Abstracts and Available Papers Presented at the
2002 International RERTR Meeting

IMMOBILIZATION OF PRECONDITIONED SPENT FUEL FROM NUCLEAR RESEARCH REACTORS IN A CERAMIC MATRIX

Diego.O. Russo, Diego. S. Rodríguez, Arturo D. Heredia, Miguel Sanfilippo,

Mario E. Sterba, Patricia Mateos

Comisión Nacional de Energía Atómica - Centro Atómico Bariloche – Bariloche – RN – 8400 Argentina

ABSTRACT

The fuel elements from nuclear research reactors consist in a laminated sandwich of aluminum with a core of some uranium compound. To process this material its necessary to previously eliminate the aluminum covering the fuel, before the conditioning of the rest of the fuel in a stable matrix, in order to obtain an acceptable waste form for a subsequent disposition in a geological repository. Normally, mechanical and chemical methods are proposed for that purpose.

In this work we focused our research in uranium silicide based fuels (20% enriched in U-235). We compare two methods for the conditioning of such fuel: in the first the aluminum is eliminated using solution of NaOH 5M, and in the second we keep some aluminum and treat it together with the uranium silicide core. The main difference is that one method is dry and respect to the other, eliminating the treatment of radioactive liquids, and avoiding a step which can cause some complication considering that all the process is going to be done in a “hot cell”. But in the second process due the important quantity of aluminum the volume increase in a 50%.

The ceramization step consist in using a U₃O₈ (natural or depleted) powder to both, dilute and act as an immobilization matrix, for the pretreated spent fuel. In this way it is possible to reduce the U²³⁵ enrichment of the fuel and create an homogeneous material having structural integrity and good corrosion resistance provided by the sinterization of the U₃O₈. This method (patent pending) has the advantage of avoiding the need of a vitrification process in which the volume involved increase substantially.

The ceramized material can be treated, regarding its final disposition, in the same way as the proposed alternatives for spent fuels of nuclear power plants.

We compared the leaching resistance in deionized water of the ceramized bodies with sintered U₃O₈ and UO₂, with satisfactory results.

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