| 摘要 |
PURPOSE:To prevent the damage of a covering tube contacting with pellets, by forming longitudinal grooves on the outer circumferential surfaces of fuel pellets, and by shaping portions among adjacent grooves in curved surface forms by expanding said portions in petal-like shapes. CONSTITUTION:A number of longitudinal grooves 14 with gentle inclinations are formed on the outer circumferential surfaces of fuel pellets 12, and portions among adjacent grooves 14 are expanded in petal-like shapes and changed into curved surfaces 15. Ridgeline portions among the upper and lower end surfaces of the pellets 12 and the curved surfaces 15 are formed in beveling shapes 16. The thermal expansion and swelling of the pellets 12 are absorbed by forming longitudinal through holes 18 to the central portions of the pellets 12 at locations that are parallel to the central axes and are eccentric. The directions of the pellets 12 are shifted so that the longitudinal through holes 18 not be continued, and the pellets are inserted into a covering tube 11, thus preventing the local lowering of heat transfer. When a reactor is being operated, the concentration of distortion decreases because contact surfaces among the pellets 12 and the covering tube 12 are smooth, and the damage of the covering tube 12 can be prevented.
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