To deflect a relatively large quantity of liquid component of a gas- water mixture toward the outside fuel rod while reducing the resistance for the entire flow of coolant passing through a channel.

The spacer comprises a matrix of ferrules F' surrounding individual fuel rods 12' in a fuel band, a band having upper edge 42 surrounding the matrix while defining the circumferential wall of the spacer, and a plurality of flow tabs 44 extending upward from the upper edge 42 while being spaced apart in the lateral direction. Each flow tab 44 has a substantially vertical lower part and an inclining upper part extending from the vertical lower part. The vertical lower part and the inclining upper part are provided a central crease 50' and the flow tab 44 is provided, at the upper and lower parts thereof, with opposite bent parts.