Nuclear fuel rod having cladding with varying diameter

A variable diameter fuel rod of a nuclear reactor assembly, the variable diameter fuel rod comprising:

• a sealed elongate cladding tube, comprising:
• a top end;
• a bottom end;
• an axial reflector region adjacent the top end;
• and
• an axial region positioned below the axial reflector region;
• a plurality of solid fuel pellets positioned in the axial region;
• a plurality of annular fuel pellets positioned in the axial reflector region, wherein an outside diameter of each of the plurality of solid fuel pellets and an outside diameter of each of the plurality of annular fuel pellets is the same, wherein neutrons are reflected by the plurality of annular fuel pellets to the axial region, and wherein the plurality of annular fuel pellets comprise:
• a first annular fuel pellet adjacent the top end of the sealed elongate cladding tube;
• and
• a second annular fuel pellet positioned below the first annular fuel pellet;
• a first annular gap defined between the outside diameter of the first annular fuel pellet and a first inner cladding diameter defined by the sealed elongate cladding tube in the axial reflector region;
• and
• a second annular gap defined between the outside diameter of the second annular fuel pellet and a second inner cladding diameter defined by the sealed elongate cladding tube in the axial reflector region, wherein the first annular gap is larger than the second annular gap.

A variable diameter fuel rod of a nuclear reactor assembly, the variable diameter fuel rod comprising:

• a sealed elongate cladding tube, comprising:
• a top end;
• a bottom end;
• an axial reflector region adjacent the top end;
• and
• an axial region positioned below the axial reflector region;
• a first plurality of fuel pellets positioned in the axial region;
• a second plurality of fuel pellets positioned in the axial reflector region, wherein neutrons are reflected by the second plurality of fuel pellets to the axial region, wherein the second plurality of fuel pellets are stacked on top of each other in a fuel pellet stack extending along the entire axial length of the axial reflector region, and wherein the fuel pellet stack defines an outside diameter;
• a first annular gap defined between the outside diameter of the fuel pellet stack and a first inner cladding diameter defined by the sealed elongate cladding tube in the axial reflector region;
• and
• a second annular gap defined between the fuel pellet stack and a second inner cladding diameter defined by the sealed elongate cladding tube in the axial reflector region, wherein the first annular gap is larger than the second annular gap, and wherein the first annular gap is positioned above the second annular gap.