Variation of natural radionuclides in non-ferrous fayalite slags during a one-month production period.

The European Basic Safety Standards (EU-BSS) describes a set of NORM (Naturally Occurring Radioactive Material)-processing industries which produce residues known to be possibly enriched in NORs (Naturally Occurring Radionuclides). These residues can be used as a component in building materials aimed for public usage. The industrial processes, in which the residues are produced, are often complex and total monitoring can be challenging especially when the origin of the used raw materials varies. In this study the NORs present in non-ferrous fayalite slags of a secondary smelter facility, a NORM-processing industry according to the EU-BSS, were monitored daily during a one-month production period. In addition flue dust samples and feedstock samples, known to contain elevated levels of NORs, of the same period were measured. The survey involved the gamma-ray spectrometric analysis of the decay products from the 238U and 232Th decay chains, 235U and 40K using HPGe detectors. Secular equilibrium was observed for the slags, flue dust and feedstock samples in the 232Th decay chain, in contrast to the 238U decay chain. During the month in question the ratios of maximum over minimum activity concentration were 3.1 ± 0.5 for 40K, 4 ± 1 for 238U, 6 ± 1 for 226Ra, 13 ± 7 for 210Pb, 4.5 ± 0.6 for 228Ra and 4.7 ± 0.7 for 228Th for the slags. Even with the activity concentration of the feedstock material ranging up to 2.1 ± 0.3 kBq/kg for 238U, 1.6 ± 0.2 kBq for 226Ra, 22 ± 7 kBq/kg for 210Pb, 2.1 ± 0.2 kBq/kg for 228Ra and 2.0 ± 0.4 kBq/kg for 228Th, none of the slag samples exceeded the exemption/clearance levels of the EU-BSS and RP-122 part II, which can respectively provide guidance under equilibrium and in absence of equilibrium. As each NORM-processing industry has its own complexity and variability, the observed variations point out that one should approach one-time measurements or low frequency monitoring methods cautiously. Low frequency measurements should be optimised depending on the discharge of the batches. A follow up of the industrial process and its output can provide important insights to assure a limited public exposure upon application of these industrial residues. Finally a comparison is made with reported data on other metallurgical slags and the use of the slags in building materials is evaluated using the Activity Concentration Index (ACI) proposed by the EU-BSS.

Radiological characterization and evaluation of high volume bauxite residue alkali activated concretes.

Bauxite residue, also known as red mud, can be used as an aggregate in concrete products. The study involves the radiological characterization of different types of concretes containing bauxite residue from Ukraine. The activity concentrations of radionuclides from the 238U, 232Th decay series and 40K were determined for concrete mixture samples incorporating 30, 40, 50, 60, 75, 85 and 90% (by mass) of bauxite residue using gamma-ray spectrometry with a HPGe detector. The studied bauxite residue can, from a radiological point of view using activity concentration indexes developed by Markkanen, be used in concrete for building materials and in road construction, even in percentages reaching 90% (by mass). However, when also occupational exposure is considered it is recommended to incorporate less than 75% (by mass) of Ukrainian bauxite residue during the construction of buildings in order to keep the dose to workers below the dose criterion used by Radiation Protection (RP) 122 (0.3 mSv/a). Considering RP122 for evaluation of the total effective dose to workers no restrictions are required for the use of the Ukrainian bauxite residue in road construction.