Hitachi, Ltd.

Hitachi Engineering Co., Ltd.

Kabushiki Kaisha Toshiba

General Electric Company

Takaaki Mochida

Junichi Yamashita

Katsumasa Haikawa

Motoo Aoyama

Junichi Koyama

Akihiro Yamanaka

Akiko Kanda

Osamu Yokomizo

Yoshiyuki Kataoka

Yasuhiro Masuhara

Akihito Orii

Yuichiro Yoshimoto

Kotaro Inoue

Tatsuo Hayashi

Michihiro Ozawa

Shinichi Kashiwai

Akio Tomiyama

Toshiro Yoshioka

Mamoru Nagano

Ryoji Masumi

Hideo Soneda

Mitsunari Nakamura

Tsuyoshi Nakajima

Yoko Ishibashi

Takao Igarashi

Yoko Yuchi

Kenmi Narita

Shigetada Tanabe

Shinichi Kirihara

A resistance member (e.g., fuel holding portion of the lower tie plate) is provided at the lower end of the fuel assembly. Provision is made of a coolant ascending path in which said water rods have coolant inlet ports that are open in a region lower than the resistance member to upwardly guide the coolant, and a coolant descending path which has a coolant delivery port that is open in a region higher than the resistance member to downwardly guide the coolant. The coolant ascending path and the coolant descending path are communicated with each other at their upper end portions.

Fuel assembly and nuclear reactor

Method of operating reactor

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 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. Thereby, it is possible to greatly decrease the number of pieces of the replacement fuel.

Fuel loading method

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. According to this arrangement, a greater burn-up degree of the fuel assembly can be achieved with minimal increment of the average enrichment, while preserving sufficiently large safety margin such as the thermal margin of the reactor and the reactor cold shut down margin.

Nuclear fuel assembly and nuclear reactor incorporating the same

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 fuel assembly for a light water reactor comprising a plurality of fuel rods which contain plutonium as a primary fissile material when exposure is zero, and a light water reactor including such fuel assemblies. The fuel assembly has a structure in which at least one of moderator rods is provided at least in one of each corner portion of an arrangement of the fuel rods and a position adjacent to the corner portion in such a manner that the moderator rods are located in rotation symmetry, each of the moderator rods being filled with water or a solid coolant over a length at least corresponding to a fuel effective length, and the fuel rods are provided at positions in the second layer from the outermost periphery which are adjacent to those positions at which the moderator rods are located.

Fuel assembly for light water reactor and light water reactor core

A fuel assembly including a channel box, upper and lower tie plates, fuel rods inserted in the channel box and held at upper and lower end portions by the upper and lower tie plates, a water rod disposed among the fuel rods and spacers for keeping the fuel rods and the water rod spaced from one another. The water rod has a diameter larger than that of each of the fuel rods and the upper end of the water rod has a height substantially as high as an upper end of an effective enriched fuel section of each fuel rod.

Fuel assembly

A nuclear fuel assembly has a plurality of fuel rods each containing a multiplicity of fuel pellets. The fuel rods include a plurality of first fuel rods and a plurality of second fuel rods. Each of the first fuel rods contains a burnable poison over substantially the entire axial length thereof. The first fuel rod also has a greater means enrichment in the upper axial region thereof than that in the lower axial region thereof. Each of the second fuel rods contains no burnable poison and has a uniform enrichment distribution over substantially the entire axial length thereof. In each cross-section of the fuel assembly perpendicular to the axis thereof, the outer peripheral portion has a greater mean enrichment than the central portion. The first fuel rods are disposed in the peripheral portion except the outermost peripheral portion of the cross-section of the fuel assembly.

Nuclear fuel assembly

A fuel assembly for loading in the core of a boiling water reactor comprises a large number of vertically extending fuel rods, some of which contains a burnable poison, where a rod-average uranium enrichment of fuel is higher in the upper region of the fuel assembly than in the lower region and a total content of the burnable poison is lower in the lower region of the fuel assembly than in the upper region and a spectral shift effect of the boiling water reactor is increased while thoroughly maintaining a reactor shutdown margin, and a discharge exposure is increased.

Fuel assembly for boiling water reactor

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Hitachi, Japan

Takaaki Mochida