Annual Report 2009/2010 - JUWEL - Forschungszentrum Jülich

5.7.
Synthesis and thermal treatment of uranium-based
microspheres through internal gelation
H. Daniels, S. Neumeier, G. Modolo
Corresponding author: g.modolo@fz-juelich.de
Abstract
An alternative to the direct final disposal of long-lived radionuclides is their separation
(partitioning) from the original waste in connection with a subsequent appropriate treatment.
The general aim is to lower the risk potential coming along with the radioactivity
(radiotoxicity).
A promising concept after the partitioning step is the embedding of Am, Cm & Np, the “Minor
Actinides” (MA), in uranium-based nuclear fuel (co-conversion). Through this the MAs can be
eliminated by nuclear reactions with fast neutrons (transmutation) in upcoming reactor
concepts.
One way to obtain such fuel is the internal-gelation process: Amorphous gel-spheres are
created and thermally treated at comparably low temperatures to become crystalline. The
main advantages are the high automation potential as well as the co-conversion being
carried out predominantly in aqueous solutions without dust-creation.
The formulation of stable precursor solutions for the gelation is one crucial step towards a
reliably working process. Therefore MA-surrogates were utilised for basic research on
reaction mechanisms and speciation in the corresponding aqueous phases. Subsequently,
the UO 2 -based ceramics obtained through thermal treatment of the gels were characterised
to optimise the calcination and sintering process.
Introduction
Advanced nuclear fuel management with the help of new reactor generations needs
appropriate fuel matrices. A UO 2 based fuel with addition of minor actinides can serve as a
fuel and transmutation matrix in parallel. Fabrication of such fuels has high demands due to
radiotoxicity and contamination issues. A procedure minimising the connected risks is highly
beneficial.
Internal gelation is a well known method to produce microspheres suitable as sphere-pac
fuel or as precursors for fuel pellet fabrication. One variant of internal gelation was developed
in Forschungszentrum Jülich by Förthmann et al. [1] In contrast to KEMA- and similar
processes [2], the gelating agents were added in solid form. The advantage of this variant is
the resulting higher effective uranium concentration in the precursor solution due to a less
overall volume of water needed for solvation of the chemicals. Therefore, the preparation of
acid deficient uranyl nitrate (ADUN), which leads to a higher uranyl solubility, is nonessential
[1].
The work in 2010 focused on the investigation of chemical interactions between the involved
species in solution and the thermal treatment of obtained uranium / neodymium
microspheres through internal gelation. For the experiments, neodymium was utilized as a
surrogate for a trivalent actinide such as americium. Additionally, creation ADUN through
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