PURPOSE: To prevent fuel rods from being damaged by foreign matters caught by the lowest grid by providing a fretting preventing protective device which has a grid attaching structure extended over the lower end section of a fuel rod sheath and composed of hollow sleeves arranged around the lower end section.
CONSTITUTION: A hollow sleeve 40 is constituted to prevent the fretting of the lower end section 23A of a fuel rod sheath 23. The sleeve 40 is separated from the lower end section 23A of the sheath 23 and attached to a grid 16A in such a way that the sleeve 40 is fitted to the side wall 50 of a grid cell 40 by brazing, welding, etc. The sleeve 40, in addition, is extended to cover the entire peripheral surface of the lower end section 23A so that the sleeve 40 can prevent foreign matters carried by an upward coolant flow from coming into contact with the lower end section 23A and, accordingly, the fretting of the lower end section 23A.
UOOREN REEN MOOTARAA
HARII MATSUKUSU FUERAARI
ROBAATO NIKORASU SUTANUTSUTSU
