Transition piece for reducing coolant pressure drop for bottom entry nuclear fuel assemblies.

摘要

A nuclear fuel assembly includes a fuel assembly support plate with a round orifice for the passage of a flow stream and having a rectangular or square channel entry area immediately below the fuel assembly. The assembly includes a transition piece for coupling the flow stream from the orifice to the channel entry area. The transition piece has a first cylindrical portion with a constant diameter at least as large as the diameter of the orifice and disposed immediately above the orifice for allowing the flow stream from the orifice to fully enter the first portion and attach to the inner sides of the first portion. A second portion is included for coupling to the channel entry area. The second portion has a rectangular or square upper section and a round lower section. A conical third portion is included for connecting the first portion with the round lower section of the second portion for allowing controlled expansion of fluid in said transition piece. The conical portion has a cross-sectional diameter which increases in the flow direction from the first portion to the second portion for allowing controlled expansion of fluid in the transition piece.