Distribution of radionuclides between atmosphere and ash during combustion of contaminated vegetation

A series of laboratory-scale combustion tests were conducted under well-controlled conditions to measure the release of 90Sr and 137Cs nuclides to the atmosphere (air) from combustion of vegetation and organic soil samples contaminated with radioactivity. These vegetation and soil samples were collected from a controlled contaminated forest area within the Canadian Nuclear Laboratories - Chalk River site. The combustion products including ash and smoke particulates, along with gaseous emissions, were collected and then analyzed for 137Cs and 90Sr concentrations by radiometric techniques. The experimental results reveal that the releases of 90Sr to the atmosphere (air) from combustion of vegetation are very low with most of the 90Sr activity remaining in ash residues, even at a temperature of 800 °C. The detailed combustion experiments with surface litter and twigs, alder twigs, alder leaves, and organic soil indicate that 0.5 ± 0.1%, 0.3 ± 0.1%, 0.9 ± 0.1%, and 0.3 ± 0.1% of 90Sr is released to the atmosphere (air), respectively. On the other hand, the releases of 137Cs are found to be highly dependent on the combustion temperature as well as the nature of vegetation. The releases of 137Cs obtained at 800 °C are 45 ± 7%, 77 ± 9%, 92 ± 5%, and 2.4 ± 0.5% for surface litter and twigs, alder twigs, alder leaves, and organic soil, respectively. The mechanism associated with the high release of 137Cs at a high temperature of 800 °C was explored.