Temperature distributions in end closures of annular fuel elements

The temperature distributions in bonded end closures of annular fuel elements, such as those often used in nuclear superheating power reactors, are determined analytically. The solution for the temperature distributions is represented by products of the Bessel functions with hyperbolic functions. An illustrative example is that for enriched uranium oxide and plutonium oxide (UO₂.PuO₂) fuel with zircaloy-4 cladding and end closures in an inner (or central) superheating fast-reactor core. The assumed lengths of the end closure are 0.1, 0.5, 1.0 and 1.5 times the outer radius of the fuel element. The calculated results of the example indicate that

• 1.

  1. the temperature distributions in the end closures approach constants as the lengths of the end closures increase;

• 2.

  2. there is an optimum length of end closure for each fuel element design; further increase in its length will waste the end-closure material;

• 3.

  3. the temperature distribution in the thin end closures is approximately linear.

• 4.

  4. to maintain the integrity of fuel elements, surface temperatures of cladding and end closures of the fuel elements must be kept appreciably below the known corrosion temperature limit of the coolant.