Control rod guide assembly with enhanced stiffness, fuel assembly including the same, and method of installing control rod guide assembly

A nuclear fuel assembly comprising:

• a top nozzle;
• a bottom nozzle;
• a plurality of grids arranged in between the top nozzle and the bottom nozzle and supporting the guide tubes in the spaced parallel array at spaced axial elevations between the top nozzle and bottom nozzle, the plurality of grids including a bottom grid disposed closest to the bottom nozzle among the plurality of grids;
• and
• a plurality of control rod guide assemblies, at least one of the control rod guide assemblies including:
• a guide tube having an axial dimension, the guide tube being supported by the plurality of grids and extending axially between the top nozzle and the bottom nozzle, the guide tube having an upper portion having a first radius and a lower portion having a second radius less than the first radius;
• and
• an external dashpot tube disposed around a portion of the lower portion in an area beginning at the bottom grid and extending toward the top nozzle.