Abstract: A method of producing a light water reactor fuel assembly may include: setting conditions at least concerning an operation cycle period and burnup; setting an initial enrichment of enriched uranium; calculating excess reactivity of a light water reactor core where light water reactor fuel assemblies including the enriched uranium are burned until an end stage of a final operation cycle; determining whether a condition where excess reactivity at an end of a first operation cycle in the burnup calculation step is close to a predetermined positive value is true or not; and returning to the setting of the initial enrichment, when it is determined at the determining that the situation is not true, or deciding an enrichment of the enriched uranium when it is determined that the situation is true.

Abstract: According to embodiments, a light water reactor uranium fuel assembly is capable of reducing heating values of both Am-241 and Cm-244, to reduce the amount of generated vitrified waste without using fast reactors. The light water reactor uranium fuel assembly is a light water reactor uranium fuel assembly to be used in a nuclear fuel cycle that extracts. An americium isotope is extracted at the time of reprocessing of spent fuel to be added to a fuel, in which a weight fraction W (unit: wt %) of americium 241 to be added to a fuel heavy metal is in ranges of W<?0.006e2+0.12e?0.43 (enrichment: 5 wt % or more), W<?0.000356e+0.00357 (enrichment: 4.2 wt % or more and less than 5.0 wt %) with respect to an average enrichment of uranium 235 e (unit: wt %) of the fuel assembly.

Abstract: A nuclear reactor comprising: a moderator including a metal hydride; and a nuclear fuel in which europium is added as an additive to a main nuclear fuel material. Thus, the nuclear reactor can be kept in the subcritical state even under the state where all the control devices are pulled out before startup.

Abstract: A method of producing a light water reactor fuel assembly may include: setting conditions at least concerning an operation cycle period and burnup; setting an initial enrichment of enriched uranium; calculating excess reactivity of a light water reactor core where light water reactor fuel assemblies including the enriched uranium are burned until an end stage of a final operation cycle; determining whether a condition where excess reactivity at an end of a first operation cycle in the burnup calculation step is close to a predetermined positive value is true or not; and returning to the setting of the initial enrichment, when it is determined at the determining that the situation is not true, or deciding an enrichment of the enriched uranium when it is determined that the situation is true.

Abstract: According to embodiments, a light water reactor uranium fuel assembly is capable of reducing heating values of both Am-241 and Cm-244, to reduce the amount of generated vitrified waste without using fast reactors. The light water reactor uranium fuel assembly is a light water reactor uranium fuel assembly to be used in a nuclear fuel cycle that extracts. An americium isotope is extracted at the time of reprocessing of spent fuel to be added to a fuel, in which a weight fraction W (unit: wt %) of americium 241 to be added to a fuel heavy metal is in ranges of W<?0.006e2+0.12e?0.43 (enrichment: 5 wt % or more), W<?0.000356e+0.00357 (enrichment: 4.2 wt % or more and less than 5.0 wt %) with respect to an average enrichment of uranium 235 e (unit: wt %) of the fuel assembly.

Abstract: A thermal-neutron reactor core includes: a solid moderator expanding to a lengthwise direction; a fuel in the moderator, parallel to the lengthwise direction of the moderator, the fuel containing a fissile material; a cooling tube parallel to the lengthwise direction of the moderator; and a plurality of kinds of burnable poison included in the fuel. The may contain a metal hydride. Furthermore, the plurality of kinds of burnable poison may include one burnable poison containing a concentration of one particular isotope of that one burnable poison.

Abstract: According to an embodiment, a design method for a light-water reactor fuel assembly comprises: accumulating a determined fuel data, showing that each of a combination of p·n/N and e is feasible as the core or not, wherein N is a number of the fuel rods in the fuel assembly, n is a number of the fuel rods containing the burnable poison, p is a ratio wt % of the burnable poison in the fuel, and e is an enrichment wt % of the uranium 235 contained in the fuel assembly; formulating a criterion formula which determines whether a combination of p·n/N and e is feasible as a core or not and is formulated based on the determined fuel data; and determining whether a temporarily set composition of the fuel assembly is approved as a core or not based on the criterion formula.

Abstract: A nuclear reactor comprising: a moderator including a metal hydride; and a nuclear fuel in which europium is added as an additive to a main nuclear fuel material. Thus, the nuclear reactor can be kept in the subcritical state even under the state where all the control devices are pulled out before startup.

Abstract: A heat pipe, includes; an outer tube including first and second ends, the first end closed air tight; a box connected to the second end, a cross-sectional area of the box perpendicular to the outer tube central axis is larger than a cross-sectional area of the outer tube perpendicular to its axis; an inner tube positioned in the outer tube, a central axis of the inner tube parallel to the outer tube central axis, including third and fourth ends, the third end closer to the first end than the fourth end and open in the outer tube; a partition tube including fifth and sixth ends widening from the fifth end toward the sixth end, the fifth end connected with the fourth end, part of the sixth end connected on an inner surface of the box; and fluid in a space formed by the outer tube and the box.

Abstract: A nuclear device including a plurality of heat pipes; a first fuel configured to surround respective of the plurality of heat pipes coaxially with respect to a central axis of each of the respective heat pipes, the first fuel containing a fissile material at a first enrichment level; a second fuel configured to directly abut the first fuel on the outside of the first fuel and farther than the first fuel from the respective heat pipes surrounded by the first fuel, the second fuel containing the fissile material at a second enrichment level less than the first enrichment level; and a core including the heat pipes arranged in parallel with each other.

Abstract: According to one embodiment, a heat transport apparatus includes an evaporator, a cooling unit, a channel structure, and a heating mechanism. The evaporator vaporizes a refrigerant by heat generated by a heat-generating element. The cooling unit is provided above the evaporator and cools and condenses the refrigerant vaporized in the evaporator. The channel structure constitutes a channel through which the refrigerant circulates between the evaporator and the cooling unit. The heating mechanism heats the cooling unit and suppresses solidification of the refrigerant at the cooling unit.

Abstract: According to one embodiment, a heat transport apparatus includes an evaporator, a cooling unit, a channel structure, and a heating mechanism. The evaporator vaporizes a refrigerant by heat generated by a heat-generating element. The cooling unit is provided above the evaporator and cools and condenses the refrigerant vaporized in the evaporator. The channel structure constitutes a channel through which the refrigerant circulates between the evaporator and the cooling unit. The heating mechanism heats the cooling unit and suppresses solidification of the refrigerant at the cooling unit.

Abstract: A heat pipe, includes; an outer tube including a first end and a second end, the first end closed to be air tight; a box connected to the second end of the outer tube, a cross-sectional area of the box perpendicular to the central axis of the outer tube is larger than a cross-sectional area of the outer tube perpendicular to its axis; an inner tube positioned in the outer tube, a central axis of the inner tube parallel to the central axis of the outer tube, including a third end and a fourth end, the third end of the inner tube closer to the first end of the outer tube than the forth end of the inner tube and open in the outer tube; a partition tube including a fifth end and a sixth end and wider from the fifth end toward the sixth end, the fifth end of the partition tube connected with the fourth end, a part of the sixth end connected on an inner surface of the box; and a fluid in a space formed by the outer tube and the box.

Abstract: A thermal-neutron reactor core includes: a solid moderator expanding to a lengthwise direction; a fuel in the moderator, parallel to the lengthwise direction of the moderator, the fuel containing a fissile material; a cooling tube parallel to the lengthwise direction of the moderator; and a plurality of kinds of burnable poison included in the fuel. The may contain a metal hydride. Furthermore, the plurality of kinds of burnable poison may include one burnable poison containing a concentration of one particular isotope of that one burnable poison.

Abstract: According to an embodiment, a design method for a light-water reactor fuel assembly comprises: accumulating a determined fuel data, showing that each of a combination of p·n/N and e is feasible as the core or not, wherein N is a number of the fuel rods in the fuel assembly, n is a number of the fuel rods containing the burnable poison, p is a ratio wt % of the burnable poison in the fuel, and e is an enrichment wt % of the uranium 235 contained in the fuel assembly; formulating a criterion formula which determines whether a combination of p·n/N and e is feasible as a core or not and is formulated based on the determined fuel data; and determining whether a temporarily set composition of the fuel assembly is approved as a core or not based on the criterion formula.

Abstract: Light water reactor fuel assemblies each comprises: light water reactor fuel rods that extend longitudinally, contain nuclear fuel materials including enriched uranium, and are arranged parallel to each other; and burnable poison containing fuel rods that extend longitudinally, contain nuclear fuel materials whose main component is uranium that is lower in enrichment than the enriched uranium of the light water reactor fuel rods, and burnable poison, and are arranged in a lattice pattern together with the light water reactor fuel rods. The assemblies are arranged parallel to each other and in a lattice pattern. An initial value of a first enrichment of the enriched uranium is set in such a way that the first enrichment of the enriched uranium at an end of each operation cycle is greater than a predetermined value.

Abstract: A nuclear device, including: a heat pipe; a first fuel allocated around a side surface of the heat pipe parallel to a central axis of the heat pipe, the first fuel containing a fissile material at a first concentration; a second fuel allocated on an outer side of the first fuel and containing the fissile material at a second concentration less than the first concentration; and a core including a plurality of the heat pipes arranged in parallel to each of the central axis in the first fuel or in the first fuel and the second fuel.