Transient temperature distributions in end caps of plate fuel elements

The transient temperature distribution in bonded end caps of plate-type fuel elements submitted to sudden temperature change resulting from unsteady-state reactor operation is analytically determined. The solution for the temperature distribution is represented by products of circular function, exponential functions and coupling relations between the end caps and the fuel material of the fuel elements. From the calculated results of a numerical example given for a ceramic dispersion fuel element with zircaloy end caps, the following points of primary interest are found:

• 1.

  (a) For a given end-cap material, the temperature distribution for end caps of various depths (or thicknesses) is the same, if the time of heat conducting is proportional to the square of the depth.

• 2.

  (b) The temperature distribution in the end cap decreases with increasing end-cap length and Fourier number.

• 3.

  (c) Repeated sudden temperature changes that induce severe thermal shock, cycling, fatigue, and temperature excess can seriously affect the corrosion rates and impair the structural integrity of the end caps as well as the fuel elements. Further, the corrosion temperature limit and thermal fatigue of the end cap (or cap of a fuel can) can be much more serious than that of the fuel material.