Reconstitutable control assembly having removable control rods with detachable split upper end plugs

In a reconstitutable control assembly for use with a nuclear fuel assembly, said control assembly including a spider structure and at least one control rod, an attachment joint for detachably fastening said control rod to said spider structure, said attachment joint comprising:

• (a) a hollow connecting finger on said spider structure;
• (b) an elongated detachable split upper end plug on said control rod having a pair of separate upper and lower plug portions, said upper plug portion having integrally-connected tandemly-arranged upper, middle and lower sections, said lower plug portion having integrally-connected tandemly-arranged upper, middle and lower segments;
• and
• (c) a radially flexible and expandable thread-defining means;
• (d) said upper section of said upper plug portion being rigidly attached to said connecting finger on said spider structure, said lower segment of said lower plug portion being rigidly connected to said control rod;
• (e) said lower section of said upper plug portion and said middle segment of said lower plug portion being complementarily threaded to receive therebetween said radially flexible and expandable thread-defining means for threaded engagement therewith in a relationship in which said thread-defining means frictionally resists rotation of said upper and lower plug portions relative to one another;
• (f) said middle section of said upper plug portion and said upper segment of said lower plug portion being complementarily configured for defining a slip fit joint between said upper and lower plug portions.