| 摘要 |
PURPOSE:To intend upgrading of a hydrodynamic stability in a fuel channel and also a stability of reactor core, by providing a ring orifice for diminishing a coolant flow cross-section between a lower tie-plate and a fuel support metal fixture. CONSTITUTION:A number of fuel rods 2 are orderly placed in a shape of a grid in a channel box, and its upper end and lower end are supported by an upper tie-plate 3 and a lower tie-plate 4, respectively. And between the lower tie-plate 4 and a fuel support metal fixture 7, a ring orifice 8 for a fuel assembly is inserted. The orifice 8 has a ring 20 and three support plates 21 extending upwardly from an outer edge of the ring. The ring 20 is attached to a position where the ring does not touch with a nose 4a of the lower tie-plate 4 and the support plates 21 are put on the fuel support metal fixture 7 contacting with the lower tie-plate 4. The orifice 8 is freely attachable and detachably by using a jig from an upper position and, thereby, a pressure loss is diminished by removal of the orifice in case that a crud appears at this part. |
