Hitachi, Ltd.

Other

Junichi Koyama

Motoo Aoyama

Junichi Yamashita

Katsumasa Haikawa

Koji Nishida

Akihiro Yamanaka

Akinobu Nakajima

Yasunori Bessho

Hiromi Maruyama

Takaaki Mochida

Mitsunari Nakamura

Akiko Kanda

Sadao Uchikawa

Masao Chaki

Ryoji Masumi

Michihiro Ozawa

Yoko Ishibashi

Kenmi Narita

Osamu Yokomizo

Akihito Orii

Hiromasa Hirakawa

Tatsuo Hayashi

Yasuhiro Aizawa

Hideo Soneda

Toru Kanazawa

Toshiro Yoshioka

Yoko Yuchi

Yoshihiri Iwashita

Hiroko Haraguchi

Fuel assembly

A fuel assembly includes a plurality of fuel rods placed in a square lattice array of 9-rows/9-columns and at least one water rod. In this fuel assembly, the fuel rod pitch of the plurality of fuel rods is in a range of 14.15 mm to 14.65 mm, and means for offsetting and holding a fuel bundle composed of the fuel rods and the water rod is provided in such a manner that the center in a cross section of the fuel bundle is offset from the center in a cross section of the lower tie plate toward the channel fastener side. With this configuration, it is possible to provide a fuel assembly for a D-lattice core, which is capable of achieving the fuel economy comparable to that of a C-lattice core without reducing the thermal margin, and of using the existing fuel spacers.

Fuel assembly and reactor core and fuel spacer and channel box

Method of operating reactor

Each of short-length fuel rods is arranged at a position other than in 3&times;3 corner regions to in such a manner as not to be simultaneously adjacent to a water rod and others of the short-sized fuel rods. Gd fuel rods are arranged at positions excluding the outer periphery, and the number of those of the Gd fuel rods adjacent to the short-length fuel rods is one-half or less the total number of the Gd fuel rods. At a transverse cross-section of a region upward from upper ends of the short-sized fuel rods , the amount of burnable poison contained in a polygonal region whose vertexes are located at centers of those of the first fuel rods arranged at the outermost layer is smaller than the amount of burnable poison outside the region . With this configuration, a critical power can be improved in consideration of both a distribution of the flow of coolant and a distribution of a thermal power in the fuel assembly.

Initial loading core

Each of short-length fuel rods 3 is arranged at a position other than in 3.times.3 corner regions 6 to 9 in such a manner as not to be simultaneously adjacent to a water rod 5 and others of the short-sized fuel rods. Gd fuel rods 4 are arranged at positions excluding the outer periphery, and the number of those of the Gd fuel rods 4 adjacent to the short-length fuel rods 3 is one-half or less the total number of the Gd fuel rods. At a transverse cross-section of a region upward from upper ends of the short-sized fuel rods 3, the amount of burnable poison contained in a polygonal region 10 whose vertexes are located at centers of those of the first fuel rods 3 arranged at the outermost layer is smaller than the amount of burnable poison outside the region 10. With this configuration, a critical power can be improved in consideration of both a distribution of the flow of coolant and a distribution of a thermal power in the fuel assembly.

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 %.

Initial core

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.

Initial core of nuclear power plant

The reactor shut-down margin and the thermal margin, as well as the output per unit volume of the core is increased. When A is the total cross sectional area of the non-boiling water areas in the channel boxes each surrounding a fuel assembly and non-boiling water areas outside the channel boxes and B is the cross sectional areas of boiling water areas in the channel boxes, the relation of 1&gt;B/(A+B).gtoreq.0.76 is set. A control unit adjusts a rotational speed of a recirculation internal pump which controls the cooling water flow rate per unit area in the core section to 3.0.times.10.sup.3 t/h/m.sup.2 at the beginning of the operation cycle and controls the cooling water flow rate per the unit area in the core cross section to 3.3.times.10.sup.3 t/h/m.sup.2 at the end of an operation cycle.

Boiling water type thermal neutron reactor and its operating method

A fuel assembly and a reactor core using same which are able to increase size of the fuel assembly with ensuring thermal margin and reactor shut down margin. A distance between centers of adjacent fuel assemblies is about 23 cm, which is enlarged about 1.5 times of conventional fuel assemblies. A thickness of water gap region is about 16 cm, which is relatively thinner than that of prior art. While, H/U ratio is about 5 as same as that of the prior art, and decreasing amount of non-boiling water in the water gap region is arranged in a channel box as water rods. Consequently, a ratio of transversal cross section area of the water rods to transversal cross section area of the fuel rods becomes about 0.6, and local power peaking factor can be decreased and thermal margin can be increased. Further, the transversal cross section area of the water rod is selected to be 15 cm.sup.2 so as to ensure the reactor shut down margin by reducing excess reactivity.

Fuel assembly and reactor core

A nuclear fuel assembly has an array of fuel rods comprising a plurality of first fuel rods each containing nuclear fuel material but not containing burnable poison and a plurality of further fuel rods each containing both nuclear fuel material and burnable poison. The further fuel rods comprise second fuel rods and third fuel rods, and each second fuel rod has at a lower region of the fuel assembly a burnable poison concentration which is a minimum burnable poison concentration in the further fuel rods. To increase the effectiveness of the second fuel rods in controlling axial power peaking, as seen in plan view on the array, the first fuel rods are the nearest neighbors of each further fuel rod.

Nuclear fuel assemblies and reactor cores including them

A nuclear fuel assembly for a nuclear reactor has a plurality of vertically extending fuel rods arranged side by side in a square array and containing fissile material. The array has two adjacent first sides which are next to a control rod region of the core and two adjacent second sides which are next to a non-control rod region of the core. When the rods of the array as seen in horizontal cross section, excluding the rods lying on the diagonal line joining the opposite corners of the array at which the control rod region meets the non-control rod region, is divided into four regions which are

Nuclear fuel assembly and nuclear reactor core containing said assembly

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.

Core loading strategy

A fuel assembly has a plurality of first fuel rods each of which contains nuclear fuel material but does not contain burnable poison, and a plurality of second fuel rods each of which includes nuclear fuel material and burnable poison. The amount of burnable poison in a lower region of the fuel assembly is smaller than that in an upper region thereof. When each of the second fuel rods is divided into an upper region and a lower region, a region of the divided regions in the second fuel rods containing a maximum burnable poison concentration Gmax and a region of the divided regions in the second fuel rods containing a minimum burnable poison concentration Gmin are located in the lower region of the fuel assembly. The burnable poison concentration of the upper region of each second fuel rod is between Gmax and Gmin. The fuel assembly may moderate a maximum linear heat rating with an increased spectral shift effect.

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&lt;c/d is satisfied. The reactor core provides sufficient thermal margin and improved cold shutdown margin.

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Hitachi, Japan

Junichi Koyama