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IN-SITU DETERMINATION OF THE EFFECT OF ORGANICS ON THE MOBILITY OF RADIONUCLIDES IN CONTROLLED CONDITIONS GROUNDWATER FLOW

Objective

THE BROAD OBJECTIVE IS TO VERIFY BY MEANS OF IN SITU FIELD TRACER TESTS, PREDICTIONS OF THE MOBILITY OF RADIONUCLIDES IN A SHALLOW GLACIAL SAND AQUIFER, HAVING TAKEN INTO ACCOUNT THE POTENTIAL EFFECTS OF ORGANICS (NATURAL AND INTRODUCED) ON RADIONUCLIDE SPECIATION AND MOBILITY. THE RESULTS WILL BE USED TO IMPROVE THE PREDICTION OF RADIONUCLIDE MIGRATION IN THE GEOSPHERE AND THE OVERALL SAFETY ASSESSMENT OF WASTE DISPOSAL FACILITIES. LIAISON HAS BEEN ESTABLISHED WITH LOUGHBOROUGH UNIVERSITY (LUT) FOR DIRECT SPECIATION MEASUREMENTS, THE UNIVERSITY OF WALES COLLEGE OF CARDIFF UWCC (FORMERLY INSTITUTE OF SCIENCE AND TECHNOLOGY (UWIST) FOR RADIONUCLIDE SPECIATION MODELLING, AND DELFT GEOMECHANICS FOR SOLUTE TRANSPORT MODELLING.
2 tracer tests with conservative species have been carried out in a shallow glacial sand aquifer. The transport properties of the aquifer were determined in order to compare the use of the 3 conservative tracers (chloride as sodium chloride, iodine-131 as potassium iodide and tritium as HTO) and to provide a reference for further experiments involving chemical reactive solutes.

A 2-dimensional layered model was used to estimate the hydraulic conductivity of each layer from the tracer breakthroughs. A 1-dimensional analytical solution to the advection dispersion equation was used to estimate the dispersion lengths of each layer. Longitudinal dispersion lengths ranged from 0.5 to 5 cm, 50-150 times less than the path length. The aquifer properties were slightly altered by the running of the tests.
THE PROJECT IS DIVIDED INTO A NUMBER OF RESEARCH AREAS AS FOLLOWS :

- AQUIFER CHARACTERISATION AND INSTRUMENTATION - INVOLVES THE DETERMINATION OF AQUIFER HYDRAULIC PROPERTIES, ITS GEOCHEMISTRY, MINERALOGY AND GROUNDWATER COMPOSITION, PARTICULARLY THE NATURE AND AMOUNTS OF NATURAL ORGANICS (HUMIC AND FULVIC ACIDS) AND COLLOIDS. DEVELOPMENT OF INSTRUMENTATION TO MONITOR GROUNDWATER COMPOSITION AND RADIONUCLIDE MIGRATION.

2) CHARACTERIZATION OF COMPLEXES AND COLLOIDS - INTERLABORATORY COMPARISON WITHIN THE CEC, TO CHARACTERISE, AND DETERMINE STABILITY CONSTANTS WITH SELECTED RADIONUCLIDES, FOR COMMERCIALLY AVAILABLE HUMIC ACID AND NATURAL ORGANICS FROM DRIGG, MOL, ISPRA ETC. A PARALLEL EXCERCISE IS UNDERWAY FOR COLLOIDS.

3) LABORATORY SORPTION STUDIES - WILL INCLUDE BATCH SORPTION EXPERIMENTS TO DETERMINE THE EFFECTS OF NATURAL ORGANICS ON RADIONUCLIDES SORPTION, KINETIC MEASUREMENTS, AND DIRECT SPECIATION DETERMINATIONS ATTEMPTED ON RADIONUCLIDES IN GROUNDWATER AFTER EQUILIBRATION WITH THE SEDIMENT.

4) MODELLING - SPECIATION MODELS WILL BE USED TO PREDICT THE SPECIATION OF RADIONUCLIDES IN THE SORPTION EXPERIMENTS AND HELP TO DETERMINE THE IMPORTANT MOBILE SPECIES IN THE FIELD TEST. DETERMINISTIC FLOW MODELLING WILL AID IN THE DESIGN OF THE BOREHOLE ARRAY FOR THE TRACER TESTS AND FORM A BASIS FOR REACTIVE MASS TRANSPORT MODELS.

5. FIELD TRACER EXPERIMENTS - INITIAL TRACER TESTS WILL COMPARE VARIOUS CONSERVATIVE TRACERS (131 I, CL AND 3H) AND PROVIDE BACKGROUND DATA ON THE HYDRAULIC CHARACTERISTICS OF THE AQUIFER. SUBSEQUENT TRACER TESTS WILL INVOLVE REACTIVE RADIONUCLIDE SPECIES WITH THE ADDITION OF ORGANIC SOLUTES.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

Natural Environment Research Council
Address

NG12 5GG Nottingham
United Kingdom