Nuclear fuel assemblies

Purpose: To prevent the bending of fuel pins and eliminate the scratching damage resulted to the fuel pins due to mechanical interactions by moderating the tension of wire spacers remarkably developed by the repeating rise and shutdown of the reactor power. Constitution: In a nuclear fuel assembly containing a plurality of fuel pins each spirally wound around at the outer circumference thereof with wire spacers are accommodated in a wrapper tube, a hole is perforated axially to the lower end plug portion formed at the lower end of the fuel pin, a movable member and a biasing mechanism for biasing the movable member are contained in the hole and one end of the wire space is secured to the movable member. Accordingly, bending of the fuel pin caused by the difference in the thermal expansion between the fuel cladding tube and the wire spacer can be overcome. This can eliminate the occurrence of scratching damages to the fuel pins resulted from the mechanical interactions between adjacent pins. (Yoshihara, H.)