Feuchter Hervé, Duval Sylvain, Volkringer Christophe, Ouf François-Xavier, Rigollet Laurence, Cantrel Laurent, De Mendonca Andrade Matheus, Salm François, Lavalette Claire, Loiseau Thierry
Université de Lille, CNRS, Centrale Lille, ENSCL, Univ. Artois, UMR 8181-UCCS-Unité de Catalyse et Chimie du Solide, F-59000 Lille, France.
Institut Universitaire de France (IUF), 1, rue Descartes, 75231 Paris cedex 05, France.
ACS Omega. 2019 Jul 31;4(7):12896-12904. doi: 10.1021/acsomega.9b00746.
Modeling of plutonium(IV) behavior during an accidental fire in a reprocessing plant was considered using various non-radioactive metallic surrogates. Among those elements, cerium(IV) was supposed to be a suitable candidate due to possible formation of a complex with TPB, but its extractability and stability have not been studied previously under representative plutonium uranium reduction extraction (PUREX) conditions. In this work, we investigated the chemical analogy between cerium(IV) and plutonium(IV) in this extractive process and combustion thereof. Distribution ratios are reported for acidities of 1-4 mol L in equal volumes of nitric acid and a 30:70 mixture of tributylphosphate and hydrogenated tetrapropylene. The influences of light, temperature, and extraction time were studied by UV-vis spectroscopy. The results showed that cerium(IV) is extracted quantitatively but is reduced over time to cerium(III) in the organic mixture. Spectrophotometric investigations of this reaction kinetics revealed an apparent rate constant of 0.021 ± 0.002 mol L min at 298 K and an apparent fractional reaction order of 0.5. The activation energy of this reduction was found to be around 82 ± 2 kJ mol by the Arrhenius plot method. The combustion of mono- and biphasic solutions prepared with a cerium(IV) concentration of 10 g L revealed that the extracted complexes, CeO·6NO·3TBP or CeO·8NO·6TBP, are reduced during the combustion. Compositions of the resulting ashes and soot were analyzed and highlighted the presence of pyrophosphates and polycyclic aromatic hydrocarbons, with some traces of cerium. Ce(IV) is not suitable to represent Pu(IV) from a chemical point of view in HNO/TBP-HTP solutions.
利用各种非放射性金属替代物对后处理厂意外火灾期间钚（IV）的行为进行了建模。在这些元素中，铈（IV）被认为是一个合适的候选者，因为它可能与磷酸三丁酯形成络合物，但其萃取率和稳定性此前尚未在具有代表性的钚铀还原萃取（PUREX）条件下进行研究。在这项工作中，我们研究了铈（IV）和钚（IV）在该萃取过程及其燃烧过程中的化学相似性。报道了在等体积硝酸以及磷酸三丁酯与氢化四丙烯30:70混合物中，酸度为1 - 4 mol/L时的分配比。通过紫外 - 可见光谱研究了光照、温度和萃取时间的影响。结果表明，铈（IV）被定量萃取，但在有机混合物中会随着时间被还原为铈（III）。对该反应动力学的分光光度研究表明，在298 K时表观速率常数为0.021 ± 0.002 mol/(L·min)，表观分数反应级数为0.5。通过阿累尼乌斯作图法发现该还原反应的活化能约为82 ± 2 kJ/mol。对浓度为10 g/L的铈（IV）制备的单相和双相溶液的燃烧研究表明，萃取的络合物CeO·6NO·3TBP或CeO·8NO·6TBP在燃烧过程中被还原。对所得灰烬和烟灰的成分进行了分析，突出了焦磷酸盐和多环芳烃的存在，还有一些铈的痕迹。从化学角度来看，在HNO/TBP - HTP溶液中，Ce(IV)不适合代表Pu(IV)。
