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SOLIDIFICATION OF TRU-WASTE BY EMBEDDING IN A CERAMIC MATRIX.

Objective

CERAMIC MATERIALS ARE EVALUATED AS A MATRIX FOR TRU-WASTES,I.E DISSOLVER RESIDUES FROM REPROCESSING, LIQUID ALPHA CONCENTRATES FROM FUEL ELEMENT FABRICATION, RESIDUES FROM THE DRY INCINERATION AND FROM THE ACID DIGESTION OF TRU-WASTES, AS WELL AS ACTINIDE SLUDGES PRECIPITATED FROM MAW-SOLUTIONS.
CLAY MINERALS (BENTONITE AND KAOLINITE) AND REACTIVE CORUNDUM ARE PREFERENTIALLY SELECTED AS RAW MATERIALS FOR THE SOLIDIFICATION OF THESE WASTES.THE MAIN PROCESS STEPS ARE:1) PRETREATMENT OF THE WASTE,
2) MIXING WITH CERAMIC RAW MATERIALS,
3) FORMING BY EXTRUSION,
4) DRYING AND SINTERING WITH TMAX=1300 DEG.C FOR ABOUT 10 MINUTES.

THIS WAY OF TRU-WASTE IMMOBILIZATION HAS BEEN DEMONSTRATED USING ALL KINDS OF ORIGINAL TRU-WASTE KNOWN ON LAB-SCALE.THE LEACH RATE FOR ACTINIDES IS LESS THAN 10 POWER TO 8G/CM TO THE SQUARE D IN WATER AND SALT BRINES AT ROOM TEMPERATURE, THE AVERAGE OPEN POROSITY < 5 VOL%, THE COMPRESSIVE STRENGTH> 50 N/MM TO THE SQUARE.

AIM OF THE CURRENT PROGRAMME IS TO ACHIEVE A SIGNIFICANT VOLUME REDUCTION OF THE FINAL PRODUCT BY APPLYING THE POTENTIAL OF THE CERAMIC MATRIX EG BY:
1) INCREASING THE WASTE LOADING (20 WT.-%) AND,
2) BY SIMULTANEOUS CERAMIZATION OF SEVERAL WASTE STREAMS.
Aluminium silicate based ceramic materials have been evaluated as an alternative waste form for the incorporation of TRU wastes. These waste forms are free of water and cannot generate hydrogen radiolytically, show good compatibility between the compounds of the waste and the matrix and are resistant against aqueous solutions, heat and radiation. The main process steps are pretreatment of the liquid waste (concentration, denitration, neutralisation, solid-liquid separation), mixing with ceramic raw materials and forming, and heat treatment with maximum temperature of 1300 C for 15 minutes.

Aluminium silicate based ceramic materials have been evaluated as an alternative waste form for the incorporation of TRU wastes. These waste forms are free of water, cannot generate hydrogen radiolytically, show good compatibility between the waste compounds and the matrix, and are resistent to aqueous solutions, heat and radiation.

The specific alpha activity of the TRU waste ceramics range between 6E-7 and 2.2E-9 Bq/g. As revealed by means of optical and scanning electron microscopy, the waste particles, mostly TRU oxides, noble metals and oxides, are bonded tightly as inclusions within the fine grained matrix (grain size < 10 um).

An attempt was made to produce ceramics on a technical scale under conditions of remote operation. The quality of TRU waste ceramics produced on a semitechnical scale corresponded to that of the laboratory scale specimens.

TRU waste ceramisation offers the options of high waste loadings (> 20 weight %) as well as simultaneous ceramisation of several waste types. This may contribute significantly to reducing waste volume.
B.1. DETERMINATION OF THE MAXIMUM WASTE LOADING FOR THE ALUMOSILICATE CERAMIC MATRIX WITH DISSOLVER RESIDUES; CHARACTERISATION OF THE FINAL PRODUCTS.

B.2. DETERMINATION OF THE MAXIMUM WASTE LOADING FOR THE ALUMOSILICATE CERAMIC MATRIX; CHARACTERISATION OF THE FINAL PRODUCTS WITH TRU-ASHES.

B.3. DETERMINATION OF THE MAXIMUM WASTE LOADING FOR THE ALUMOSILICATE CERAMIC MATRIX WITH SLUDGES,PRECIPITATED FROM ACID DIGESTION SOLUTIONS; CHARACTERISATION OF THE FINAL PRODUCTS.

B.4. DETERMINATION OF THE MAXIMUM WASTE LOADING FOR THE ALUMISILICATE CERAMIC MATRIX WITH SLUDGES, PRECIPITATED FROM TRU-SOLUTIONS OF THE FUEL ELEMENT FABRICATION; CHARACTERISATION OF THE FINAL PRODUCT.

B.5. CERAMIZATION OF TRU-WASTE-MIXTURES,ACCORDING 1-4; CHARACTERISATION OF THE FINAL PRODUCTS.

B.6. DEVELOPMENT OF A TECHNICAL PROCESS FOR THE CERAMIZATION OF TRU-WASTE.CONSTRUCTION OF A PILOT PLANT.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

Forschungszentrum Karlsruhe Technik und Umwelt GmbH
Address

76021 Karlsruhe
Germany