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LIMITING SOLUBILITIES OF RADIOELEMENTS IN THE INETRSTITIAL WATERS OF ADJACENT AND BACKFILLING MATERIALS FOR WASTE STORAGE.

Objective

THE SAFETY STUDIES ON SITES FOR THE STORAGE OF NUCLEAR WASTE RELY ON THE MODELLING OF RADIOLELEMENT MIGRATION PATTERNS UNDER THE HYDROLOGICAL AND CHEMICAL CONDITIONS OF THE NATURAL ENVIRONMENT (FAR FIELDS) STARTING FROM A "SOURCE OF RADIOACTIVITY" REPRESENTED BY THE WASTE ITSELF. IN VIEW OF THE COMPLEXITY OF THE PHENOMENA INVOLVED, OUR AIM SHOULD BE TO FIND REALISTIC SIMPLIFICATIONS WHICH, WHILE OFFERENG GUARANTEES AS TO THE MAXIMUM LEVEL OF RADIOACTIVITY RELEASED, DO NOT LEAD TO AN EXAGGERATED ASSESSMENT OF THE RISK.

THE FOLLOWING SIMPLIFIED SCENARIO WILL BE ADOPTED:

- THE HYDROLOGICAL MOVEMENTS ARE SUFFICIENTLY SLOW TO ENSURE THAT THE INGRESS OF WATER AT THE STORAGE SITE IS IN EQUILIBRIUM WITH THE CONSTITUENT MATERIALS;

- THE CHEMICAL PARAMETERS OF THIS SOLUTION IMPOSE A LIMITING SOLUBILITY FOR EACH RADIOELEMENT.

THIS APPROACH WILL HAVE THE ADVANTAGE OF PROVIDING AN ESTIMATE OF THE UPPER LIMIT OF THE RADIOACTIVITY RELEASED BY STORED NUCLEAR WASTE ON THE BASIS OF A SIMPLE AND REALISTIC SCENARIO.
The migration of actinides inside cement (or concrete) is very slow, even when the material is saturated with water. Precipitation of actinide hydroxide explains this retention phenomenon.
This work measures americium solubility in aqueous solutions equilibrated with CPA55 cement to:
compare it, with thermodynamic predictions;
correlate it to migration measurements of americium through cement discs.
THE AIMS OF THE RESEARCH WILL BE TWOFOLD:

- TO DEFINE THE CHEMICAL CONDITIONS: WE NEED TO KNOW AS MUCH AS POSSIBLE ABOUT THE CHEMICAL COMPOSITION OF THE WATERS IN EQUILIBRIUM WITH THE STORAGE MATERIALS (BARRIERS, BACKFILLERS) IF NECESSARY BY MEANS OF EXPERIMENTAL MEASUREMENTS OF THE STATIC LEACHING OF THESE MATERIALS.

- TO FIND THE LIMITING SOLUBILITY OF THE RADIOELEMENTS (ESSENTIALLY ACTINIDES) IN THESE WATERS, EITHER BY CLACULATION OR BY EXPERIMENT. IT WILL THEREFORE BE NECESSARY TO FOCUS ON THE FOLLOWING:

- THOSE OF THE CHEMICAL REAGENTS PRESENT (RELEASED BY THE MATERIALS) THAT ARE LIKELY TO REACT WITH THE RADIOELEMENTS;

- THE SOLIDS FORMED (BY PRECIPITATION AND COPRECIPITATION);

- THE SOLUBLE COMPLEXES.

DATA BASES CREATED OUTSIDE THE FRAMEWORK OF THIS STUDY WILL BE USED FOR THE PURPOSES OF THIS APPLICATION.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

Commissariat à l'Energie Atomique (CEA)
Address
Centre D'études De Fontenay-aux-roses
92265 Fontenay-aux-roses
France