Two realistic scenarios of intentional release of Radionuclides (Cs-137,Sr-90).The use of the Hot Spot Code to forecast contamination extent.

There are several types of events that could result in dispersion of radioactive substances in the environment. These include both intentional and unintentional events. In case of radiological release the estimation of the area contaminated is a very important point in order to manage the operation needed to decontaminate, the impact on the population and environment and the cost of the decontamination. The extent of the contamination and impact on the environment and people mainly depends on the specific event and the radionuclide involved. In recent years, the concern for protection of urban populations against terrorist attacks involving radiological substances has attracted increasing attention. Models and computational codes have been developed and hypothetical scenarios have been formulated for establishing priority of countermeasures and protective actions, determining of generic operational guidelines, and assessment of risks for population exposure. The aim of the present study is to illustrate the resultant effects of two different cases of intentional release. 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. This is carried out through simulation of different scenarios using a computer code named HotSpot. 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).The 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, similarly 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 depending on particle size, the height of release, and local weather conditions. Key-Words:- Dispersion Models, Radionuclides, Atmospheric Release, Cesium 137, HotSpot code 1 Introduction Incidents involving commercial radioactive sources that have fallen out of control and entered into the public domain have been reported over the years. In some cases, sources entering into scrap processing facilities have