Brian J. Viner

Modelling and mitigating dose to firefighters from inhalation of radionuclides in wildland fire smoke

Firefighters responding to wildland fires where surface litter and vegetation contain radiological contamination will receive a radiological dose by inhaling resuspended radioactive material in the smoke. This may increase their lifetime risk of contracting certain types of cancer. Using published data, we modelled hypothetical radionuclide emissions, dispersion and dose for 70th and 97th percentile environmental conditions and for average and high fuel loads at the Savannah River Site. We predicted downwind concentration and potential dose to firefighters for radionuclides of interest (137Cs, 238Pu, 90Sr and 210Po). Predicted concentrations exceeded dose guidelines in the base case scenario emissions of 1.0 × 107 Bq ha–1 for 238Pu at 70th percentile environmental conditions and average fuel load levels for both 4- and 14-h shifts. Under 97th percentile environmental conditions and high fuel loads, dose guidelines were exceeded for several reported cases for 90Sr, 238Pu and 210Po. The potential for exceeding dose guidelines was mitigated by including plume rise (>2 m s–1) or moving a small distance from the fire owing to large concentration gradients near the edge of the fire. This approach can quickly estimate potential dose from airborne radionuclides in wildland fire and assist decision-making to reduce firefighter exposure.

Intermediate Time-Scale Response of Atmospheric CO2 following Prescribed Fire in a Longleaf Pine Forest

Fire plays an essential role in maintaining the structure and function of longleaf pine ecosystems. While the effects of fire on carbon cycle have been measured in previous studies for short periods during a burn and for multi-year periods following the burn, information on how carbon cycle is influenced by such changes over the span of a few weeks to months has yet to be quantified. We have analyzed high-frequency measurements of CO2 concentration and flux, as well as associated micrometeorological variables, at three levels of the tall Aiken AmeriFlux tower during and after a prescribed burn. Measurements of the CO2 concentration and vertical fluxes were examined as well as calculated net ecosystem exchange (NEE) for periods prior to and after the burn. Large spikes in both CO2 concentration and CO2 flux during the fire and increases in atmospheric CO2 concentration and reduced CO2 flux were observed for several weeks following the burn, particularly below the forest canopy. Both CO2 measurements and NEE were found to return to their pre-burn states within 60-90 days following the burn when no statistical significance was found between pre-burn and post-burn NEE. This study examines the micrometeorological conditions during a low-intensity prescribed burn and its short-term effects on local CO2 dynamics in a forested environment by identifying observable impacts on local measurements of atmospheric CO2 concentration and fluxes.

Radionuclide distribution in soil and undecayed vegetative litter samples in a riparian system at the Savannah River Site, SC

The aim of this study is to comprehensively investigate radionuclide concentrations in surface soil and un-decayed vegetative litter along four stream systems (i.e. Fourmile Branch, Lower Three Runs, Pen Branch, and Steel Creek) at the Savannah River Site (SRS), Aiken, South Carolina. Soil and litter samples from systematically spaced 12 pairs (contaminated or uncontaminated) of plots along the four streams were analyzed for 16 distinct radionuclide activities. Lower radionuclide concentrations were observed in soil and litter samples collected along Pen Branch compared to the other 3 streams. The anthropogenic radionuclide with the highest activity was 137Cs in soil (10.6-916.9 Bq/kg) and litter (8.0-222.3 Bq/kg), while the naturally occurring radionuclides possessing the highest concentration in the samples were 40K (33.5-153.7 Bq/kg and 23.1-56.0 Bq/kg in soil and litter respectively) and 226Ra (55.6-159.9 Bq/kg and 30.2-101.8 Bq/kg in soil and litter respectively). A significant difference (p < 0.05) of radionuclide concentrations between paired-plots across four streams was observed for 241Am, 137Cs, 238Pu, 239Pu, and 226Ra in both contaminated and non-contaminated samples. 137Cs and uranium isotopes had the highest litter-to-soil correlation in contaminated (rho = 0.70) and uncontaminated plots (rho = 0.31-0.41), respectively. 90Sr was the only radionuclide with higher radioactive concentrations in litter (12.65-37.56 Bq/kg) compared to soil (1.61-4.79 Bq/kg). The result indicates that 1) historical discharges of anthropogenic 137Cs was the most important contributor of radiation contamination in the riparian environment at SRS, 2) 90Sr was the only radionuclide with higher concentration in litter than in soil, and 3) no apparent pattern in deposition density in soil or litter along downstream was observed for the radionuclides measured in this study.