A desorption model for the code SOLIDUSS and its experimental benchmarking

The code SOLIDUSS is a Monte Carlo based solid-state diffusion software for radiation protection. It was developed to accurately estimate the amount of radionuclides that could escape activated material affected by an accidental fire. A desorption model based on the computation of the desorption probability of those radionuclides reaching the surface of an object was introduced to upgrade the software, proven to be a significant improvement with respect to earlier stages of the code. A set of experiments was performed at CERN to estimate the out-diffusion of radionuclides from activated materials typically used in accelerator environments when exposed to high temperatures. In particular, a 49.3 μm thick Cu foil containing $^{60}$Co and a 94 μm thick Al foil with $^{22}$Na were exposed to approximately 1000 °C and 600 °C respectively for different time periods. Out-diffusion fractions of 1.5 ± 5.5% for $^{60}$Co after 5 h and 22.5 ± 3.1% for $^{22}$Na after 4 h were obtained. A set of SOLIDUSS simulations was carried out replicating the experimental setup and using literature diffusion and desorption activation parameters. The results obtained are in good agreement with the experimental data within error bars. A high sensitivity of the simulation results to changes in the input parameters was observed.