Hitachi, Ltd.

Hitachi Engineering Co., Ltd.

Yoshishige Kawada

Hiromasa Hirakawa

Shozo Nakamura

Osamu Yokomizo

Junjiro Nakajima

Yasuhiro Masuhara

Yasuhiro Aizawa

Toshitsugu Nakao

Tetsuo Yasuda

Shin-ichi Kashiwai

Akira Maru

Akio Tomiyama

Shigeto Murata

Yorihide Segawa

Yoshihiko Yanagi

Tadashi Mizuno

A nuclear fuel assembly has a plurality of fuel rods and a lower tie plate supporting their lower ends. Coolant apertures extending through the lower tie plate. A channel box surrounds the fuel rods and receives the lower tie plate, to confine the coolant. To restrict leakage of coolant between the tie plate and the channel box, the coolant apertures include, adjacent the periphery of the lower tie plate, a plurality of peripheral apertures which are located at least partly outside the outermost fuel rods. The peripheral apertures each provide a coolant velocity peak located further from the axial center line of the tie plate than the axial center lines of the closest neighboring fuel rods. The invention also provides venturis in the leakage path between the channel box and the tie plate, to restrict deformation of the tie plate.

Nuclear fuel assemblies

A fuel assembly according to the present invention is formed in such a manner that the small diameter portion of an upper end plug of a fuel rod is inserted into a boss of an upper tie-plate. The upper end plug includes a small diameter portion and a large diameter portion which is disposed below the former. An expansion spring in disposed in the small diameter portion of the upper end plug. A cover member surrounding this expansion spring is disposed in the large diameter portion of the upper end plug, and extends upwardly. Since the cover member surrounds the expansion spring, pressure loss caused by the expansion spring can be reduced.

Fuel assembly

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Hitachi, Japan

Yoshishige Kawada