Thermal decomposition of radio-oxidized polymers and impact on radioactive material transportations

Abstract

International audienceIntroductionIn case of accidental conditions of transportation, the temperature of packages can reach 150°C. Theaccumulation of the gases formed may affect the integrity of the package. Therefore, it is important topredict the gas quantity released by different organic materials and measure the kinetic of thisdecomposition. The purpose of this work is to present the results of a multi-year study performed on fourpolymers (polyethylene, cellulose, polyurethane, polyvinyl chloride). The effect of dose, atmosphere anddegradation temperature on the quantity of gas release was investigated.ExperimentalThe polymers were gamma-irradiated under air atmosphere at room temperature at different doses (from 0to 4 MGy). After irradiation, the thermal degradation of polymers at different temperatures (from 60°C to150°C) during 48 hours under two types of atmosphere (air or inert) was analyzed. For that purpose, aknown amount of polymer was conditioned in a small hermetic chamber (made on stainless steel or glass)equipped with a pressure gauge. The pressure elevation during the thermal treatment was recorded. Anidentification and a quantification of the gas phase were also realized using high resolution massspectrometry.Results and discussionIn contrast to the non-irradiated polymers, which are mostly stable even at 150°C, a rapid increase of thepressure during the first hours after heating and a stabilization or a slow increase after is observed for radiooxidized materials. The production of volatile species is almost proportional to the dose and is thermallyactivated. The main degradation products are water and carbon dioxide. The production of hydrogen andinflammable gases is rather limited. Under air atmosphere, the pressure increase is partially compensatedby oxygen consumption.ConclusionsThe thermal decomposition of pre-oxidized polymers is rapid. The majority of the gases is released in thefirst hours. Water and carbon dioxide are the predominant species. Although irradiation reduces the thermalstability of the polymers, our results show that the risk of inflammation is not exacerbated