Uncertainties in the use of concentration ratios for modelling NORM waste sites. (October 2020)

• Record Type: Journal Article
• Authors: Kaasik, Marko; Mora, Juan C.; Vives i Batlle, Jordi; Vanhoudt, Nathalie; Tkaczyk, Alan H.
• Is Part Of: Journal of environmental radioactivity. Volume 222(2020)
• Publication Date: 2020-10
• Subjects: Naturally occurring radioactive material (NORM) -- Calcium fluoride -- Radionuclides -- Radioecological model -- Soil -- Pine tree; Radioactivity -- Periodicals; Radiation, Background -- Periodicals; Radioecology -- Periodicals; Radioactive pollution -- Periodicals; Environmental Pollutants -- Periodicals; Radioactive Pollutants -- Periodicals; Radioactivity -- Periodicals; Radioécologie -- Périodiques; Pollution radioactive -- Périodiques; Fond de rayonnement -- Périodiques; 539.752
• DOI: 10.1016/j.jenvrad.2020.106315
• Languages: English
• ISSNs: 0265-931X

Abstract

Abstract: The activity concentrations of 238 U, 226 Ra and 210 Pb were modelled in Pinus sylvestris (Scots pine trees) on a uniform CaF2 sludge heap in Belgium. The aim of this work is to enhance the knowledge of how transfer factors behave in NORM landfills. The simplest possible model in radioecology is used, which is based on Concentration Ratios (CR-s) measured in equilibrium and activity concentrations of the above-mentioned radionuclides measured in the substrate where pine trees grow. Two alternative CR-s were used: (1) international CR compilations by the IAEA (2014) and (2) CR-s specifically determined for pine trees studied in British Columbia (Mahon and Mathews, 1983). Both CR-s were applied assuming lognormal distributions fitted from data reported in the literature. The results were compared with activity concentrations measured in trees sampled on-site. Modelled concentrations match the measured ones best in the case of 238 U. For the studied NORM waste site, the approach using generic IAEA concentration ratios does not fulfill the conservatism requirement in the cases of 238 U and 226 Ra, as the concentration of radionuclides in trees is underestimated. On the other hand, the ratios from Mahon and Mathews, (1983) produce wide distributions, ensuring conservatism due to larger CR-s. The measured concentrations are narrowly distributed in general, which can be expected on a small sampling site on a uniform substrate. The generic approach outlined here is practical but, as a result of the uniqueness of the site considered, should be applied cautiously in other NORM situations. Highlights: Generic IAEA CR-s lack conservatism for 238 U & 226 Ra with CaF2 as growth substrate. Conservatism due to wider distribution for CR-s derived from Pinus contorta trees. Generic CR approach should be applied cautiously in NORM situations.