Patent Number: 051981831
Section: summary

FIELD OF THE INVENTION The present invention relates generally to an apparatus and method for close packing of nuclear fuel assemblies. More specifically, the present invention relates to placement of at least one neutron absorbing plate between columns of nuclear fuel rods within a nuclear fuel assembly. BACKGROUND OF THE INVENTION In the nuclear power industry, storage and transportation of nuclear fuel assemblies is complicated by having to "nuclearly" isolate portions of nuclear fuel from other portions in order to avoid conditions of criticality which could lead to an uncontrolled nuclear chain reaction. Nuclear fuel assemblies are made up of fuel rods supported in a rack structure and separated with grid spacers. Interspersed within the fuel rod matrix are control rod guide tubes. Nuclear isolation in storage and transportation is presently done in three ways; (1) placing neutron absorbing material between nuclear fuel assemblies, or by placing nuclear fuel assemblies into neutron absorbing baskets, (2) dismantling the nuclear fuel assembly and consolidating fuel rods into close packed arrays, and (3) relying on "burnup" or depletion of fuel to allow close packing of nuclear fuel assemblies without interposing neutron absorbing material. Each method has inherent disadvantages. Placement of neutron absorbing material between nuclear fuel assemblies or placement of nuclear fuel assemblies into baskets increases the volume required for storage or transportation of multiple nuclear fuel assemblies. Moreover, use of a basket imposes a fixed amount of neutron absorbing material whether the assembly is fresh or spent. Consolidation of nuclear fuel assemblies is limited because the operation must be done under water such as in a spent fuel pool. Relying on burnup precludes close storage or transportation of new or partially spent nuclear fuel assemblies. In addition, there is a risk that a spent nuclear fuel assembly is not as "spent" as expected. It would be advantageous to closely pack nuclear fuel assemblies by eliminating neutron absorbing material placed between nuclear fuel assemblies, without having to consolidate them and using only enough neutron absorbing material appropriate for the status of a particular nuclear fuel assembly. The present invention offers just such a solution. SUMMARY OF THE INVENTION The present invention relates generally to an apparatus and method for close packing of nuclear fuel assemblies. More specifically, the present invention relates to placement of at least one neutron absorbing plate between columns of nuclear fuel rods within a nuclear fuel assembly. The apparatus of the present invention is a plate of neutron absorbing material. The plate may have a releasable locking feature permitting the plate to be secured within a nuclear fuel assembly between nuclear fuel rods during storage or transportation, then removed for further use or destruction of the nuclear fuel assembly. The method of the present invention has the step of placing a plate of neutron absorbing material between nuclear fuel rods within a nuclear fuel assembly, preferably between the two outermost columns of nuclear fuel rods. Additionally, the plate may be releasably locked in place. The subject matter of the present invention is particularly pointed out and distinctly claimed in the concluding portion of this specification. However, both the organization and method of operation, together with further advantages and objects thereof, may best be understood by reference to the following description taken in connection with accompanying drawings wherein like reference characters refer to like elements.