Characterization of debris bed generated by fuel coolant interactions

The objective of the present paper is to compare the performance of statistical distributions which are used to describe the size distributions of fragments obtained from molten fuel coolant interactions (MFCI) experiments. Four distributions namely: Weibull, log-normal and upper limit log-normal distributions are employed along with the distribution resulted from the sequential fragmentation theory (SFT) of Brown. The distributions are fitted to two sets of experimental data obtained from jet fragmentation experiments under FCI conditions. One set from JRC/Ispra, KROTOS experimental program and the other set from RIT/NPS, MIRA-20L experimental program, are employed. It is found, among the distributions examined, that the SFT model, using mass mean diameter σ and a free parameter γ, which represent the fractal dimension of the debris, describe the measured data better than the other distributions. The fractal dimension is found to vary between two and three, depending on the size of the fragments (σ). In the case of corium debris the fractal dimension approaches three as the mass mean diameter decreases. For three different oxide melts, the fractal dimension varies between approximately two and three. Additionally, the paper discusses the physical background and the distribution parameters of the SFT. (orig.)