JPH0545156B

The invention relates to an improved water displacer rod for use in a nuclear fuel assembly. The rod (30) comprises a relatively thin-walled tube (36) sealed at both ends thereof and containing a stack of substantially cylindrical pellets (34) each of which is hollow and defines an inner void (48) individually sealed from the inner voids of adjacent pellets. The pellets with the sealed voids therein increase the collapse-resistance of the thin-walled tube without destroying its lateral flexibility or unduly increasing its mass, and they also prevent reactor coolant from flooding the tube in the event rupture thereof occurs.