Neptunium Migration in Oxidizing Clayey Sand

Abstract

THE RATE AND MECHANISM OF NEPTUNIUM MIGRATION WERE INVESTIGATED IN A FLOWING WATER/CLAYEY SAND SYSTEM UNDER OXIDIZING CONDITIONS. A 237 NP-DOPED BOROSILI- CATE GLASS WAS USED AS A SOURCE OF CONTAMINANT IN THE MIGRATION EXPERIMENTS. A PRELIMINARY STUDY OF THE CHEMICAL SPECIATION OF NEPTUNIUM IN THE WATER LEACHATE ALLOWED TO IDENTIFY SOLUBLE CATIONIC AND ANIONIC CARBONATE SPECIES OF NP(V). INCREASING CARBONATE CONCENTRATION IN THE SOLUTION RESULTED IN A DECREASE OF THE AMOUNT OF NEPTUNIUM SORBED ON THE SAND. YET SUCH A DECREASE IS LOWER THAN THAT CALCULATED ASSUMING THE UPTAKE OF THE CATIONIC SPECIES. THIS WAS INTERPRE-TED AS A SIMULTANEOUS SORPTION OF NPO+2 AND NOP2(CO3)-. A KINETIC MODEL INCLU- DING RAPID SORPTION REACTIONS AND A SLOW INTERCONVERSION BETWEEN NPO+2 AND NPO2(CO3)-WAS DEVELOPED. ANALYTICAL SOLUTIONS OF THE TRANSPORT EQUATION WERE USED FOR BEST FIT ANALYSIS OF THE NEPTUNIUM COLUMN PROFILES. BOTH THE SORPTION REACTION AND THE DISSOCIATION KINETICS WERE CONSIDERED IN THE MODEL.NA - NOT AVAILABL