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@INPROCEEDINGS{Schreinemachers:893763,
      author       = {Schreinemachers, Christian and Bollen, Olivier and
                      Leinders, Gregory and Tyrpekl, Václav and Modolo, Giuseppe
                      and Verwerft, Marc and Binnemans, Koen and Cardinaels,
                      Thomas},
      title        = {{H}ydrolysis of uranium({VI}), neodymium({III}) and
                      cerium({III}/{IV}) by thermal decomposition of urea},
      reportid     = {FZJ-2021-02818},
      year         = {2021},
      abstract     = {<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>},
      month         = {Jun},
      date          = {2021-06-29},
      organization  = {Uranium Science 2021, virtual event
                       (UK), 29 Jun 2021 - 1 Jul 2021},
      subtyp        = {Other},
      keywords     = {uranium (Other) / neodymium (Other) / cerium (Other) /
                      ammonium diuranate (Other) / ADU (Other) / Nuclear fuel
                      fabrication (Other) / Co-conversion (Other) / GenIV (Other)
                      / pH (Other) / XRD (Other) / SEM (Other)},
      cin          = {IEK-6},
      cid          = {I:(DE-Juel1)IEK-6-20101013},
      pnm          = {1411 - Nuclear Waste Disposal (POF4-141) / GENIORS - GEN IV
                      Integrated Oxide fuels recycling strategies (755171)},
      pid          = {G:(DE-HGF)POF4-1411 / G:(EU-Grant)755171},
      typ          = {PUB:(DE-HGF)6},
      doi          = {10.5281/ZENODO.5034714},
      url          = {https://juser.fz-juelich.de/record/893763},
}