Abstract: Exemplary embodiments provide automated nuclear fission reactors and methods for their operation. Exemplary embodiments and aspects include, without limitation, re-use of nuclear fission fuel, alternate fuels and fuel geometries, modular fuel cores, fast fluid cooling, variable burn-up, programmable nuclear thermostats, fast flux irradiation, temperature-driven surface area/volume ratio neutron absorption, low coolant temperature cores, refueling, and the like.

Abstract: A natural circulation boiling water reactor provides to a chimney with a plurality of tubes. That is to say, each of the plurality of tubes partitions the coolant flow path above a core. Thus, unlike the conventional natural circulation boiling water reactor providing the flow path partition wall grid in which the plate members are made integral by welding and coolant flow paths are partitioned, the chimney of the natural circulation boiling water reactor can reduce the number of welded portions because the edges of the four corners of each flow path do not need to be welded. The natural circulation boiling water reactor can avoid removal as a single unit, as in the case of the flow path partition wall grid in the conventional natural circulation boiling water reactor, by detaching each tube. The chimney can be easily detached from the reactor pressure vessel.

Abstract: An electrical discharge machining (EDM) tool and method for removing tack welds on a component in a reactor pressure vessel are disclosed. The tool may include a motor, a housing which engages the component having tack welds, an electrode, positioned in the housing, a first plate, and a second plate attached to the electrode. The second plate actuates to align the electrode to the tack weld, and the electrode is discharged to remove the tack welds from the component.

Abstract: A method of early sensing of water leakage, through chemical concentration monitoring, in a nuclear reactor system using a liquid metal and molten salt, the method including: measuring an electrical conductivity and a mass spectrum of a first channel and a second channel of a heat-related device included in the nuclear reactor system using the liquid metal and the molten salt; calculating a first identification value associated with the water leakage in the heat-related device using the measured electrical conductivity; calculating a second identification value associated with the water leakage in the heat-related device using the measured mass spectrum; and sensing the water leakage by comparing a predetermined reference value and a summed identification value, the summed identification value being the sum of the first identification value and the second identification value.

Abstract: A fast reactor including a reactivity control assembly including a reactor shutdown rod and neutron absorbers, a reactor shutdown rod drive mechanism, and units of neutron absorber drive mechanism. The reactor shutdown rod drive mechanism causes an inner extension tube to fall and release the reactor shutdown rod by a gripper section by turning off the power supply to a holding magnet at the time of scram. When grasping the neutron absorbers, an outer extension shaft is pulled up to allow both of the extension shafts to be inserted. After the outer extension tube gets to a handling head section of the neutron absorber, the outer extension shaft is pushed down to grasp the neutron absorber externally by latch fingers of the gripper section so that the neutron absorber can be moved up and down.

Abstract: Exemplary embodiments provide automated nuclear fission reactors and methods for their operation. Exemplary embodiments and aspects include, without limitation, re-use of nuclear fission fuel, alternate fuels and fuel geometries, modular fuel cores, fast fluid cooling, variable burn-up, programmable nuclear thermostats, fast flux irradiation, temperature-driven surface area/volume ratio neutron absorption, low coolant temperature cores, refueling, and the like.

Abstract: A system for exchanging a control rod drive of a nuclear reactor is provided. The system may include an integrated drive exchange assembly system (IDEAS). The IDEAS may include a trunnion cart attached to a tower assembly. The tower assembly may include an integrated extension carriage assembly. The IDEAS may also include a control rod drive adapter; and a lead cart connected to the trunnion cart assembly.

Abstract: Fuel rods of fuel assemblies of a boiling water reactor are tested for leaks. A plurality of fuel assemblies are each arranged adjacent to one another in a cell of the upper core grid of the boiling water reactor. A hood is placed above a plurality of cells A water sample is taken from each of the cells, and the water samples from a plurality of cells forming a group are combined and tested for the presence of radioactive fission products A plurality of groups are analyzed simultaneously in a number, which number corresponds to the number of groups, of measurement channels. Where a result of a group is positive, the cells of the group are tested separately by the measurement channels. Those fuel assemblies of a cell that is found positive are tested individually outside the hood.

Abstract: In a spent fuel pool of a nuclear power plant, there is provided a system for aligning a nuclear fuel bundle and handling selected fuel rods within the fuel bundle. The bundle includes water rods, full-length and part-length fuel rods extending through a plurality of fuel spacers provided between top and bottom ends of the bundle, each spacer having a plurality of cells accommodating corresponding fuel and water rods. The system includes a bundle alignment system for aligning the fuel rods and water rods, a rod grapple tool to extract selected part-length rods from the bundle, and a fuel rod guide block slidable onto the top end of the bundle for protecting an uppermost fuel spacer of the bundle, and for aligning fuel rods within individual cells of all the fuel spacers in the fuel bundle.

Abstract: A handling method for a natural circulation boiling water reactor having a chimney having cylindrical chimney shell disposed above a core in a reactor pressure vessel, a plurality of square tubes disposed in the chimney shell, and a grid support plate with grid holes supporting and in communication with a lower end portion of the square tubes so that adjacent square tubes are disposed at an interval which exceeds the width of one square tube between them. The method includes steps shifting predetermined ones of the square tubes to the interval between the square tubes, and performing maintenance and inspection of members around a core via the grid holes which appear at positions from which the predetermined square tubes are taken out due to the shift of the predetermined square tubes.

Abstract: A fuel rack for supporting radioactive fuel assemblies in an underwater (or other submerged) environment that reduces the depth required for the pool to effectuate the fuel rack loading procedure. The fuel rack is specially designed to afford lateral loading. In one embodiment, the fuel rack comprises a body structure comprising at least one substantially vertically oriented elongated cell for receiving a nuclear fuel assembly, the body having a top, a bottom and a first lateral side; at least one elongated slot in the first lateral side of the body structure that forms a passageway into the cell through which a vertically oriented fuel assembly can be loaded; and means for supporting a fuel assembly within the cell in a substantially vertical orientation. In another embodiment, the invention is a method of laterally loading a fuel rack that utilizes rotation of the fuel assembly to secure the fuel assembly within its designated cell.

Abstract: A lower and upper end plugs of an annular fuel rod, into and out of which cooling water flows, comprises: a lower end plug including a filter for debris which has a plurality of pins intersecting each other at the proper position of an inner channel main inlet, through-holes into which the pins of the debris filter are fitted, and at least one inner channel auxiliary inlet through which the cooling water flows into a lower inner channel thereof when the inner channel main inlet is blocked by debris, and which has a through-hole shape; and an upper end plug including at least one upper handling groove and hole, into which a fuel rod handling tool is coupled, at a proper position of an inner circumference of the inner channel main outlet in a circumferential direction.

Abstract: A fast reactor 1 controlled with a reflector comprises: a reactor vessel 7 accommodating therein a coolant 5; a reactor core 2 disposed in the reactor vessel 7 and immersed in the coolant 5; and a reflector 4 that vertically moves for adjusting leakage of neutrons generated from the reactor core 2 to control a reactivity of the reactor core 2, the reflector 4 including a neutron reflecting part 4a disposed on an outside of the reactor core 2 in a vertically movable manner, the neutron reflecting part 4a having a neutron reflecting ability higher than that of the coolant 5, and a cavity part 4b positioned above the neutron reflecting part 4a, the cavity part 4b having a neutron reflecting ability lower than that of the coolant 5. The neutron reflecting part 4a is formed of a plurality of metal plates 37 that are stacked on each other. Each of the metal plates 37 has a plurality of coolant channels 36 through which the coolant 5 flows.

Abstract: A nuclear fuel assembly having an instrumentation tube having an insert that centers the in-core instrumentation while permitting bugling or welding of the instrumentation tube wall to a grid strap to obtain a rigid connection there between at any elevation along the instrumentation tube.

Abstract: An alignment system that employs jacking block assemblies and alignment posts around the periphery of the top plate of a nuclear reactor lower internals core shroud to align an upper core plate with the lower internals and the core shroud with the core barrel. The distal ends of the alignment posts are chamfered and are closely received within notches machined in the upper core plate at spaced locations around the outer circumference of the upper core plate. The jacking block assemblies are used to center the core shroud in the core barrel and the alignment posts assure the proper orientation of the upper core plate. The alignment posts may alternately be formed in the upper core plate and the notches may be formed in top plate.

Abstract: An unirradiated nuclear fuel assembly component transport system that includes a clamshell-type inner liner that opens either along its axial dimension or from the top to load and unload the fuel assembly being transported. The exterior dimensions of the liner conform to a generic overpack tubular container that protects the liner from impact loads and fires.