Euradwaste '08 - EU Bookshop - Europa

materials. For attaining the stated goal, different materials may be used. In this work several commercial
IER with high thermal, chemical and radiation stability were chosen. The conditions for
production of the carbon matrices incorporating rhenium, stable iodine and stable europium as the
chemical analogues of 99 Tc, 129 I and 241 Am, respectively, were investigated.
2. Methodology
2.1 Initial materials and reagents
Polyimide binder ITA-31 with the following composition was used: dianhydride of 3,3 / ,4,4 / -benzo-
phenonetetracarboxylic acid - 50% and tetraacetyl derivative of 4,4 / -diaminodiphenyl ether - 50%.
During composite synthesis the binder was mixed with IER containing rhenium in the form of perrhenate-ion
(ReO4 - ), iodine in the form of iodide-ion (I - ) and europium in the form Eu +3 . The
strongly basic anionites like AV-17, VP-1AP, VPB, Amberlite IRA-400 and Dowex 1×4 were used
for preliminary sorption of rhenium and iodine. For preliminary sorption of europium the Russian
IER SF-5 and KB-10 were applied. The carbon fabric of ELUR type was used in composite synthesis
as reinforcing addition for higher strength of matrices.
2.2 Synthesis of composites and their carbonization
Synthesis of composites was carried out in two stages [5]. At the first stage the composite-1 incorporating
ITA-31 binder and the IER containing a corresponding nuclide at the ratios of ITA-31:IER
8:1 ÷ 1:1 was synthesized. ITA-31 and IER were mixed at 260 – 280°�. Then the carbon fabric
ELUR was added to the resultant composite-1 for its higher strength to afford its mass content from
20 to 60% in end product (composite-2). The process for production and pressing of composite-2
was conducted at 280-320°� and under excess pressure of 20 – 250 atm., while the carbonization
process proceeded at 600 – 650°�.
2.3 Determination of leach rates
The procedures recommended by International standards were used for determination of leach rates
of rhenium, iodine and europium from obtained matrices [6-7]. ICP MS and emission spectral
analysis was used for determining I, Re and Eu leach rates.
3. Results
3.1 Thermal stability of composites
Taking into account that the radioactive waste containing long-lived radionuclides may be heatedup
due to radioactive decay, special attention should be given to thermal resistance of matrices used
for long-term storage or final disposal of RAW. In the previous works conducted by the authors it
was shown that the carbonization process of the composites containing polyimide binders is an efficient
method for production of heat-resistant carbon-plastics and carbon-carbon materials on their
basis [4]. However, it was unknown which properties would be typical for the composites based on
ITA-31 and other components of produced matrices. Such components may involve, for instance,
the IER containing the elements under investigation. In the early stage of investigations some experiments
to measure thermal resistance of initial components and related composites were performed.
In Fig. 1 the data are given of differential thermogravimetric analysis (DTA) of VP-1AP in
different chemical forms, including that containing the stable iodine as I - . For correlation purposes
there are also presented the DTA individual results on the ITA-31 and composite containing ITA-31
and VP-1�P in I - - form.
416