Acoustic Cavitation near Metal Surfaces Contaminated with Radionuclides
Résumé
In the nuclear field, decontamination of radioactive metal surfaces under power ultrasoundprovides an interesting possibility for the decommissioning of retired or disabled nuclearinstallations and reducing the radioactive solid waste volume. This method uses thephenomenon of acoustic cavitation resulting from the propagation of an ultrasonic wave in aliquid medium. Microbubbles are formed, then grow, oscillate and finally collapse violently,which leads to the emergence of violent shock waves and micro-jets directed towards thesolid surface, in combination to the in-situ generation of chemically active species.This investigation has two main study domainsi) Sonoluminescence approachTo better understand the mechanisms of acoustic cavitation at the metal / solutioninterface, 362 kHz power ultrasound is applied to 1 M NaCl solution under Ar gas flow.The metal surface position induces variation on the sonoluminescence intensity of activeradicals (OHet729; and Naet729;), which proves the effect of a solid surface on cavitation bubbles'deformation within short range (et8776; 3 mm).ii) Ultrasonic decontamination mechanism studyTo optimize the experimental conditions (ultrasonic frequency, the saturating gas, thecomposition of the solution, temperature, etc.), the surfaces toughness and morphologyevolution of Mg surfaces are followed by SEM and contact angle during the treatment ofagitation and sonication under 205 kHz within 10-3 M oxalic acid. Mg surface is quicklytransformed from hydrophobic to hydrophilic due to the acid corrosion. And aftersonication, pits with golf ball dimple shape surface occur and a secondary phase appears.
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