Leak control device for coolant in fuel assembly

Purpose: To always keep the amount of coolants constant leaking through the gap between a channel box and a lower tie plate irrespective of creep deformation during irradiation. Constitution: A gap is provided between the lower portion of a channel box and the side of a lower tie plate for leaking a predetermined amount of coolants. A recess is formed in the side of the tie plate, within which is loosely fitted a leak control element having an expanded portion generally conforming the outer side surface of the tie plate and having at its upper portion an opening for the inlet of the coolants. The control element is thus urged to the lower inner surface of the channel box by way of the coolant pressure from above the lower tie plate to make the coolant leak constant. (Furukawa, Y.)