| 摘要 |
PURPOSE:To reduce the pressure drop of a coolant so as to improve power generation efficiency and to increase the allowance of a thermal limit value to fuel by chipping the inside surfaces of a channel box to the thickness smaller nearer the down stream side, thereby widening a flow passage area. CONSTITUTION:A large-sized square cylindrical water rod 3 corresponding to 9 pieces of fuel rods 4 is disposed to the central part in the channel box 1 having a uniform outside shape. The fuel rods 4 are disposed in correct order in 9 lines and 9 rows in the other space part of the channel box 1. The water rod 3 is formed to a thin wall 3b by chipping the wall thickness 3a thereof in such a manner that the sectional area of the flow passage on the down stream side of the cooling water is widened on the outside thereof. The inside surfaces of the channel box 1 are reduced in thickness to 1a, 1b, 1c toward the down stream to widen the inside area. The bundles are not horizontally retained except in the lower part by the mere reduction in the thickness and are, therefore, unstable. Spacer contact parts 2 are locally mounted to the inside surfaces of the channel box 1 and the horizontal positions of the bundles are fixed at these thin-walled parts in order to avoid the above-mentioned instability. |
