Evidence of Radiolytic Oxidation of 241Am in Na+ / Cl− / HCO−3/ CO2−3 Media.

Abstract

ABSTRACTThis paper examines Americium behaviour in CI− media at room temperature in connection with environmental and waste disposal programs. Most published values on U, Np, Pu and Am complexation in chloride media have been determined using extraction methods. Spectrophotometric techniques are not sensitive enough to prove actinide complexation by chloride, which is confirmed in this paper for Am(III).Am(OH)3(s), AmOHCO3(s), Am2(CO3)3(s) or NaAm(CO3)2(s) solid phases can control the Am solubility, depending on the chemical conditions of the aqueous phase (usually PCO2). 241Am solubility is here found to be higher in NaCl 4M media than in NaCl 0.1 M (up to 3 orders of magnitude). Addition of a reducing agent (metallic iron) lowers the solubility. After a week, solubilities in NaCl 0.1 M and 4 M are similar. These results are consistent with Am(III) radiolytic oxidation to Am(V), due to cc radiations. Little evidence of Cl− or mixed Cl−-CO2−3 complexes is found in these conditions. In Na+-OH−-Cl− media, 241Am(III) oxidation had also been proposed. Slow kinetics of precipitation could induce experimental uncertainities.