# Measurements of geopolymers conductivity as binder for encapsulation of metallic nuclear waste by impedance spectroscopy

Julia Agullo, Benoist Muzeau, Christian Bataillon

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Julia Agullo, Benoist Muzeau, Christian Bataillon. Measurements of geopolymers conductivity as binder for encapsulation of metallic nuclear waste by impedance spectroscopy. 11th Electrochemical Methods in Corrosion Research - EMCR 2015, 2015, Troia, Portugal. hal-04601420

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https://hal.science/hal-04601420v1

Submitted on 11 Oct 2024

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# Measurements of geopolymers conductivity as binder for encapsulation of metallic nuclear waste by impedance spectroscopy

Julia AGULLO<sup>a*</sup>, Benoist MUZEAU<sup>b</sup>, Christian BATAILLON<sup>c</sup>

<sup>a</sup> CEA, DEN, DANS, DPC, SCCME, Laboratoire d'Etude de la Corrosion Aqueuse, F-91191 Gif-sur-Yvette (France), tel +33 (0)1 69 08 50 20, fax +33 (0)1 69 08 15 86, julia.agullo@cea.fr

<sup>b</sup> CEA, DEN, DANS, DPC, SECR, Laboratoire d'Etude du Comportement des Bétons et des Argiles, F-91191 Gif-sur-Yvette (France), tel +33 (0)1 69 08 83 67, fax +33 (0)1 69 08 84 41, benoist.muzeau@cea.fr

<sup>c</sup> CEA, DEN, DANS, DPC, SCCME, Laboratoire d'Etude de la Corrosion Aqueuse, F-91191 Gif-sur-Yvette (France), tel +33 (0)1 69 08 15 91, fax +33 (0)1 69 08 15 86, christian.bataillon@cea.fr

The reprocessing of spent fuels from the French UNGG-Graphite Gas Natural Uranium-nuclear power plants, operated from the sixties until the 80'th in France, has generated cladding wastes such as Mg alloys. These wastes have been stored on site in Marcoule, until a definitive conditioning route is defined for the acceptance in the future geological disposal site. The CEA conditioning strategy is to encapsulate these Mg-wastes into a cement matrix, to produce a concrete waste package with an external metallic container. The main issue is hydrogen evolution as the consequence of the galvanic magnesium alloys corrosion. Geopolymer matrixes have been proposed as new binders for safe radioactive waste containment.

The purpose of this work was to investigate the conductivity of metakaolin-based geopolymer which could be used as mineral binder for encapsulation of metallic nuclear wastes. The formulation of this geopolymers includes NaF as corrosion inhibitor for Mg alloy wastes. Conductivity of the electrolyte is a key parameter of the galvanic corrosion. Electrochemical impedance spectroscopy (EIS) was carried out to determine the conductivity of geopolymers at different time (during the hydration process) to follow its evolution.

Two electrodes designs have been investigated in order to determine geopolymers conductivity. A simple two-electrode cell operated in the 1 MHz and 0.1 Hz frequency ranges gives a response typical for a porous electrode. These impedance diagrams are compared with the ones for an embedded dielectric sensor. This comparison shows that the cell geometry and electrode arrangement play an important role in the form of the frequency response. The evolution of Nyquist diagrams with time indicates an evolution of the pore geometry distribution in geopolymers.

**Keywords:** geopolymers, EIS, conductivity