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^oC. 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^oC 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^oC was further explored and it was found that vapourization was the dominant pathway. (author)