Immobilisation of nuclear waste materials containing different alkali elements into single-phase NZP-based ceramics

A single-phase host matrix based upon the sodium zirconium phosphate (NZP) structure and designed to immobilise commercial nuclear waste was investigated. In comparison with other waste forms the important advantage of the NZP ceramics is its ability to incorporate, at crystallographic levels, alkali elements without significant deterioration of the physical and chemical matrix stability. Studies on the incorporation of different alkali elements into the NZP host structure were performed. Single-phase phosphates corresponding to crystalline solutions (continuous and limited) with a structure similar to NZP were found in the series of compounds with the general formula A1-x+4yA'xE2-y(PO4)3 (y = 0, 0.5 and 1, and 0 ≤ x ≤ 1+4y), where A-A' are different alkali elements (Li, Na, K, Rb, and Cs) and E are Ti or Zr. Leaching studies with alkali containing samples revealed reasonable resistance towards the release of the constituents. (author)