Evaluation of protective measures for tropical environments.

Nuclear and radiological accidents have demonstrated the need for prior planning for exposure assessment as well as guidelines for the implementation of protection and remediation measures of contaminated areas. Typically, the description of the efficiency of the measures in the literature is associated with the reduction of the concentration of the environmental media where they are applied. In order to verify the efficiency related to the reduction in doses, some basic scenarios were established, taking into account aspects of a typical tropical climate, such as building materials (urban areas) and types of crops and farming practices, considering the seasonality and soil type typical of the southeastern region of Brazil. The Integrated System for Emergency (SIEM) program was used to perform the simulations. The results indicate that decision-making processes must be made in accordance with the actual conditions of contamination and use of the affected area. For rural areas, the effectiveness of measures depends on many factors specific to each site, such as seasonality, produced crops, diet habits and degree of subsistence on the items in the diet, which make it unfeasible to develop generic predefined scenarios. The criteria for classification of measurements were defined as: (i) the efficiency in reducing the doses in the first year, in which largest dose rates are observed; (ii) the efficiency in reducing the long-term dose, considering 50 y for adults and (iii) the effect of delay in implementation of the measures on the reduction of doses.

PARATI--a dynamic model for radiological assessments in urban areas. Part III: Parameter uncertainty analysis.

The uncertainties in the exposure predictions after contamination of an urban area due to the variabilities in environmental transfer parameters and in dose conversion factors have been estimated. This was done using the "Latin Hypercube" sampling scheme and the computer codes PRISM and PARATI. For the scenario 'urban contamination by 137Cs' and the population groups considered, the main sources contributing to the uncertainty in the resulting exposures are the limited knowledge of the initial deposition and retention, the weathering processes, the actual urban environments, and the characteristics and habits of the population. The effect of the parameter uncertainties on the variability of the dose is almost constant over time.

PARATI--A dynamic model for radiological assessments in urban areas. Part II. Specifications of individuals and populations, their radiation exposures and variabilities.

After a large-scale contamination of an urban area with gamma-ray emitting radionuclides (e.g. caesium isotopes) decision makers will need guidance as to its potential radiological consequences and to optimum means of mitigation. To provide such information, a dynamic radioecological model PARATI has been developed and used to simulate the contamination of realistic urban environments in a computer model and to estimate the various radiation fields in such environments. In this study, the computer-simulated realistic behaviour and movements of individuals and populations in such radiation fields are described, and the resulting radiation exposures and their variabilities are estimated. For the scenarios considered, the doses of individuals in the same contaminated environment may vary by more than one order of magnitude. Studies on population habits and on the behaviour of radionuclides on important urban surfaces even a long time after the contamination might reduce the uncertainty considerably.

PARATI--a dynamic model for radiological assessments in urban areas. Part I. Modelling of urban areas, their contamination and radiation fields.

The structure and mathematical model of PARATI, a detailed computer programme developed for the assessment of the radiological consequences of an accidental contamination of urban areas, is described with respect to the scenarios used for the estimation of exposure fields in a village or town, the models for the initial and secondary contamination with the radionuclide 137Cs, the concepts for calculating the resulting radiation exposures and the changes with time of the contamination and radiation fields. Kerma rates at various locations in tropical urban areas are given, and the contribution of different contaminated surfaces to these rates after dry or wet deposition are discussed.