Resistance welding of an end cap for nuclear fuel rods

Abstract

An open end of a cladding tube of a nuclear fuel rod is plugged with an end plug having a main body and a cylindrical bond portion extending from the main body and terminating in a cladding seat with reduced diameter compared with the cylindrical bond portion. The plugging includes clamping the open end of the cladding tube against the cladding seat of the end plug and, while clamping, applying electrical current between the end plug and the open end of the cladding tube so as to force the open end of the cladding tube over the cladding seat and slide over the cylindrical bond portion of the end plug and to generate a resistance weld between a cylindrical bonding surface of the cylindrical bond portion of the end plug and the inside surface of the open end of the cladding tube.

We claim: 
     
         1 . An apparatus comprising:
 a nuclear fuel rod including:
 an end plug having a cylindrical bond portion, a tapered tip at one end of the end plug, and a seat portion of reduced diameter compared with the cylindrical bond portion at the opposite end of the end plug; 
 a cladding tube having an end plugged by the cylindrical bond portion of the end plug with the seat portion disposed inside the plugged end of the cladding tube and the tapered tip extending outside of the plugged end of the cladding tube; and 
 a weld bonding the cylindrical bond portion of the end plug and the inside surface of the plugged end of the cladding tube. 
   
     
     
         2 . The apparatus of  claim 1  wherein the weld is a resistance weld. 
     
     
         3 . The apparatus of  claim 1  wherein the seat portion comprises a cylindrical seat portion of reduced diameter compared with the cylindrical bond portion. 
     
     
         4 . The apparatus of  claim 1  wherein the seat portion comprises a chamfered or frustoconical end of the cylindrical bond portion of the end plug. 
     
     
         5 . The apparatus of  claim 1  wherein the end plug further has a cylindrical main body disposed between the cylindrical bond portion and the tapered tip, the cylindrical main body extending outside of the plugged end of the cladding tube and terminating in the tapered tip. 
     
     
         6 . The apparatus of  claim 5  wherein the cylindrical main body has a larger diameter than the cylindrical bond portion and an abrupt or gradual annular step is defined between the cylindrical main body of the end plug and the cylindrical bond portion of the end plug. 
     
     
         7 . The apparatus of  claim 6  wherein the end plug further has an annular groove in the cylindrical bond portion at the abrupt or gradual annular step defined between the cylindrical main body and the cylindrical bond portion. 
     
     
         8 . The apparatus of  claim 7  wherein the annular groove contains buildup material generated during formation of the weld. 
     
     
         9 . The apparatus of  claim 1  wherein the end plug further includes a stub protruding from the seat portion, the stub not contacting the cladding tube. 
     
     
         10 . The apparatus of  claim 1  wherein the nuclear fuel rod further includes a stack of fuel pellets comprising fissile material disposed in the cladding tube. 
     
     
         11 . The apparatus of  claim 10  further comprising:
 a pressure vessel containing a nuclear reactor core comprising an array of said nuclear fuel rods immersed in primary coolant water. 
 
     
     
         12 . An apparatus comprising:
 an end plug for plugging an end of a nuclear fuel rod cladding tube, the end plug including:
 a tapered tip at one end of the end plug; 
 a cylindrical bond portion sized to form an interference fit inside the end of the nuclear fuel rod cladding tube; and 
 a seat portion of reduced diameter compared with the cylindrical bond portion at the opposite end of the end plug from the tapered tip. 
   
     
     
         13 . The apparatus of  claim 12  wherein the end plug further includes a cylindrical main body of diameter D 1  disposed between the tapered tip and the cylindrical bond portion, and the cylindrical bond portion has diameter D 2  which is less than diameter D 1  of the cylindrical main body. 
     
     
         14 . The apparatus of  claim 13  wherein the seat portion comprises a cylindrical seat portion having diameter D 3  which is less than diameter D 2  of the cylindrical bond portion. 
     
     
         15 . The apparatus of  claim 13  wherein the seat portion comprises a chamfered or frustoconical end of the cylindrical seat portion.