with respect to said square section of said square array of fuel rods, said channel during operation of said reactor defining a flow boundary between a core bypass region containing water moderator on the outside and a steam generating flow path through said fuel bundle between said tie plates on the inside;  the peripheral band of at least one spacer having two first adjacent spacer sides defining at least two full dimension outward protrusions occupying the entire interval necessary to maintain the fuel rods adjacent all four sides at their full optimal spacing from the interior channel walls whereby said fuel rods adjoining said two adjacent spacer sides are maintained at an optimal spacing from said channel wall to assure optimum neutron moderation and moderator flow around said fuel rods to maintain optimum critical power on fuel rods adjacent said channel;  said peripheral band further including two second and remaining adjacent spacer sides defining lesser dimension outward protrusions occupying a sufficient and lesser interval to prevent inadvertent closing of the fuel rods adjacent said second and remaining adjacent spacer sides to the channel sides beyond said lesser interval, said lesser interval chosen to provide the peripheral fuel rods adjacent said second and remaining spacer sides with adequate clearance from said channel wall to maintain a safe level of neutron moderation and avoid a worst case critical power limitation; and,  spring means on said two second and remaining adjacent sides of the peripheral spacer band acting on the channel wall given sufficient force to bias the fuel rod matrix at the spacer away from the channel wall at said two second and remaining adjacent sides to register the full dimension outward protrusions at the first and adjacent spacer sides to the channel wall at the opposite sides of the spacer whereby said fuel rods adjoining said all spacer sides are maintained at an optimal spacing from said channel wall to assure optimum neutron moderation and moderator flow around said fuel rods to maintain optimum critical power on fuel rods adjacent said channel.  a spacer body for placement at a selected elevation between said tie plates, said spacer body for defining about each said fuel rod at a spacer position between said tie plates separation between said fuel rods for maintaining said fuel rods in designed side-by-side relation;  each said spacer including a square sectioned peripheral band having four sides;  two first adjacent spacer sides defining at least two full dimension outward protrusions occupying the entire interval necessary to maintain the fuel rods adjacent all four sides at their full optimal spacing from the interior channel walls whereby said fuel rods adjoining said two adjacent spacer sides are maintained at an optimal spacing from said channel wall to assure optimum neutron moderation and moderator flow around said fuel rods to maintain optimum critical power on fuel rods adjacent said channel;  two second and remaining adjacent spacer sides defining lesser dimension outward protrusions occupying a sufficient and lesser interval to prevent inadvertent closing of the fuel rods adjacent said second and remaining adjacent spacer sides to the channel sides beyond said lesser interval, said lesser interval chosen to provide the peripheral fuel rods adjacent said second and remaining spacer sides with adequate clearance from said channel wall to maintain a safe level of neutron moderation and avoid a worst case critical power limitation; and  spring means on said two second and remaining adjacent sides of the peripheral spacer band acting on the channel given sufficient force to bias the fuel rod matrix at the spacer away from the channel wall at said two second and remaining adjacent sides to register the full dimension outward protrusions at the first and adjacent spacer sides to the channel wall at the opposite sides of the spacer whereby said fuel rods adjoining said all spacer sides are maintained at an optimal spacing from said channel wall to assure optimum neutron moderation and moderator flow around said fuel rods to maintain optimum critical power on fuel rods adjacent said channel. 2. The fuel bundle of claim 1 wherein said spring means includes a leaf spring. 3. The fuel bundle of claim 2 and wherein said leaf spring is placed adjacent the corner of said channel. 4. The fuel bundle of claim 1 and wherein each peripheral band at said remaining sides includes paired spring means. 5. A fuel bundle for a boiling water nuclear reactor, comprising: 6. The fuel bundle of claim 5 and wherein said spring means includes a leaf spring. 7. The fuel bundle of claim 6 and wherein said leaf spring is placed adjacent the corner of said channel. 8. In a spacer for fuel bundle for a boiling water nuclear reactor fuel bundle, said fuel bundle including a plurality of side-by-side vertically disposed sealed nuclear fuel rods, said fuel rods arrayed in a square section, a lower tie plate for supporting said fuel rods and permitting the entrance of water moderator to said fuel bundle between said fuel rods, and upper tie plate with at least some of the fuel rods fastened thereto and permitting the exit of water and generated steam from said fuel bundle, a channel surrounding said lower tie plate, said upper tie plate and said fuel rods and spacers there between, said channel defining a complimentary and larger square section with respect to said square section of said square array of fuel rods, said channel during operation of said reactor defining a flow boundary between a core bypass region containing water moderator on the outside and a steam generating flow path through said fuel bundle between said tie plates on the inside, said spacer comprising: 9. The fuel bundle of claim 8 and wherein each peripheral band at said remaining sides includes paired spring means.