Nucleation and crystal growth of zirconium molybdate hydrate in nitric acid

Abstract

Zirconium molybdate hydrate can precipitate in nitric acid media during the process of spent nuclear fuel recycling. The precipitates can occur either in the nitric acid dissolution solution or in the waste fission product solution, and can lead to the formation of fouling layers. If such layers are left to grow, they can generate dysfunctions requiring heavy mechanical intervention and lead to production losses. In order to reduce the fouling risk as much as possible, nucleation and crystal growth data of zirconium molybdate hydrate in nitric acid are used to propose a fouling mechanism. Two parameters, supersaturation ratio and temperature, are used with the classical theory of primary nucleation to describe the stability of the supersaturated solutions within an observation time scale of approximately one hour. A quartz crystal microbalance is used to measure zirconium molybdate hydrate crystal growth kinetics on an initial crystal deposit. The collected data allocated four zones delimited by supersaturation ratios and temperatures, each zone describing a specific behaviour of zirconium and molybdenum solutions in nitric acid. As a result, a fouling scenario is proposed and the data is used to greatly limit its growth.