Hydrolysis of Uranyl‐, Nd‐, Ce‐Ions and their Mixtures by Thermal Decomposition of Urea

Christian Schreinemachers,Koen Binnemans,Olivier Bollen,Gregory Leinders,Marc Verwerft,Giuseppe Modolo,Václav Tyrpekl,Thomas Cardinaels

doi:10.1002/ejic.202100453

Abstract

AbstractThe hydrolysis of uranyl‐, Nd‐ and Ce‐cations, induced by thermal decomposition of urea was investigated and the impact of the urea content and the experiment temperature on the reaction kinetics was evaluated. Uranyl precipitated as ammonium diuranate (ADU) with varying stoichiometry. Nd(III) and Ce(III) showed comparable pH evolutions and lanthanide carbonate hydroxide (LnCO3OH) products were identified, whereas Ce(IV) hydrolysed at lower pH and formed CeO2. The precipitation behaviour was confirmed for mixtures of uranyl and the lanthanides. Depending on the urea content, a partial co‐precipitation occurred in U/Nd mixtures. The phases formed with Ce(III) and Ce(IV) were also identified in the precipitates of binary U/Ce mixtures. In ternary U/Nd/Ce compositions, a simultaneous precipitation of Nd(III) and Ce(III) was observed and a partial incorporation of the lanthanides into the ADU phase, whereas the precipitation in the presence of Ce(IV)/CeO2 led to the formation of three individual phases.

Highlights

Partitioning and transmutation is a key strategy to reduce spent nuclear fuels’ radiotoxicity and heat generation.[1]
The conditions applied during the hydrolysis experiments were adopted from Wangle et al.,[12] who investigated the homogeneous hydrolysis of thorium by thermal decomposition of urea at 90 °C and 100 °C using molar amounts of urea corresponding to 5, 25 and 50 times the molar Th content (c(Th) = 0.05 mol LÀ 1)
The hydrolysis reactions were followed-up by pH measurements, ultraviolet-visible spectroscopy (UV/Vis), and inductive coupled plasma mass spectrometry (ICP-MS) and the precipitates were characterised by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM)

Summary

Introduction

Partitioning and transmutation is a key strategy to reduce spent nuclear fuels’ radiotoxicity and heat generation.[1] Long-lived minor actinides (MAs) are partitioned from spent nuclear fuel and subsequently converted into precursors to manufacture fuel pins or target materials. These types of nuclear fuels can be used in fast reactor systems to fission the MAs into short-lived radioisotopes. An essential link between the partitioning and the transmutation is the conversion of the separated MAs into solid precursors to fabricate fresh fuel suitable for MA recycling. In the sol-gel process a spherically shaped precipitate is formed and thermally converted into an oxide, which can directly be used as particle fuel[3] or compressed into the commonly used fuel pellets.[4]

Methods

Results

Discussion

Conclusion