Determination of the activation energy of tritium diffusion in ceramic breeders by reactor power variation

Abstract

In this work, the analysis of experimental results on the irradiation of lithium ceramics Li2TiO3 is presented. Lithium ceramics samples were irradiated at the WWR-K research reactor (Almaty, Kazakhstan) under continuous pumping conditions at a temperature of ~610°C for ~21 days with a thermal neutron flux of ~5•1013 n/(cm2•s). During the experiment, the release of tritium-containing molecules (HT, T2, HTO and T2O) was recorded by a mass-spectrometric method. During the reactor experiment with a frequency of about one to two times a day, a short-term (less than 10 minutes) reduction of reactor power by 25-50 % was conducted, with subsequent regain. In this case, as expected, samples temperature and the released flows of tritium-containing molecules decreased. This mode of reactor operation and obtained data allowed us to propose a method for assessing the temperature dependence of the diffusion coefficient of tritium in ceramics under reactor irradiation. This method assumes that with a rapid change in the reactor power and the sample temperature, the tritium concentration in the surface region does not change much. In contrast, the diffusion coefficient (which has an Arrhenius temperature dependence) varies greatly. It determines the decrease in tritium flows from the sample. In the paper, several sections of reactor power decrease/increase are analyzed, which are used to evaluate the diffusion coefficients of tritium in ceramics under reactor irradiation.