Decontamination after a nuclear or radiological release requires a detailed understanding of the materials hosting the contamination, the chemistry of the radionuclide, and the chemical properties of the decontamination agent. Urban contamination via a number of radiological release scenarios may require simple decontamination methods that can be deployed for wide-area decontamination. This paper investigates a number of factors of importance for developing such decontamination methods, focusing on cesium. These factors include the influence on decontamination approaches from the cesium deposition conditions, the urban building material composition and, when washing with an ionic solution that is utilized for decontamination, the composition of the wash solutions. In summary, the sorption chemistry of cesium onto urban building materials and roadways has been studied to develop simple decontamination methods that can be deployed for wide-area decontamination efforts.To improve the understanding of the sorption of cesium onto common urban building materials and roadways the desorption of cesium deposited from solution and as a dry powder was tested. Using ammonium (NH 4 + )salt solutions, we tested the desorption of ionic cesium bound to individual components of concrete and coupons of several common building materials. While the tests on concrete aggregate suggest that a concentration >10 mM NH 4 + does not improve the desorption of cesium, tests on concrete, asphalt, marble, limestone and granite monoliths showed improved decontamination factors when the NH 4 + concentration increased from 0.1 to 0.5 M. We also found that cesium as dry particulate material could be removed quite effectively although the contamination became tenacious upon wetting the surface.

No abstract

To support the viability of a wash-down approach to mitigating nuclear contamination, this study presents a characterization of the aggregate of a common concrete by optical microscopy and the sorption-desorption characteristics of cesium from these into potential wash solutions. Various minerals with weathered surfaces displayed strong affinity for 137Cs with an effective partition coefficient Kd=120 mL/g for micas,>25-90 mL/g for feldspars, and>25-30 mL/g for amphiboles. The desorption Kd into 0.1M NH 4 Cl varied greatly but for amphiboles, sandstones, granite, and fine-grained quartzite it was>200 mL/g as a result of irreversible sorption. These same mineral phases are prevalent in all types of building materials, extending our conclusions more broadly to the problem of wide-area urban decontamination. In contrast, ionic solutions desorbed up to 98% of 137 Cs from cement, suggesting that fresh concretes with an intact surface layer of cement could be more easily decontaminated if Cs + interactions with the underlying minerals could be avoided. For practical applications common, non-hazardous chemicals such as sodium, potassium, and ammonium salts are as effective or more effective than harsher chemicals and expensive chelating agents. For example, when treated shortly after exposure, on timescales commensurate with early response phase activities, 0.5M KCl could remove nearly 50% of bound 137 Cs from concrete aggregate. Statistical analyses showed that desorption from the fine aggregate benefited from higher K + and NH 4 + concentrations. These results suggest that contamination in large areas of the urban environment can be dramatically reduced using common chemicals obtained readily from local stores.

No abstract

Volume of 1.0 M HNO 3 needed to adjust pH of unbuffered clay slurry. The corresponding concentration of protons for an unbuffered solution is given in the bracketed abscissa labels.