TY  - CONF
AU  - Schreinemachers, Christian
AU  - Bollen, Olivier
AU  - Leinders, Gregory
AU  - Tyrpekl, Václav
AU  - Modolo, Giuseppe
AU  - Verwerft, Marc
AU  - Binnemans, Koen
AU  - Cardinaels, Thomas
TI  - Hydrolysis of uranium(VI), neodymium(III) and cerium(III/IV) by thermal decomposition of urea
M1  - FZJ-2021-02818
PY  - 2021
AB  - <p><strong>Abstract</strong></p> <p>Uranium dioxide is used as conventional fuel for the production of energy by nuclear fission.&nbsp;Even though the front-end of the nuclear fuel cycle is well known, studies to investigate alternative&nbsp;fabrication routes to prepare precursors for oxidic uranium-based fuels are ongoing. The precipitation induced by thermal decomposition of urea has been demonstrated for several metals (e.g.&nbsp;Ti, Ni, Cu, Zn, Ce, Th), and a modified hydrothermal approach has been applied to precipitate&nbsp;ammonium diuranate (ADU) from a solution containing uranyl ions.</p> <p>Within this study, we investigated the hydrolysis behaviour of uranyl and lanthanide mixtures&nbsp;to support the development of&nbsp; alternative fabrication routes for transmutation fuel, such as sol-gel processes. The lanthanides Nd and Ce acted as surrogates for the actinides Am and Pu,&nbsp;respectively. We specifically sought out parameters for the hydrolysis of uranyl ions induced by&nbsp;thermal decomposition of urea at ambient pressure. Moreover, the hydrolysis behaviour of Nd(III),&nbsp;Ce(III) and Ce(IV), as well as mixtures of the lanthanide- and uranyl ions, was investigated using&nbsp;the conditions determined for uranyl. Hydrolysis experiments were carried out at 90 &deg;C and 100 &deg;C&nbsp;for <em>n</em>(urea) :&nbsp;<em>n</em>(UO<sub>2</sub><sup>2+</sup>) ratios of 26&nbsp;and 52. The solution was sampled during the precipitation&nbsp;reaction to monitor its pH and certain samples were analysed applying UV/VIS spectroscopy&nbsp;and inductively coupled plasma mass spectrometry, while powder X-ray diffraction and scanning&nbsp;electron microscopy were applied to characterise the precipitates.</p> <p>Uranyl ions hydrolysed between pH 5.1 and pH 5.5 and the experimental conditions impacted&nbsp;the reaction kinetics significantly. A temperature increase from 90 &deg;C to 100 &deg;C reduced the time to&nbsp;finish the precipitation by about 66 %, whereas a doubling of the urea content decreased the reaction&nbsp;time by about 33 %. ADU precipitates of different composition (<em>x</em> UO<sub>3</sub> &middot; <em>y</em> NH<sub>3</sub> &middot; <em>z</em> H<sub>2</sub>O) formed&nbsp;under the applied conditions. For trivalent Nd and Ce, a comparable pH evolution and lanthanide&nbsp;carbonate hydroxide (<em>Ln</em>CO<sub>3</sub>OH) products were observed, whereas tetravalent Ce hydrolysed at a&nbsp;lower pH forming CeO<sub>2</sub>. The precipitation behaviour was confirmed for solutions containing binary&nbsp;mixtures of uranyl and lanthanide cations, while a simultaneous precipitation of Nd(III) and Ce(III)<br> was observed for ternary U/Nd/Ce compositions. For the latter, a partial incorporation of the <em>Ln&nbsp;</em>phase into the ADU phase was observed, whereas the precipitation in the presence of Ce(IV)/CeO<sub>2</sub>&nbsp;led to the formation of three separate phases. In this contribution we will report and discuss the&nbsp;experimental results.</p>
T2  - Uranium Science 2021
CY  - 29 Jun 2021 - 1 Jul 2021, virtual event (UK)
Y2  - 29 Jun 2021 - 1 Jul 2021
M2  - virtual event, UK
KW  - uranium (Other)
KW  - neodymium (Other)
KW  - cerium (Other)
KW  - ammonium diuranate (Other)
KW  - ADU (Other)
KW  - Nuclear fuel fabrication (Other)
KW  - Co-conversion (Other)
KW  - GenIV (Other)
KW  - pH (Other)
KW  - XRD (Other)
KW  - SEM (Other)
LB  - PUB:(DE-HGF)6
DO  - DOI:10.5281/ZENODO.5034714
UR  - https://juser.fz-juelich.de/record/893763
ER  -