The use of macrocyclic polyethers for promoting the dry cleaning of the surface from radionuclides

The cleaning of the stainless steel surface from Cs-137 and Sr-90 ions was studied by the peelable polymer film method. An extracting solution of polyvinylbutyral in dioxane containing various crown ether additions to increase the efficiency of extraction was spread over the surface. A polymer film formed on the surface as a result of solvent evaporation from the extracting solution. After the extraction, the polymer film containing radionuclides was removed and utilized. The extraction of Cs-137 and Sr-90 ions from neutral aqueous solutions with AN-221 and AN-511 anionites modified with crown ethers was studied. The distribution coefficients were shown to increase in the series 12-crown-4 < 18-crown-6 < dicyclohexyl-18-crown-6 < 15-crown-5 for the extraction of Cs-137 and in the series 15-crown-5 < dicyclohexyl-18-crown-6 < 18-crown-6 < 12-crown-4 for the extraction of Sr-90. The structural characteristics of the Cs and Sr complexes with crown ethers taken from the Cambridge Structural Database (2013 Release) were compared with the data on the extraction of Cs-137 and Sr-90 ions from aqueous solutions. The distances between the two complexing atoms (O-Cs or O-Sr) decreased as the corresponding distribution coefficients increased. The dependences of the residual radioactivity (Cs-137 and Sr-90) on the number of depositions/removals of the polymer film on/from the surface were measured for different crown ethers. When crown ethers were added to the extracting solution (polymer film), the efficiency of decontamination increased by two orders of magnitude. The most effective additions were dicyclohexyl-18-crown-6 and 15-crown-5 for Cs-137 and 12-crown-4 for Sr-90. After three treatments of the surface with solutions (polymer films) with these additions, its radioactivity was close to background.