Radon transport in porous materials; application to the restoration of a phosphogypsum repository

The pilling of waste materials with high ²²⁶Ra concentrations like phosphogypsum represents a potential health risk in many countries, making it important to understand radon transport through soils and develop mitigation techniques. The objective of this work is to develop and validate an open-source algorithm for evaluating radon transport through porous materials, and its application to estimate the radon exhalation depending on the applied restoration. Methodology has been validated by comparing our algorithm with literature data. A mean relative difference of 10% between our algorithm and the literature experimental measurements, and 14% with the literature model results were found. A sensitivity analysis was done by varying the input parameters and different boundary conditions were tested. The algorithm was compared against laboratory simulations of a phosphogypsum repository in Spain, with a mean relative difference of 13% compared with our results. Among the radon mitigation covers tested, the lowest exhalation was achieved by a geomembrane sheet. It was also tested with in-situ measurements of already restored sections of the repository finding a mean relative difference of 6% between the measurements and the algorithm. The measured topsoil cover reduction was 18%, and the algorithm estimated a 17% reduction in radon exhalation. In conclusion, an open-source alternative to the exhalation prediction of multi-layer soils was created, validated and gave accurate estimations.