Purified uranyl nitrate (UO2(NO3)2) solutions from the final purification cycle are concentrated by evaporation in order to obtain solutions of 300-400 g U/l, which can be reused or stored (Fig. 16.14).

‘ Less dense

phase outlet

Separating zone

И More dense

Vі phase inlet

Clean-in-place nozzles

Operating centrifugal contactor stage

16.13

Left: Cutaway view of an operating centrifugal extractor (Jack D. Law and Terry A. Todd, Idaho National Laboratory) Right: Schematics of a centrifugal extractor (F. Drain, R. Vinoche, J. Duhamet, WM’03 Conference, February 23-27, 2003, Tucson, AZ).

Plutonium nitrate is converted into PuO2 at the end of the purification cycle to avoid storage and transportation of solutions (Fig. 16.15).

The plutonium at valence IV is precipitated by oxalic acid into plutonium oxalate:

Pu4+ + 2 H2C2O4 + xH2O ^ Pu (C2O4)2. xH2O + 4 H+

The precipitate is washed, dried and calcined into oxide at 400 °C: Pu (C2O4)2. xH2O ^ PuO2 + xH20 + 2CO + 2CO2 The whole PUREX process is shown in Fig. 16.16.

I From Pu nitrate purification |