Hitachi, Ltd.

Hitachi Engineering Co., Ltd.

Hitachi Nuclear Engineering Co., Ltd.

Hajime Umehara

Masahisa Inagaki

Junjiro Nakajima

Tetsuo Yasuda

Shozo Nakamura

Osamu Yokomizo

Yasunori Bessho

Isao Masaoka

Hideo Maki

Yuichiro Yoshimoto

Iwao Takase

Toshimi Yoshida

Junichi Yamashita

Keiichi Kuniya

Koji Nishida

Satoshi Kanno

Hideki Kurosaki

Yoshihiko Yanagi

Ryutarou Jimbow

Motoo Aoyama

Fuminobu Takahashi

Masahiro Koike

Jiro Kuniya

Katsumasa Haikawa

Tatsuo Hayashi

Hiromasa Hirakawa

Yasuhiro Aizawa

Masayoshi Kanno

Kimihiko Akahori

Yoshihiro Michiguchi

Hideo Soneda

Akira Maru

Hiromichi Imahashi

Yoshiaki Nagashima

Mitsunari Nakamura

Hideaki Ishizaki

Tadashi Mizuno

Toraki Sakuma

Kenichi Fujiwara

Masayoshi Ajima

Kenji Kanamori

Masao Sato

Toshihiro Matsumoto

Norihisa Fujii

Makoto Irube

Nobuo Tada

Ultrasonic waves from a transmit device are transmitted to an object subject to measurement. A surface reflected wave propagated in a contact medium and reflected at the surface of a tube and bottom surface reflected waves passing through an oxidation layer on the tube and reflected at the inner surface of the tube are convened into electric signals. A feature extracting part 5, in consideration of a correlation relationship of energy with respect to the frequency of a received signal, based on the received signal of ultrasonic waves converted to electric signals, extracts a signal feature data determined beforehand which has a strong correlation relationship with the thickness of a measured part. Based on the extracted signal feature data, a thickness conversion part references a relationship storage part which has stored therein beforehand a function that shows a relationship between the signal feature data and the thickness of the oxidation layer, and obtains the thickness of the oxidation layer.

Method and apparatus for measuring thickness of layer using acoustic

The lower end of each of a plurality of fuel rods is supported by a fuel supporting portion of a lower tie plate. The fuel supporting portion includes a plurality of second coolant paths for supplying a coolant from below the fuel supporting portion to a first coolant path defined above the fuel supporting portion and between the fuel rods. The total cross-sectional area of all the second coolant paths is smaller than the cross-sectional area of the first coolant path. A water rod disposed between the fuel rods each includes an ascending tube path having therein a coolant ascending path having a coolant inlet port opening to a region below the fuel supporting portion, for guiding upward the coolant supplied through the coolant inlet port, and a descending tube having therein a coolant descending path having a coolant delivery port opening to said first coolant path, for guiding downward the coolant guided by said coolant ascending path and discharging the coolant through the coolant delivery port to the first coolant path. The descending tube path is so disposed outside the ascending tube path as to define a gap, through which the coolant inside the first coolant path flows, between it and the ascending tube path.

Fuel assembly and nuclear reactor

A mean uranium enrichment of fuel rods is set to not less than 4 wt% and preferably 4.25%, a percentage in number of Gd rods to all the fuel rods is set in the range of 20 to 30% and preferably 23%, and an enrichment 4.45 wt% of the Gd rods is between a pellet maximum uranium enrichment and a pellet minimum uranium enrichment. A percentage in number of those fuel rods having a maximum uranium enrichment of 5.0% to all the fuel rods except the Gd rods is set to not less than 75% and preferably 82%. A mean uranium enrichment in the enriched fuel section except blanket regions at upper and lower end portions is 4.75 wt% and a ratio e.sub.max /e.sub.mean of the pellet maximum uranium enrichment to that mean uranium enrichment is not larger than 1.16 and preferably 1.105. Accordingly, when the maximum uranium enrichment is limited to 5.0 wt%, the mean uranium enrichment can be raised to attain mean discharged exposure not less than 45 GWd/t without causing any problems in gadolinia containing fuel rods.

Nuclear fuel assembly and core

A fuel assembly comprises a plurality of fuel rods supported by an upper tie plate and a lower tie plate respectively at each of upper end portion ad lower end portion, and a channel box surrounding a bundle of the fuel rods and the lower tie plate. The fuel assembly forms a natural uranium region at lower end portion of effective fuel length portion. A wall thickness at a lower thick wall region of the channel box is thicker than the wall thickness at a region disposed upwardly from the lower thick wall region and between corner portions of the channel box. An upper end of the lower thick wall region is disposed from an upper side of the lower tie plate and downwardly from an upper end of the natural uranium region. A wall thickness at the corner portion of the channel box is thicker than the wall thickness at a middle portion of the side wall between the corner positions at the region locating upward from the lower thick wall region. The fuel assembly is able to reduce stresses caused in the channel box during an earthquake, and, is able to improve fuel economy.

Fuel assembly

A fuel assembly comprises a plurality of fuel rods, a lower tie plate for supporting lower ends of the fuel rods, and a channel box surrounding a bundle of the fuel rods and the circumference of the lower tie plate to thereby define a cooling water leak passage between the lower tie plate and the channel box. The fuel assembly includes a venturi provided in the lower tie plate for generating a force tending to attract the channel box toward the lower tie plate under the action of a leak stream of the cooling water passing through the cooling water leak passage. The fuel assembly also includes an arrangement provided in the lower tie plate for suppressing vibrations of the channel box caused upon an influence of the venturi.

Each of cylindrical members composing a fuel spacer of separate cell type is formed at a edge portion thereof with a positioning notch or a positioning projection, which is located just opposite to one of fuel rod supporting projections formed on the inner surface of the cylindrical member. In manufacturing of the fuel spacer, the positioning notches or projections of the cylindrical members are engaged with the positioning projections or recesses formed on fuel spacer assembly jigs for precise and easy positioning of cylindrical members.

Fuel spacer of separate cell type and manufacturing method therefor

A channel box and/or a spacer of a fuel assembly is a welded construction and made of a Zr-Nb-Sn alloy comprising 0.5-2.2 wt % Nb, 0.5-1.5 wt % Sn contained so as to satisfy the relation of Sn(wt %) 22.times.Nb(wt %)--3.0, and balance Zr or a Zr-Nb-Sn-Mo alloy comprising 0.5-2.2 wt % Nb, 0.5-1.5 wt % Sn contained so as to satisfy the relation of Sn(wt %).gtoreq.2.times.Nb(wt %)--0.3, 0.1-0.8 wt % Mo, and balance Zr. The welded portion, its heat affected zone and the unwelded portion of the channel box and/or the spacer have substantially the whole equilibrium phase structure.

Nuclear reactor fuel assembly

A method of producing a composite nuclear fuel cladding lined with a liner of high purity zirconium characterized in that a raw material of zirconium sponge disposed in a hearth cavity is irradiated with an electron beam while controlling an amount of heat per unit volume (w.sec/mm.sup.3) according to an oxygen removal rate of the raw material determined by oxygen concentration of the raw material and a target oxygen concentration of an ingot for a liner to be refined, and zircaloy cladding is lined with the liner. The hearth cavity has a preferable shape in which the ratio of the cavity surface to the cavity volume is 0.20 mm.sup.-1 or larger.

Method of producing composite nuclear fuel cladding

In a process for producing a zirconium-based alloy in which after the zirconium-based alloy is subjected to hot plastic working, it is subjected to cold plastic working and then to annealing and these steps are repeated at least twice, the present invention provides a process for producing a zirconium-based alloy characterized in that after the alloy is subjected to solid solution treatment in which it is heated to a temperature within the range including the .alpha. phase and the .beta. phase of the alloy, or within the range of the .beta. phase and is then quenched, cold plastic working is effected at least twice.

Process for producing zirconium-based alloy

Process for producing zirconium-based alloy and the product thereof

A high-purity metal member is produced by charging raw material such as sponge zirconium into a cavity of a mold such as a hearth under a vacuum atmosphere; irradiating the material with electron beams to melt it at a limited area of the cavity while forming a molten metal pool and irradiating the pool with the electron beam thereby elevate the molten metal pool to evaporate away impurities therein; and shifting the mold relative to the electron beams to provide a high-purity metal member. The metal pool is limited in its size and irradiated high energy density electron beams so that the temperature is raised whereby the impurities are easily evaporated away. The mold may have an annular cavity. In case of high-purity sleeve formation, the electron beams are irradiated onto the raw material while rotating the mold so that melting and solidification appear in a circumferential direction to be repeated. The impurities are repeatedly exposed to the electron beams.

Method of producing high-purity metal member

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Katsuta, Japan

Hajime Umehara