Lionel Campayo

Immobilization of radioactive iodine in silver aluminophosphate glasses.

Silver aluminophosphate glasses have been investigated as matrices for the immobilization of radioactive iodine. In this study, up to 28mol% AgI have been incorporated without volatilization thanks to a low temperature synthesis protocol. Alumina was added in the composition in order to increase the glass transition temperature for a better thermal stability in a repository conditions. Two series of glasses have been investigated, based on AgPO3 and Ag5P3O10 compositions, and with 0-5mol% Al2O3. We report (31)P, (27)Al and (109)Ag NMR study of these glasses, including advanced measurement of the connectivities through {(27)Al}-(31)P cross-polarization and (31)P-(31)P double-quantum correlation. We confirm that AgI is inserted in the aluminophosphate glasses and does not form clusters. AgI does not induce any modification of the glass polymerization but only an expansion of the network. Despite no evidence for crystallization could be obtained from XRD, NMR revealed that the introduction of AgI induces an exclusion of alumina from the network, leading to the crystallization of aluminophosphate phases such as Al(PO3)3 or AlPO4. As a consequence, despite NMR gives evidence for the presence of aluminophosphate bonds, only a limited effect of alumina addition on thermal properties is observed.

Incorporation of iodates into hydroxyapatites: a new approach for the confinement of radioactive iodine

A new strategy for the confinement of iodine has been developed: it consists in incorporating iodate anions (IO3−) into hydroxyapatite (Ca10(PO4)6(OH)2, HA). The iodate-substituted HA was synthesized by precipitation, and characterized in detail. Its thermal stability and resistance to leaching were then evaluated, revealing promising properties in view of radioactive iodine confinement applications.

Immobilization of iodine into a hydroxyapatite structure prepared by cementation

In order to manage radioactive iodine-129 coming from nuclear spent fuel, robust host matrices with durable long term behaviour need to be developed. In this work, a new process of synthesis of an iodate-substituted hydroxyapatite by means of a cementation route is described. This material was obtained from a mixture of tetracalcium phosphate (TTCP), tricalcium phosphate (αTCP) and sodium iodate (NaIO3), taken in a molar ratio of 1/2/0.5. The progress of the reaction leading to the setting and hardening of cement paste was monitored by combined measurements of electrical conductivity and heat flux release, together with XRD characterization of materials at definite times of hydration. Sodium iodate acts as a set retarder, by leading to the precipitation of non-cohesive transient phases, which are then destabilized when the massive precipitation of hydroxyapatite occurs. These delays can however be limited by adding hydroxyapatite seeds to the cement paste, which means that it is possible to control the setting time in view of an industrial application. This novel cementitious system leads to a porous material composed of iodine-substituted hydroxyapatite needles covering residual TTCP and αTCP particles. Iodine has entered the hydroxyapatite structure in the form of iodate anions only. An iodine incorporation rate of 6.5 wt% has been obtained by this cementitious system, which is a promising value in view of using these materials for the conditioning of radioactive iodine.