Avaliação da concentração de atividade total e da dose como base para requisitos regulatórios de proteção radiológica em instalações mínero-industriais

Abstract

Considering the assumption of risk associated with low doses of ionizing radiation, the National Nuclear Energy Commission (CNEN) published for the first time in 2014 a standard to establish radiological protection requirements for mining and processing facilities for conventional minerals that occur associated with natural radionuclides. According to Standard CNEN-NN-4.01, these facilities are classified into three distinct categories related to the highest concentration of total activity of radionuclides of the uranium and thorium series in the stages of the facility's production process. However, it is questionable whether the activity concentration is a sufficient parameter for defining radiological safety and protection requirements. In this context, the present study aimed to outline the profile of miningindustrial facilities in Brazil and evaluate the total activity concentration and environmental dose as parameters for estimating the potential radiological risk of these facilities. A mixed methodological approach was adopted, comprising quantitative and qualitative analyses, to describe in detail the facilities' characteristics and explore their relationships with the radiological protection requirements established by regulations. The mining and milling facilities were characterized based on data collection from the authorization processes of these facilities with CNEN. RESRAD-OFFSITE software was used to estimate the doses resulting from mining-industrial facilities in individuals from the public, and a correlation analysis was conducted between the dose and the total activity concentration. The results indicated that ten of the 35 facilities had total activity concentrations above 500 Bq/g; nine, between 100 and 500 Bq/g; and sixteen had total activity concentrations below 100 Bq/g and above the exemption limit of 10 Bq/g. Regarding the occupational dose, the results generally indicated low risk in the facilities analyzed. To estimate the dose to the individual member of the public, the information for assessing the environmental radiological impact contained in the processes was insufficient for modeling specific facilities, and a generic simulation was performed indicating, as already presented in the literature, dependence of the dose on the activity concentration and the volume of material. The correlation tests between the occupational dose and the total activity concentration revealed a statistically significant association between them. However, when segmenting the analysis by category, it was noted that only category I (total activity concentrations above 500 Bq/g) demonstrates a statistically significant correlation of moderate magnitude; for the other categories, with concentrations below 500 Bq/g, no statistically relevant correlation was found. Adopting an approach based on total activity concentration and estimated dose to workers and the public may be a more appropriate alternative for regulating mining and milling facilities. Such a strategy would enable more effective regulation, prioritizing situations that most require intervention.