Cesium emissions from laboratory fires

Abstract

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. This paper reports 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 when pine needles and peat are doped with cesium. Only 1-2.5% of the doped 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.Implications: There is a potential for emissions of radionuclides such as cesium-137 from a wildfire over a radionuclide-contaminated forest. This paper reports on a laboratory simulation study of a wildfire with two types of biomass doped with nonradioactive cesium. This simulation suggests that only 1-2.5% of the cesium in the biomass will be emitted from the wildfire, while the rest will reside in the residual ash. In this study, pine needles were the only contributor to the air emissions of cesium; duff was not a source of cesium emissions. In this study, cesium emitted from the simulated wildfire was concentrated in the particle sizes larger than 10 µm.

Uncovering transport, deposition and impact of radionuclides released after the early spring 2020 wildfires in the Chernobyl Exclusion Zone

“…It is noteworthy that stations close to the CEZ are captured by the model effectively and in some cases are overestimated, whereas stations far from the source are underestimated. This indicates that the assumption that exactly 60% of the particles was released in sizes > 10 μm following previous research 12,15,30 is probably inaccurate. The size distribution has been found to depend on the type of the biomass burned and the type of fire (smoldering, flame or mixed) 31 .…”

“…To estimate the model sensitivity of the aforementioned factors that have caused biased concentrations and considering that the model does not account for wind resuspension, we calculated the uncertainty of transport and deposition of 137 Cs after the April 2020 fires in the CEZ. For this, a model ensemble that consists of three simulations with different emissions (709, 249 and 46 GBq) was used, 10 combinations of mass fraction per particle size, for each of them, always following the recommendation of Hao et al 30 that the majority of the emitted particles is at sizes > 10 μm (Table S2), and five different EFs (Table S3); this gives a total number of 150 (3 × 10 × 5) ensemble members. The model uncertainty ( Fig.…”

“…4) was calculated as the standard deviation of 137 Cs deposition resulting from all ensemble members. Model uncertainty appears to be about 70% near the source and increases with distance due to the focus on large particles 30 . Large particles deposit nearby due to www.nature.com/scientificreports/ gravitation and less likely reach center or west of Europe.…”

“…Then, we use the most recently updated emission factors (EFs) for radionuclides released from wildfires 30 together with ground contamination data [49][50][51] from the CEZ ( Figure S3, Figure S4). Method 2 (top-down) combines EFs of 137 Cs (in gr species per kg of dry mass burned) from Hao et al 30 with combusted biomass (in kg of dry mass) from Copernicus Atmosphere Monitoring Service (CAMS) Global Fire Assimilation System (GFAS) 52 ( Figure S4a). Finally, Method 3 (top-down) uses experimental ratios of 137 Cs with particulate organic matter (POM) from Strode et al 53 for boreal regions and calculates emissions using POC from CAMS GFAS 52 ( Figure S5b).…”

“…It has been previously shown that labile 137 Cs and 90 Sr radionuclides are attached to sub-micron aerosol particles (< 1 μm) 61 , whereas refractory 238 Pu, 239 Pu, 240 Pu and 241 Am are PM10 particles 62 . Recently, Hao et al 30 reported that 137 Cs released from laboratory fires was concentrated in the particulate fraction greater than 10 μm. To capture the reported size variability, we simulated all six species with a size distribution (characterised by a species diameter normalized logarithmic standard deviation 57 ) around particle sizes of 0.25, 8 and 16 μm.…”