Radiolyse des systèmes eau-argile. Application au stockage des déchets radioactifs

¹ Laboratoire de chimie physique, université René-Descartes, URA 400, 45, rue des Saints-Pères, 75270 Paris Cedex 06, France.
² DCC/DSD/SCS, BP n° 6, 92265 Fontenay-aux-Roses, France.

Résumé

Nous étudions les modifications induites par le rayonnement ionisant sur l'argile Fo-Ca 7 et les eaux argileuses provenant du contact entre la roche et l'eau. L'irradiation provoque plusieurs changements dans le comportement du solide vis- à-vis de l'eau (solubilité des cations, pH d'équilibre, pouvoir réducteur). L'eau argileuse contient des capteurs de radicaux OH. En conséquence, le rendement de formation de l'eau oxygénée est plus élevé. Un schéma cinétique permettant de reproduire l’évolution de solutions d'eau oxygénée dans l'eau argileuse est proposé.

Abstract

The long-term storage of radioactive waste buried in deep geological formations raises numerous problems due to the radiolysis of the ground. In order to evaluate the consequences of the radiolytic reactions which will take place in the ground, we are studying the effect of y irradiation on the clay Fo-Ca 7 and on the clay water.

Concerning irradiation of the solid phase, the lixiviation of Fe2+ in acidic water increases with the dose, probably as a consequence of structural modifications. The non-irradiated clay water has reducing properties which are diminished upon irradiation. Clay water contains several unidentified efficient OH scavengers. As a consequence, the yield of hydrogen peroxide is higher in clay water than in pure water. The mechanism of H₂O₂ formation and decay has been studied in clay water and a kinetic scheme is proposed which allows the computation of the H₂O₂ amont for doses up to ca. 20,000 Gy. The efficient scavenging of OH free radicals is also consistent with a massive radiolytic formation of dihydrogen.