Development of a Fuel Thermal Diffusivity Measurement Technique Using Pulsed Electron Beams

Abstract

A new technique is being developed for measuring the thermal diffusivity of materials using a 11.4 MeV electron beam. A short, high-current pulse (~0.1 second) of high-energy electrons penetrates axially into one end of a cylindrical sample whose length is a few times the electron range. Thermocouples or remote heat-sensing devices measure the resultant time-dependent temperature distribution on the other end of the sample. A comparison with both reference standards and theoretical predictions allows one to determine the thermal diffusivity. The errors are the result of uncertainties in ( 1) the pulse timing (which is small), (2) the electron penetration distribution, and (3) the rate of heat-loss to the surroundings. Initial proof-of-principle measurements on a fresh U02 CANDU reactor fuel pellet demonstrated accuracy and reproduciblity with a statistical error of < +/- 6%. An added benefit of the technique is that it simultaneously measures the fractional change in the specific heat with temperature.