Spacer for fuel assembly

Since a limit power of a fuel assembly greatly depends upon the shape of a spacer, a spacer plate is made thinner in the lower side compared with that in the upper side. In a ring element type, the thickness of the ring element is reduced in the lower side of the spacer than that in the upper side. Alternatively, the space or the ring element is tapered so that the thickness thereof is reduced in the lower side than that in the upper side. In each of the cases, since the cross sectional area of the flow channel at the lower portion of the spacer is increased than that in the upper portion, the resistance is reduced and coolants flow more easily. Vortex flows are less caused at the lower end face of the spacer, to prevent burnout and improve the limit power. (N.H.)