Session: 05-05: Vitrification Process Developments

Paper Number: 110227

110227 - Nuclear Waste Treatment: Vitrification of Iron-Phosphate Sludge 

Within the framework of developing advanced processes for nuclear waste treatment, Ansaldo Nucleare has studied and tested an innovative technology to perform the conditioning of radioactive ferrous waste material, Low and Intermediate Level Waste (LILW), resulting from decommission activities of Nuclear Facilities.

This technology is based on a patent process dedicated to the treatment, and recirculation, of decontamination solutions coming from the pickling process of the metal waste, with the aim to obtain an inert final product. The process results in the production of a radioactive sludge, made mostly of iron-phosphate salts, which can be thermally treated to produce a ready-to-storage, homogenous and chemically resistant glass product.

Laboratory research demonstrated that the obtained material does not require any additional conditioning treatment, resulting in a decreased volume footprint of the final waste compared with alternative and more consolidated methods (e.g. grouting conditioning system).

Lab-scale Research programs, carried out in collaboration with Stazione Sperimentale del Vetro in Murano (SSV), demonstrated that iron phosphate sludges can be molten at temperatures around 1150°C yielding a glass material with excellent chemical resistance properties.

Moreover, it was demonstrated that the addition of small amounts of “fluxing” chemicals reduces the melting temperature of the iron phosphate, down to ~ 1025°C, thus benefiting the retention yields and easing the vitrification process. Milder conditions are desired to reduce the furnace’s environmental impact, as well as allowing its operation and design under safer conditions.

Given the results coming from the laboratory scale testing, other experiments were carried out on a pilot plant. The intermediate-scale plant was designed and built with the support of industrial partners and suppliers.

The sludges and glass products coming from the pilot plant were characterized with ICP-MS, XRF, XRD and leaching analyses.

Specific tests with iron phosphates sludges doped with small amounts (≈5000 ppm, max) of radionuclide simulants such as Cs, Ni, Sr and Co demonstrated that their retention yields are larger than 95%, and only a fraction of the P₂O₅ is lost during the melting process.

The main strengths of this innovative technology are:

-    Lower costs associated with the nuclear waste storage;

-    Lower materials requested for the waste treatment;

-    Facility with reduced footprint;

-    Long-term stability of the waste.

During the test period that was performed at the pilot plant, some technological and scientific challenges have been encountered. To better understand the mechanism behind the vitrification and to properly manage all the variables that come into play in the process, additional experimental tests will be planned accordingly.

Presenting Author: Francesca Valente Ansaldo Nucleare S.p.A.

Presenting Author Biography: Francesca Valente,
graduated in Chemical Sciences in 2021 from the University of Genoa. She has been working in Ansaldo Nucleare for almost 2 years.
During her experience in Ansaldo, she had the chance to follow different projects on the radwaste management, especially on vitrification procedures. Along with her team, she collaborated with Politecnico di Milano, to research the mechanism behind acid decontamination and vitrification.