Two realistic scenarios of intentional release of radionuclides (Cs-137, Sr-90) - the use of the HotSpot code to forecast contamination extent

There are several types of events that could result in dispersion of radioactive substances in the environment. The dispersion can be a consequence of a natural or intentional event. In case of radiological release the estimation of the contaminated area is very important to properly manage the rescue operations and decontamination by evaluating the impact on the population and environment. The extent of the contamination and impact on the environment and people mainly depends on the specific event and the radionuclide involved. Models and computational codes have been developed and hypothetical scenarios have been formulated for establishing priority of countermeasures and protective actions, determining generic operational guidelines and assessment of risks for population exposure. The aim of the present study is to illustrate the effects of two different cases of intentional release. Due to the lack of available real data, this is carried out through simulation of different scenarios by using a computer code named HotSpot; in fact literature data referring to real events of this kind are classified and cannot be disseminated. The first case consists in the release of Cs-137 from stacks of cement production industry, the second in the release of Strontium 90 from the explosion of a dirty bomb. The Total Effective Dose Equivalent (TEDE), which includes external and internal contributions for the whole absorbed dose, and the contaminant Ground Deposition have been calculated for various atmospheric stability Pasquill categories [1], several distributions of contaminant particle size, different explosive quantity (dirty bomb case). Results have been analyzed and presented here. They indicate that atmospheric dispersion of a relatively small amount of Cs-137 has the potential to contaminate a relatively large area, while the explosion of a dirty bomb containing a large amount of a strontium 90, does not represent a problem in terms of direct contamination. In both cases the extent of contamination (area and activity) mainly depends on: particle size; the height of release and local weather conditions.