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Magnetic Materials: Novel Monitors of Long-Term Evolution of Engineered Barrier Systems

School of Geosciences, University of Edinburgh, Edinburgh EH9 3FE, UK
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Academic Editors: Rebecca Lunn, Simon Norris and Jesus Martinez-Frias
Geosciences 2016, 6(4), 54; https://doi.org/10.3390/geosciences6040054
Received: 30 August 2016 / Revised: 11 November 2016 / Accepted: 24 November 2016 / Published: 7 December 2016
Most safety cases for the deep geological disposal of radioactive waste are reliant on the swelling of bentonite in the engineered barrier system as it saturates with groundwater. Assurance of safety therefore requires effective monitoring of bentonite saturation. The time- and fluid-dependent corrosion of synthetic magnets embedded in bentonite is demonstrated here to provide a novel and passive means of monitoring saturation. Experiments have been conducted at 70 °C in which neo magnets, AlNiCo magnets, and ferrite magnets have been reacted with saline (NaCl, KCl, CaCl2) solutions and alkaline fluids (NaOH, KOH, Ca(OH)2 solutions; pH = 12) in the presence of bentonite. Nd-Fe-B magnets undergo extensive corrosion that results in a dramatic change from ferromagnetic to superparamagnetic behaviour concomitant with bentonite saturation. AlNiCo magnets in saline solutions show corrosion but only limited decreases in their magnetic intensities, and ferrite magnets are essentially unreactive on the experimental timescales, retaining their initial magnetic properties. For all magnets the impact of their corrosion on bentonite swelling is negligible; alteration of bentonite is essentially governed by the applied fluid composition. In principle, synthetic magnet arrays can, with further development, be designed and embedded in bentonite to monitor its fluid saturation without compromising the integrity of the engineered barrier system itself. View Full-Text
Keywords: geological disposal facility; engineered barrier system; bentonite; buffer; magnets; Nd-Fe-B; neo magnets; ferrite; AlNiCo geological disposal facility; engineered barrier system; bentonite; buffer; magnets; Nd-Fe-B; neo magnets; ferrite; AlNiCo
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Harley, S.L.; Rigonat, N.; Butler, I.B. Magnetic Materials: Novel Monitors of Long-Term Evolution of Engineered Barrier Systems. Geosciences 2016, 6, 54.

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