Electrochemical immobilization of Cs in single-crystalline SYNROC

The development of a disposal technique for the radiotoxic 137Cs in nuclear wastes is one of the most urgent issues in nuclear fuel technology. An effective disposal method of 137Cs is to immobilize it in a synthetic rock (SYNROC) material: cesium titanate hollandite, 137CsxTi8O16 (I4/m, image, image). Practical applications of 137CsxTi8O16 have been restricted so far because the conventional synthetic method requires strong chemical reducers and reaction temperatures higher than 1250 °C. In this report, we present a milder preparation method of CsxTi8O16 by electrolysis of a mixture of Cs2MoO4 and TiO2 in ambient atmosphere at 900 °C. The Cs content in the resultant single-crystalline Cs1.35Ti8O16 is competitive with the highest value in polycrystalline Cs1.36±0.03Ti8O16 prepared by the conventional synthetic method. The electrochemical preparation of Cs1.35Ti8O16 is a promising way to immobilize a high quantity of 137Cs ions in a stable form of single-crystalline SYNROC.