Long-term prediction of non-processed waste radioactivity of a niobium mine in Brazil

Abstract

This work analyzed samples from a niobium mine in Brazil which produces massive quantities of non-processed waste (NPW) each year. Due to concerns about the environmental impact of stacking up this material in the longterm, investigations have had been made to evaluate its re-use options. Nevertheless, there are no regulations from the Brazilian National Commission of Nuclear Energy about commercializing this sub-product which has highly variable radiological activity because of the different lithologies present in the mine. Thus, the activity concentrations of 238U, 232Th, 226Ra, 228Ra, 228Th and 40K of the naturally radioactive ore (53 boreholes) and of the NPW (8 samples) were measured. Radiological hazard indices, radium equivalent, internal and external hazard and their equivalent doses were also calculated. Moreover, the X-ray diffraction, depth and coordinates of all samples were used to identify radioactive prone areas in the mine. For the NPW samples, the activity concentrations (in Bq/kg) were, on average, 64.9 of 238U, 104.8 of 226Ra, 1813.9 of 232Th, 1292.2 of 228Th, 1224.3 of 228Ra and 1184.2 of 40K. The analysis showed great variability between samples and the results can be used to evaluate possible uses such as building materials or foundation for roadbeds.