Cesium Emissions from Fires in Contaminated Forest

If a radiological incident such as a nuclear power plant accident, a radiological dispersal device, or detonation of an improvised nuclear device occurs, significant areas may be contaminated. Initial cleanup priorities would likely focus on populated areas, leaving the forested areas to pass several seasons where the overhead canopy materials would fall to the forest floor. In the event of a wildfire in a radionuclide-contaminated forest, some radionuclides would be emitted in the air while the rest would remain in the ash. We report on a laboratory simulation study that examines the partitioning of cesium-133 (a nonradioactive isotope of cesium) between airborne particulate matter and residual nonentrained ash. The experiment was carried out at the Missoula Fire Laboratory combustion chamber. Pine needles were selected as a typical foliage and peat as surrogate for forest duff layer. Three pine needle and three peat (all spiked with CsCl) fires and a blank non-spiked fire of each fuel were conducted. The primary gas emissions were measured as well as size fraction collection of particulates on filters, which were analyzed gravimetrically and for cesium. The residual ash was collected, weighed, and analyzed for cesium. Only 1-2.5% of the spiked cesium in pine needles was emitted as particulate matter, and most of the cesium was concentrated in the particulate fraction greater than 10 μm in aerodynamic diameter. For peat fires, virtually all of the cesium remained in the ash. The results from this study will be used for modeling efforts to assess potential exposure risks to firefighters and the surrounding public.