Measurement of Tritium during Voloxidation of Zircaloy-2 Cladding

Abstract

A straightforward method to determine the tritium content of Zircaloy-2 cladding hulls via oxidation of the hulls and capture of the volatilized tritium in liquids has been demonstrated. Hull samples were heated in air inside a thermogravimetric analyzer (TGA). The TGA was rapidly heated to 1000°C to oxidize the hulls and to release absorbed tritium. To capture tritium, the TGA off-gas was bubbled through a series of liquid traps. The concentrations of tritium in bubbler solutions indicated that nearly all of the tritiated water vapor was captured. The average tritium content measured in the hulls was 19% of the amount of tritium produced by the fuel, according to ORIGEN2 isotope generation and depletion calculations. Published experimental data show that there is an initial, nonlinear oxidation rate for Zircaloy-2 followed by a faster, linear rate after “breakaway” of the oxide film and that the linear rate follows an Arrhenius model. This study demonstrates that the linear oxidation rate of Zircaloy samples at 974°C is faster than predicted by the extrapolation of data from lower temperatures.