Abstract: A method of fuel bundle consideration in a reactor. The method includes creating or editing bundle groups including fuel bundles.

Abstract: The invention relates to a nuclear power station comprising: at least one high temperature reactor; a storage installation (14) for fuel elements (5); means (32) for transferring the fuel elements (5) between the core (4) and the storage installation (14). According to the invention, the transfer means (32) comprise a tunnel (34) for transferring the fuel elements between the reactor core (4) and the storage installation (14).

Abstract: A method for determining a fresh fuel bundle design for a core of a nuclear reactor may include defining a plurality of inputs including user-defined target conditions for evaluating one or more reference fresh fuel bundle designs for each of N bundle groups, and generating a response surface based on making single rod-type changes in each (i,j) rod location of each bundle of a given reference bundle design being evaluated for each of the N bundle groups. A search algorithm may be iterated to evaluate a given combination of multiple rod-type changes made simultaneously across each of the N bundle groups using the generated response surface to determine an accepted fuel bundle design for each of the N bundle groups that satisfies the user-defined target conditions.

Abstract: A core of a boiling water reactor as a burner type core of the boiling water reactor having a ratio of 3 or more of number of fuel assemblies loaded in the core to number of control rods installed in the nuclear reactor and using an oxide of low enriched uranium having a mean enrichment of the fuel assemblies of 3 wt % to 8 wt % or a mixed oxide having a mean fissile plutonium enrichment of the fuel assemblies of 2 wt % to less than 7 wt %, wherein a mean weight of at least one of uranium and plutonium included in a unit volume of a core region is 2.25 to 3.4 kg/l when load of the fuel assemblies having a burnup of 0 into the core is finished, and a mean thickness of the channel box of the fuel assemblies is 2.10 to 3.55 mm.

Abstract: The apparatus for creating and editing a nuclear reactor core template includes a graphical user interface and a processor controlling the graphical user interface to display a graphical representation of a nuclear reactor core. Via the graphical user interface, the processor provides a user with graphical tools for at least one of assigning fuel bundle categories to fuel bundle positions in the graphical representation and editing assigned fuel bundle categories to the fuel bundle positions in the graphical representation.

Abstract: A method for generating fuel loading data for a core in a nuclear reactor, wherein the core includes an array of fuel locations in the core, the method includes: defining an even cycle bundle shift map of fuel bundles to be shifted to another core location during an even fuel loading cycle; defining an odd cycle shift map of fuel bundles to be shifted to another core location during an odd loading cycle, wherein the odd cycle and even cycle are alternative and successive core refueling cycles; defining a discharge map identifying the another locations to receive the bundles from the locations identified in the even and odd cycle shift maps, and generating shuffling instructions indicating which fuel bundles from a prior fuel cycle are to be shifted to one of the another locations of the core for a subsequent fuel cycle, wherein bundles to be shifted during the even fuel loading cycle are selected from the fuel bundles to be shifted identified in the even cycle bundle shift map and bundles to be shifted during

Abstract: A method has been developed to select fuel rod enrichments for a fuel bundle of a nuclear reactor, the method including: creating an ordered list of fuel rod types in an initial fuel bundle design; perturbing at least a subset of the fuel rod types in the initial fuel bundle design to generate a plurality of perturbed fuel bundle designs; selecting perturbed fuel bundle designs having fuel rods with allowable fuel enrichment types and an allowable average enrichment for the perturbed bundle; determining a difference between each of the selected perturbed fuel bundle design and the initial fuel bundle design, and creating a group of the perturbed fuel bundle design having a difference less than a predetermined threshold difference value.

Abstract: A device and method to move a fuel assembly of a nuclear reactor, wherein the device eliminates the potential for dropping the fuel assembly due to stress corrosion cracking of the upper guide thimble sleeves that attach the top nozzle to guide thimbles.

Abstract: A method of fuel bundle consideration in a reactor. The method includes creating or editing bundle groups including fuel bundles.

Abstract: A method for generating fuel loading data for a core in a nuclear reactor, wherein the core includes an array of fuel locations in the core, the method includes: defining an even cycle bundle shift map of fuel bundles to be shifted to another core location during an even fuel loading cycle; defining an odd cycle shift map of fuel bundles to be shifted to another core location during an odd loading cycle, wherein the odd cycle and even cycle are alternative and successive core refueling cycles; defining a discharge map identifying the another locations to receive the bundles from the locations identified in the even and odd cycle shift maps, and generating shuffling instructions indicating which fuel bundles from a prior fuel cycle are to be shifted to one of the another locations of the core for a subsequent fuel cycle, wherein bundles to be shifted during the even fuel loading cycle are selected from the fuel bundles to be shifted identified in the even cycle bundle shift map and bundles to be shifted during

Abstract: A method, arrangement and computer program is described for generating a database of selectable fresh fuel bundle designs usable in one or more nuclear reactors. In an example, an initial population of candidate fresh fuel bundle designs may be generated and a set of rod-type changes to make to a given candidate in the initial population may be established. A given candidate fresh fuel bundle may be modified by making at least one rod-type change from the set therein. A core loaded with the modified bundle design may be simulated to generate bundle performance outputs. The bundle performance outputs may be ranked based on a plurality of user-input limits. The modified candidate fresh fuel bundle design may be stored, if the bundle performance outputs meet, or are within an accepted margin to, the user-input limits, so as to generate the database.

Abstract: A method and arrangement of determining pin enrichments for a fuel bundle of a nuclear reactor, where a plurality of input parameters and target conditions may be input and enrichment changes, to be made across the fuel bundle, may be calculated using response matrix technology. Fuel bundle pin enrichment data may be output that satisfies the target conditions. The method and arrangement may enable production of fuel bundles having a desired local peaking, exposure peaking and R-factor performance. Consequently, given fuel cycles typically may be loaded and operated such that less fuel may be needed for identical cycle lengths, potentially resulting in improved fuel cycle economics. Additionally, because fuel bundle development may require fewer iterations, there may be a substantial cycle time reduction in the bundle design process, potentially reducing cost and enhancing profitability.

Abstract: A method is for establishing a nuclear reactor core loading pattern (LP) for fuel assemblies and burnable absorbers (BAs). The method establishes an optimum LP through the steps of: a) providing nuclear data representing fuel assemblies and BAs in a nuclear reactor core; b) depleting the nuclear data to form a reference core depletion; c) incorporating the nuclear data into a system of linear equations of a nuclear design quality flux solution method; d) defining the system of linear equations to include constraints which accurately represent the neutron physics of the reactor; employing the equations as a constraint matrix for a MIP solver to find an optimum core pattern solution; f) repeating steps b) through e) updating the constraints and objective functions to satisfy specified engineering requirements and establish an optimum core loading pattern. An algorithm for deriving the system of equations is also disclosed.

Abstract: All possible loading patterns for a nuclear reactor core are searched and optimized for compliance with design constraints. The fuel inventory is divided into a few batches according to coarse levels of reactivity. A recursive enumeration process identifies patterns meeting selected core position constraints, which can be user modified to adjust the search space size. For the batch loading patterns satisfying the constraints, the batches are divided into several smaller batches. A sensitivity matrix linearizing the relationship between fuel assembly position and the depletion model is processed through mixed integer linear programming with branching and bounding to identify an optimal daughter loading pattern. The process is repeated through several levels of batch refinement and selection of optimal daughter patterns, including a level where burnable absorbers are assigned to feed assemblies, until the individual fuel assembly level is reached.

Abstract: An improved method of increasing the power output of an existing nuclear power plant includes increasing the thermal power output of the plant's nuclear island and constructing of an auxiliary BOP to handle the increased thermal power. The thermal power of the nuclear island can be increased such as by increasing the thermal power of the plant's reactor, by replacing the plant's steam generator with one that is more efficient, and by increasing the flow rate and/or change in temperature of a coolant in a secondary cooling loop of the plant. The thermal power of the reactor can be increased such as by replacing existing cylindrical fuel rods with fuel rods having a relatively greater surface area to volume ratio and/or by increasing the flow rate and/or the change in temperature of a coolant of a primary cooling loop. The auxiliary BOP can be constructed while the plant is in operation, and can then be connected with the nuclear island during a maintenance operation on the reactor.

Abstract: A method and apparatus is disclosed for smoothly inserting a fuel rod loader through the skeleton of a fuel cell and then for pulling an attached fuel rod into the fuel rod skeleton while keeping the fuel rod under constant tension and preventing the bowing of the fuel rod. The pulling mechanism comprises a smooth collet with a smooth bullet end cap for guiding the puller mechanism into and through the skeleton where the bullet end cap is removed and the fuel rod is attached with a unique ball and slide mechanism actuated by a long puller rod that grabs the end of the fuel rod by a forward motion of the puller rod and is easily removed from the fuel rod by reversing this motion once the fuel rod is in place.

Abstract: A reactor core (104) includes fuel assemblies (202) arranged in a loading pattern (1100) in response to corresponding power levels of the fuel assemblies (202). A crud deposition model (412) is used to predict crud deposition on the fuel assemblies (202) and fuel pins (300) within the fuel assemblies (202). The prediction of crud deposition enables generation of the loading pattern (1100) and design of lattice structures (1600) for the fuel assemblies (202) that results in the reduction of total crud deposition in the reactor core (104) and causes a substantially uniform crud deposition on the fuel assemblies (202) of the reactor core (104).

Abstract: According to the method, a reactor core is shut down during the operation cycle. One or more fuel bundles of the reactor core are then moved to new positions within the reactor core to increase a total energy, output of the reactor core as compared to continuing operation of the reactor core without the shutting down and moving steps.

Abstract: All possible loading patterns for a nuclear reactor core are searched and optimized for compliance with design constraints. The fuel inventory is divided into a few batches according to coarse levels of reactivity. A recursive enumeration process identifies patterns meeting selected core position constraints, which can be user modified to adjust the search space size. For the batch loading patterns satisfying the constraints, the batches are divided into several smaller batches. A sensitivity matrix linearizing the relationship between fuel assembly position and the depletion model is processed through mixed integer linear programming with branching and bounding to identify an optimal daughter loading pattern. The process is repeated through several levels of batch refinement and selection of optimal daughter patterns, including a level where burnable absorbers are assigned to feed assemblies, until the individual fuel assembly level is reached.

Abstract: A method of operating a nuclear reactor reduces the number of reload fuels to be loaded into the nuclear reactor in the second and the following operation cycles. The nuclear reactor has a reactor core in which a plurality of reload fuel assemblies respectively having different infinite multiplication factors are arranged. The method operates the nuclear reactor with control rods inserted in control cells each comprising four reload fuel assemblies having relatively large infinite multiplication factors among the plurality of reload fuel assemblies for a period longer than half of a period of an operation cycle.

Abstract: A sleeve assembly for refurbishing a fuel rack having cells in which fresh or spent nuclear fuel assemblies may be stored, in which the cells have elongate rack walls extending from a rack base plate and the rack base plate has flow holes communicating with the cells. The sleeve has at least one elongate wall extending from the topside of a sleeve base having an opposed bottom side. The sleeve base has a flow hole extending therethrough that communicates with one of the rack base plate flow holes. A pin assembly disposed in the sleeve base flow hole has resilient tabs extending beyond the bottom side of the sleeve base for extending into a rack base plate flow hole and resiliently engaging the rack base plate when the sleeve assembly is installed in one of the cells. The pin assembly resists horizontal and vertical movements of the sleeve assembly, permits water flow into the cell and permits sleeve assembly removal tools and inspection devices to access the pin assembly.

Abstract: A Critical Channel Power (CCP) enhancement system is provided for a pressurized fuel-channel-type water-cooled nuclear reactor of the type adapted to be refuelled on-line by the insertion and removal of fuel bundles onto and from of a plurality of said fuel channel assemblies, each of said fuel channel assemblies. A means is provided for interlocking fuel bundles into pairs having their fuel elements aligned, thereby lowering the hydraulic resistance in the fuel channel and enhancing CCP. The means for interlocking prevents misalignment of the paired bundles during their residence time inside the reactor due to continuous rocking and vibration of the fuel bundles exposed to very high coolant mass flow rate and misalignment due to axial separation of bundles impacting upon one another during fuelling operations.

Abstract: In order to use up a stockpile of weapons-grade plutonium, the plutonium is converted into a mixed oxide (MOX) fuel form wherein it can be disposed in a plurality of different fuel assembly types. Depending on the equilibrium cycle that is required, a predetermined number of one or more of the fuel assembly types are selected and arranged in the core of the reactor in accordance with a selected loading schedule. Each of the fuel assemblies is designed to produce different combustion characteristics whereby the appropriate selection and disposition in the core enables the resulting equilibrium cycle to closely resemble that which is produced using urania fuel. The arrangement of the MOX rods and burnable absorber rods within each of the fuel assemblies, in combination with a selective control of the amount of plutonium which is contained in each of the MOX rods, is used to tailor the combustion characteristics of the assembly.

Abstract: In order to use up a stockpile of weapons-grade plutonium, the plutonium is converted into a mixed oxide (MOX) fuel form wherein it can be disposed in a plurality of different fuel assembly types. Depending on the equilibrium cycle that is required, a predetermined number of one or more of the fuel assembly types are selected and arranged in the core of the reactor in accordance with a selected loading schedule. Each of the fuel assemblies is designed to produce different combustion characteristics whereby the appropriate selection and disposition in the core enables the resulting equilibrium cycle to closely resemble that which is produced using urania fuel. The arrangement of the MOX rods and burnable absorber rods within each of the fuel assemblies, in combination with a selective control of the amount of plutonium which is contained in each of the MOX rods, is used to tailor the combustion. characteristics of the assembly.

Abstract: Several unit loading patterns are arranged in the central area of an initial core to which the present invention is applied. The unit loading pattern is composed of one square-shaped unit cell and four cross-shaped control rods 3 which surround the unit cell. The unit cell is composed of one low enrichment fuel assembly 7, two high enrichment fuel assemblies 8 and one high enrichment fuel assembly 9. The low enrichment fuel assemblies 7 of each unit loading pattern adjoin each other and are arranged to constitute the first control cell 2a being square-shaped. The high enrichment fuel assemblies 9, obliquely adjoining the low enrichment fuel assembly 7 in each unit loading pattern, adjoin each other and are arranged to constitute the second control cell 2b being square-shaped.

Abstract: Seed-blanket type nuclear reactor cores are employed to burn thorium fuel with conventional reactor fuels, including nonproliferative enriched uranium, and weapons or reactor grade plutonium. In a first embodiment, the core is completely nonproliferative in that neither the reactor fuel, nor the generated waste material, can be used to manufacture nuclear weapons. In a second embodiment of the invention, the core is employed to burn large amounts of weapons grade plutonium with the thorium, and provides a convenient mechanism by which stockpiled weapons grade plutonium can be destroyed and converted into electrical energy. The cores of both embodiments are comprised of a plurality of seed-blanket unit fuel assemblies which have centrally located seed regions that are surrounded by annular blanket regions. The seed regions contain the uranium or plutonium fuel rods, while the blanket regions contain thorium fuel rods.

Abstract: In an arrangement of an initial core, the core is loaded with 572 high enrichment fuel assemblies H with 4.2 wt % average enrichment and 300 low enrichment fuel assemblies L with 1.5 wt % average enrichment. The average enrichment of the core is about 3.3 wt %. In this core, only the low enrichment fuel assemblies are loaded into the most outer position of the core and the high enrichment fuel assemblies are loaded into an area other than the most outer position. In this arrangement, the average enrichment of reload fuel assemblies is 3.7 wt %.

Abstract: The present invention, in one aspect, is a method for identifying an optimum core loading arrangement. The method generally has an initialization phase and a running, or search, phase. In the initialization phase, an initial core loading arrangement is identified based on the relative reactivity levels of the bundles to be loaded and the reactor core locations. Once the initial core loading arrangement is identified, such arrangement is then optimized, within the defined constraints, in the running phase. More specifically, in the running phase, each core location is analyzed to determine whether such core location reactivity level can be changed from the initial reactivity level to either satisfy a constraint or optimize cycle energy, or both.

Abstract: In order to use up a stockpile of weapons-grade plutonium, the plutonium is converted into a mixed oxide (MOX) fuel form wherein it can be disposed in a plurality of different fuel assembly types. Depending on the equilibrium cycle that is required, a predetermined number of one or more of the fuel assembly types are selected and arranged in the core of the reactor in accordance with a selected loading schedule. Each of the fuel assemblies is designed to produce different combustion characteristics whereby the appropriate selection and disposition in the core enables the resulting equilibrium cycle to closely resemble that which is produced using urania fuel. The arrangement of the MOX rods and burnable absorber rods within each of the fuel assemblies, in combination with a selective control of the amount of plutonium which is contained in each of the MOX rods, is used to tailor the combustion characteristics of the assembly.

Abstract: A method and system for identifying the maximum adverse impact of a mislocated nuclear fuel bundle placement in an nuclear core loading arrangement is presented. The method generally has an initialization phase and a "swap" case evaluation, or "search," phase. In the initialization phase, base conditions for a selected core loading arrangement are determined and parameters for exploring the mislocated fuel bundle loading error problem are set up. In the search phase, the core loading arrangement design space is explored for many combinations of mislocated fuel bundle pairs in order to find a mislocated fuel bundle pair that yields the most limiting core state. A computer system is used to execute specific program routines that simulate the operating conditions of a reactor having mislocation errors involving fuel bundle pairs in a core loading arrangement.

Abstract: In a fuel loading method of the present invention, a nuclear reactor is operated up to the second cycle without exchanging the fuel. Low-enrichment fuel is discharged from a core at the end of the second cycle and at the end of the third cycle. Moreover, high-enrichment fuel with an average enrichment higher than that of replacement fuel is discharged from the core at the end of the third cycle and reloaded into the core at the end of the fifth cycle.According to the present invention, because the high-enrichment fuel discharged from the core at the end of the third cycle normally has a high enrichment, a short combustion period, and a low burnup compared to the replacement fuel burned for 4 to 5 cycles, a lot of fissionable material are left in the high-enrichment fuel. By reloading the high-enrichment fuel to the core after one cycle or more passes, it is possible to greatly increase the discharge exposure of initially loaded fuel.

Abstract: In reactor water control for a BWR power plant during an operation cycle after loading new fuel rods in the BWR power plant, an operation is performed which accelerates deposition of crud on the fuel rods until the deposition amount of the crud on the fuel rods reaches a predetermined target value within the operation cycle concerned. After the deposition amount of the crud has reached the predetermined target value, the crud deposition accelerating operation is terminated, whereby even when loading new fuel rods such as Zr liner type fuel rods having a surface on which metal ion deposition has been difficult, radioactivity in the reactor water is efficiently reduced.

Abstract: The present invention relates to method of fueling and operating a nuclear reactor core. Fueling the nuclear reactor core for a power operation cycle includes the steps of designating a central core region, a buckled core region and a peripheral core region, placing at least two fuel assemblies of relatively high reactivity in the fuel cells in the central core region and placing fuel assemblies of relatively low reactivity in the cells in the peripheral core region.

Abstract: In an initial core constituted by various kinds of fuel assemblies having a different average enrichment of uranium 235 four fuel assemblies having the lowest average enrichment constitute a square shaped cell. Three fuel assemblies having the highest average enrichment constitute an L-shaped cell, and the L-shaped cell is arranged at corners of the square shaped cells, whereby each assembly of the L-shaped cell adjoins a square shaped cell. The ratio of the number of assemblies of the L-shaped cell to the total number of fuel assemblies in the core is 10% or more.

Abstract: A fuel assembly has part length and full length fuel rods, and a pair of large-diameter water rods which occupy an area which can accommodate 7 fuel rods. Natural uranium regions are provided in the upper and lower end portions of the effective fuel zone of the fuel assembly. An intermediate region between these upper and lower natural uranium regions provides an enriched uranium region which has three axial sections: an upper section, a middle section and a lower section. The middle section has the highest average enrichment, the lower section has the medium average enrichment and the upper section has the smallest average enrichment. The difference in the average enrichment between the middle section and the lower section is smaller than that between the middle section and the upper section. The upper section has a lower concentration of burnable poison than other sections of the enriched uranium region.

Abstract: A nuclear reactor of boiling water type has a reactor core including a plurality of vertical fuel assemblies (30, 30a) of substantially square cross section arranged in a lattice, with each fuel assembly included in two rows of fuel assemblies, perpendicular to each other and separated by intermediate water gaps (27a, 27b). Each fuel assembly comprises two vertical perpendicular sides, each side facing a water gap which has a larger width than a water gap toward which the opposite two vertical perpendicular sides face. After an operating cycle for the reactor of at least two years, the majority of the fuel assemblies used during the completed operating cycle, which are located in an edge zone (25) furthest out in the core, are turned 180 degrees around the vertical center line of the respective fuel assembly, and the turned fuel assemblies are used for a following operating cycle of the reactor.

Abstract: In a fuel loading method for a reactor core made up by high burn-up fuel, fuel assemblies loaded in a circumferential zone of the core are shuffled between two layers of the circumferential zone until residing in the core for two cycles and, after residing for two cycles, are moved to the fourth layer of the circumferential zone from an outermost layer of the core, thereby reducing the difference in exposure due to a different radial power level in the vicinity of the core boundary. Those fuel assemblies are moved to control cells in a central zone of the core after residing in the circumferential zone for three cycles, and also such fuel assemblies as having resided in the central zone for three cycles are moved to the core outermost layer, thereby reducing the difference in exposure between the fuel assemblies having resided in the central zone and the fuel assemblies having resided in the circumferential zone due to different power levels in the central and circumferential zones.

Abstract: In combination with a boiling water nuclear reactor core undergoing a reload, an improved core reload and process of reloading is disclosed. The core reload consists of fuel bundles having differing design margins to critical power and linear heat generation rate. Specifically, a first part of the core reload is selected from fuel bundles having relatively high critical power margin and relatively lower linear heat generation margin. A second part of the core reload is selected from fuel bundles having relatively high linear heat generation margin and relatively low critical power margin. Distribution of the reload fuel bundles throughout the reactor core occurs as a function of critical power margin and linear heat generation rate margin. Specifically, fuel bundles having the high critical power margin are placed in selected intervals to the central portion of the cylindrical core. Fuel bundles having high linear heat generation margin are placed in the peripheral region of the core.

Abstract: A core construction for boiling water nuclear reactor in which a multiplicity of core units each having four fuel assemblies disposed in a square pattern adjacent to a control rod are arranged to form a reactor core, wherein the reactor core comprises control cells comprising four fuel assemblies which have been in the core more than three cyclic periods. The fuel assemblies located in the outer peripheral portion of the core are fuel assemblies which have been in the core more than three cyclic periods. Most of the core units comprise four fuel assemblies of first-, second-, third- or fourth-burning cyclic periods. The core is rotationally symmetric by 90 degrees. The core can be divided into four identical 1/4 cores by two vertical planes passing axial center lines of the core. Each of the 1/4 cores is substantially mirror symmetric about a plane passing the axial center line of the core.

Abstract: Fuel management in a boiling-water nuclear reactor involves arranging fuel bundles in upper and lower matrices of the reactor core. During a refueling operation, some bundles in the upper matrix are removed and retired, while fresh bundles are inserted in the lower matrix and some bundles originally in the lower matrix are transferred to the upper matrix. In the transfer, fuel bundles are inverted so that included fuel rods in the lower matrix have their plenums oriented downward, while fuel rods in the upper matrix have their plenums oriented upward. This method provides greater flexibility in repositioning fuel bundles for longer burnups and lower high-level waste. In particular, problems with axial spectral variations in neutron flux can be compensated for using the disclosed refueling procedure.

Abstract: In accordance with the present invention, a nuclear reactor with a recirculating heat transfer fluid has a bi-level core which provides enhanced flexibility in fuel arrangement. The bi-level core includes two sets of fuel units, one set arranged on a first level, the other set arranged on a second level. Preferably, fuel units of the second level are arranged in vertical alignment with fuel units of the first level. This permits a fuel unit of the first level to be accessed by removing only the adjacent fuel unit of the second level. During refueling operations, fuel units can be shifted from one level to the other, providing additional flexibility in arranging units at various stages of burnup. Preferably, fuel units of the first level are inverted relative to the fuel units of the second level.

Abstract: Fresh fuel bundles are inserted into core locations with small coolant flow orifices, while mid-life fuel bundles are inserted into core locatiosn with large coolant flow locations. Thus, fissile fuel production is promoted at the expense of fissioning early in a bundle lifetime, increasing the effective quantity of fuel available for energy production. Moreover, fissioning is promoted at the expense of conversion later in the bundle lifetime to enhance reactivity of the remaining fissile material and to minimize the further production of fissile fuel. The net result is longer fuel lifetimes and reduced radioactive waste.

Abstract: Fuel assemblies of a boiling-water nuclear reactor are inverted during refueling methods. Assemblies burned in a first orientation are subjected to greater burnup near their bottoms and greater conversion of fertile fuel to fissile fuel near their tops. Inverting the assemblies promotes burnup of the actinide products from the conversion of the last cycle. Thus, the procedure greater energy production efficiency and reduced actinide radioactive waste are achieved. One inverted fuel assemblies can be removed for disposal. Alternatively, they can be reinverted to burnup actinide fissile fuel generated at the bottom (while it was downstream of the top) during the second operating cycle. Further inversions are provided for, but the major gains occur during the first and second inversions.

Abstract: A core of boiling water reactor is divided into a central region and a peripheral region surrounding it in the radial direction thereof. The loading fraction of new first fuel assemblies containing burnable poison and loaded in the central region is greater than the loading fraction of the new first fuel assemblies loaded in the peripheral region. The loading fraction of second fuel assemblies loaded in the central region of the core and operating in a second operation cycle is smaller than the loading fraction of the second fuel assemblies loaded in the peripheral region of the core and operating in the second operation cycle. The second fuel assemblies contain no burnable poison. In such a core, the reactivity of the peripheral region is greater than that of the central region in the beginning of an operation cycle. Contrary, the reactivity of the central region is greater than that of the peripheral region in the end of an operation cycle.

Abstract: The present invention relates to nuclear reactors and more specifically to a fuel bundle arrangement for a boiling water nuclear reactor in which so-called mixed oxide fuels including plutonium and uranium are utilized in a nuclear fuel bundle together with a burnable absorber such as gadolinium to optimize the reaction of a nuclear fuel bundle.

Abstract: A control rod cluster assembly of a nuclear reactor is repeatedly repositioned in a guide tube assembly above a fuel assembly in the reactor core in single steps at separate times during a single fuel cycle. For instance, the single-step repositioning can be repeated once every month or every four months in a twelve month fuel cycle.

Abstract: The reactor core is divided into a central region and a surrounding outer region in the radial direction. First fresh fuel unirradiated assemblies newly loaded onto the outer region contain a fissible material in amounts less than that of the fissible material of second fresh unirradiated fuel assemblies newly loaded onto the central region. If the amount of the fissible material in the upper region of the first fuel assembly is denoted by a, the amount of the fissible material in the lower region of the first fuel assembly by b, the amount of the fissible material in the upper region of the second fuel assembly by c, and the amount of the fissible material in the lower region of the second fuel assembly by d, then a relationship a/b<c/d is satisfied. The reactor core provides sufficient thermal margin and improved cold shutdown margin.

Abstract: In a light water moderation type nuclear reactor with the once-through method, the reactor core is divided into a central area and a peripheral area by a partition member, a first fuel assembly is arranged in the central area (high conversion area) and a second fuel assembly is arranged in the peripheral area. The ratio (r.sub.H/U) of the number of hydrogen atoms to that of uranium atoms in the central area is smaller than that of the ratio in the peripheral area and the second fuel assembly in the peripheral area is formed of fuel rods of the first fuel assembly having been previously burned in the central area and moved into the peripheral area. The plutonium production increases and uranium consumption is reduced during the first half of the lifetime of the fuel rods in the high conversion area with the take-up burn up increasing during the second half of the lifetime of the fuel rods in the burner area.

Abstract: Demand for refueling of a liquid metal fast nuclear reactor having a life of 30 years is eliminated or reduced to intervals of at least 10 years by operating the reactor at a low linear-power density, typically 2.5 kw/ft of fuel rod, rather than 7.5 or 15 kw/ft, which is the prior art practice. So that power of the same magnitude as for prior art reactors is produced, the volume of the core is increased. In addition, the height of the core and it diameter are dimensioned so that the ratio of the height to the diameter approximates 1 to the extent practicable considering the requirement of control and that the pressure drop in the coolant shall not be excessive. The surface area of a cylinder of given volume is a minimum if the ratio of the height to the diameter is 1. By minimizing the surface area, the leakage of neutrons is reduced.

Abstract: The core of a pressurized water nuclear reactor is partly formed from dismantlable assemblies (10), whereof the rods contain mixed UO.sub.2 -PuO.sub.2 oxide pellets, said assemblies (10) being subdivided into concentric zones (12,14,16) with a plutonium concentration decreasing from the inside to the outside. At the end of each irradiation cycle, the rods (C.sub.3) located in peripheral zone (16) are discharged and the rods (C.sub.2,C.sub.1) located in the other zones (12,14) are transferred towards the outside of assembly (10) into zone (14,16) adjacent to that which they previously occupied. New rods (C.sub.4) with a single enrichment are then introduced into the thus freed central zone (12).