Fate and transport of radiocesium in urban building materials

Abstract

Fine radioactive particulate dispersal in outdoor areas presents significant economic, social, environmental and public health concerns. The interactions of these radioactive particles with urban surfaces need to be well understood to develop optimized decontamination strategies. The major environmental factors influencing these interactions are relative air humidity, temperature and rain. The objective of this work is to investigate the fate and transport of water soluble cesium deposited on conventional urban building materials, especially concrete, brick, asphalt, limestone, and granite, under various environmental conditions (relative humidity (RH), and atmospheric precipitation). The data on the kinetics of ¹³⁷Cs desorption from building materials by the solution containing 100 mM of Ca²⁺ and 0.5 mM of K⁺ have shown that the shape of the ¹³⁷Cs desorption curves is similar for all building materials. There is a rapid initial decrease in the activity of the sorbed ¹³⁷Cs. The desorption rate first decreases quickly during 7–10 days and practically does not change later. The remaining ¹³⁷Cs in building materials that is not desorbed by the solution is 30-40% of the initially sorbed amount. For the building materials of interest, radiocaesium interception potentials (RIP). The RIP(K) value has been shown to range from 20 to 300 mM/kg and increase in the order: limestone > brick > concrete > granite > asphalt. The fine fraction of building materials (<0.125 mm) sorbs ¹³⁷Cs better than the coarse fraction (0.0125–0.25 mm). Based on RIP(K) value and measured concentration of cations the distribution coefficients K_d(¹³⁷Cs) were determined. The study of the mechanisms of radiocesium binding by different components of building materials, based on sequential extraction technique, shows that the highest ability to bind ¹³⁷Cs is characteristic of asphalt which retains 40.9±1.0 % of ¹³⁷Cs after all extractions. By the ability to bind ¹³⁷Cs with the residual fraction, the studied materials form the following sequence: concrete > limestone > granite > brick. Method to study radionuclides distribution in depth of building materials using layer-by-layer grinding has been developed.