Abstract
A long-term disposal of a nuclear waste package requires a matrix material that possesses a high thermal conductivity in order to release the decay heat from the fission products. In this study, the thermal diffusivity (a) of alumina borosilicate glass (ABG), encapsulating surrogated tristructural-isotropic (TRISO) particles, has been measured experimentally using the laser flash analysis (LFA) methodology. Image-based models were developed using X-ray computed tomography for glass samples bearing different proportions of TRISO particles. Simpleware software generated finite element (FE) models which then were solved using Abaqus software. The matrices were examined at different waste loadings (10, 20 and 30 wt%) at a temperature of 50 C. The modelling results were in close agreement with the experimental results and the deviations were within the bounds of standard numerical error (\5 %). The thermal diffusivity of the samples was increased with increasing proportion of TRISO particles. For the maximum mechanically stable matrix, the thermal diffusivity was found to be 0.92 ± 0.021 9 10-6 and 0.94 9 10-6 m2 s-1 measured by LFA and modelling,respectively.
Introduction
The thermal diffusivity of alumina borosilicate glass (ABG) bearing TRISO particles plays an important role in estimation of dissipation of radioactive waste heat. The particles were chosen to have SiC outer layer in order to provide chemical compatibility with ABG [1]. SiC layer has the highest thermal conductivity (168 W m-1 K-1) in TRISO particles [2]. This reduces the probability of forming a hot spot in the waste form. As the glass matrix was only recently developed, there were no investigations and/or calculations done for the thermal diffusivity of a glass bearing TRISO particles. However, many studies were directed towards measuring the thermal diffusivity and conductivity of glass and TRISO particles independently. In a previous study, the thermal conductivities of TRISO layers were measured using time-domain thermoreflectance and they are listed in Table 1 [2]. The waste loading (proportion of TRISO particles in the matrix) may play an important role in the heat conduction. Therefore, in this study, the tests were conducted on three specimens bearing different proportions of TRISO particles.
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