Conditional stability constants have been determined for U(IV) and U(VI) Boom Clay humic acid (BCHA) and Aldrich humic acid
(AHA) complexes, under anaerobic and carbonate free conditions. The constants are needed for nuclear waste repository performance
assessment purposes. The U(IV) constants were obtained by developing an approach based on the solubility product of amorphous
U(OH)4. The U(VI) constants were obtained by applying the Schubert ion-exchange approach.