Nuclear fuel assembly

Purpose: To easily and surely prevent unstable vibrations in fuel rods due to jet streams of coolants. Constitution: Fuel cans for a portion of fuel rods situated at or near the outer circumference of a fuel assembly set up by using supporting lattices are made of tubular materials having proper vibrations and vibration damping coefficients equal to or greater than those of zircalloy tubes and having abrasion-resistivity. Fuel cans for the remaining fuel rods in the fuel assembly are made of zircalloy tubes. In this way, the limiting flow rate can be increased and the resistivity of the fuel rod to the jet stream is increased to reduce the unstable vibrations as compared with the nuclear fuel assembly composed only of zircalloy fuel cans. Consequently, abrasion and injury to the fuel cans at the points in contact with the supporting lattices due to the horizontal vibrations of the fuel rods can surely be prevented. (Moriyama, K.)