Encrustation prevention of zirconium molybdate hydrate

Arai, Takahiro*; Ito, Daiyu*; Hirasawa, Izumi*; Miyazaki, Yasunori  ; Takeuchi, Masayuki 

In reprocessing process, spent nuclear fuel is dissolved by HNO. Mo and Zr in the acidic solution react to form zirconium molybdate hydrate (ZMH). ZMH adheres to the inner-surface of reprocessing equipment, giving a great influence on stable operation. Conventional anti-encrustation is achieved by cleaning the surface of the reprocessing equipment by high pressure water and dissolving wall deposits by acid or alkaline solution. However, the former increases radioactive waste volume, and the latter contributes to corrosion of the metal surface. In this study, encrustation mechanism of ZMH crystal was investigated based on the deposited mass on the solid surface. Observing the deposition process, it was clarified that ZMH fine crystal growth is accelerated and agglomerated, followed by the rapid deposition. Total deposited mass decreased not only by lowering initial ratio of Mo and Zr concentration under the range of 1.0 Mo/Zr 2.0, but also by lowering HNO concentration.