System providing improved guidance support with restricted coolant flow for control rods in the upper head plenum of a nuclear reactor.

摘要

A new system is provided for control rod guidance support with wear mitigating features in a nuclear reactor pressure vessel. A plurality of externally driven control rod assemblies each have a drive rod coupled to a depending control rod and upper and lower guide tubs extend vertically through upper head plenum and outlet plenum coolant spaces above the reactor core. The upper guide tube and the lower guide tube have a plurality of horizontal support cards secured therein at vertically spaced locations and having openings therethrough to provide guided support for multiple depending rodlets of the control rod when it is positioned and as it moves along its vertical path of motion. The upper guide tube has a top enclosure plate with a drive rod opening therethrough sized to provide a predetermined clearance space between the drive rod and the top enclosure plate and to direct coolant flow between the upper and outlet plenums and through the guide tube assembly to allow transmittal of upper plenums bypass cooling flow to the outlet plenum. Stucture is provided for restricting coolant flow through the top plate clearance space to reduce control rod wear.