Reaction Pathways of Plutonium andNeptunium in Selected Natural Water Environments

SURFACES OF SOLIDS IN NATURAL WATERS ARE THE SITES OF IMPORTANT GEOCHEMICAL PROCESSES CONTROLLING THE FAR-FIELD IMPACT OF A NUCLEAR WASTE REPOSITORY. GIVEN THE COMPLEXITY OF THE SYSTEMS UNDER INVESTIGATION, IT IS NOT POSSIBLE TO QUANTITATIVELY DESCRIBE THESE PHENOMENA WITHOUT A KNOWLEDGE OF THE CHEMICAL SPECIATION OF RADIONUCLIDES AND THEIR RESIDENCE TIMES. IN THIS PAPER, THE RE- SULTS OF EXPERIMENTS TO DETERMINE THE EFFECTS OF VARIATIONS OF EH, IONIC STRE- GTH AND ORGANIC MATTER ON THE MOBILITY OF NEPTUNIUM AND PLUTONIUM IN SEDIMENTS OF DIFFERENT ORIGIN ARE PRESENTED. IONIC STRENGTHS HAVE BEEN CHOSEN TO ENCOM- PASS THE RANGE OF SALINE WATERS SURRONDING SALT FORMATIONS WHICH PROVIDE A FAVOURABLE EXAMPLE OF THE VARIABILITY EXISTING IN NATURAL AQUATIC ECOSYSTEMS. MOBILITY CHANGES OBSERVED AT HIGH SALINITIES REFLECT THE INTERACTION OF COMPE- TITIVE CATIONS. SPECIATION STUDIES PROVIDED DIRECT EVIDENCE FOR NP(V) COMPLE- XATION EVIDENCE WITH CARBONATES. THESE SPECIES HAVE BEEN SHOWN TO PARTICIPATE IN THE NEPTUNIUM FIXATION REACTIONS IN GROUNDWATERS CONTAINING CARBONATES. IN GENERAL, THE DEVELOPMENT OF REDUCING ENVIRONMENTAL CONDITIONS HAS BEEN FOUND TO DECREASE THE TRAVEL DISTANCE COVERED BY THE RADIONUCLIDES.

BIDOGLIO Giovanni;  AVOGADRO Alessandro;  DE PLANO Alfonso;  LAZZARI Giampietro; 

1995-03-15

JRC5185

https://publications.jrc.ec.europa.eu/repository/handle/JRC5185,