Sarrasin L, Gaillard C, Panetier C, Pipon Y, Moncoffre N, Mangin D, Ducher R, Dubourg R
Institut Jean Lamour, UMR 7198 CNRS , Université de Lorraine , Campus Artem, 2 allée André Guinier , Nancy CEDEX 54011 , France.
Institut de Radioprotection et de Sureté Nucléaire , B. P. 3, St. Paul Lez-Durance CEDEX 13115 , France.
Inorg Chem. 2019 Apr 15;58(8):4761-4773. doi: 10.1021/acs.inorgchem.8b03076. Epub 2019 Mar 26.
Molybdenum is an abundant element produced by fission in the nuclear fuel UO in a pressurized water reactor. Although its radiotoxicity is low, this element has a key role on the fuel oxidation and other fission products migration, in particular in the case of an accidental scenario. This study aims to characterize the behavior of molybdenum in uranium dioxide as a function of environmental conditions (oxygen partial pressure, high temperature, UO oxidation) typical of an accidental scenario. To do so, molybdenum was introduced in UO or UO pellets by ion implantation, a technique that allows us to mimic the production of Mo in the nuclear fuel by fission. Then, thermal treatments at high temperature and different oxygen partial pressures were carried out. The mobility of Mo in UO samples was followed by secondary ion mass spectrometry (SIMS), while the Mo chemical speciation was investigated by spectroscopic techniques (XANES, Raman). In parallel, ab initio calculations were performed showing the effect of interstitial oxygen atoms on the Mo incorporation sites in UO. We show that the Mo mobility is directly connected to its chemical state, which in turn, is linked to the redox conditions. Indeed, under reducing atmosphere, Mo is present in UO or UO samples under a metallic state Mo(0). Its mobility, being quite low, is driven by a diffusion mechanism. An increase of pO entails the UO and Mo oxidation and, as a consequence, a strong release of this element. We show an increase of the Mo release rate with the increase of the UO hyper-stoichiometry x. After thermal treatment, Mo remaining in the samples is located in the grains under the MoO form. Our experimental results are assessed by ab initio calculations showing that in the presence of oxygen Mo atoms adopt in UO a local structure close to the octahedral local geometry of Mo oxides.
钼是压水反应堆中核燃料二氧化铀裂变产生的一种丰富元素。尽管其放射性毒性较低，但该元素在燃料氧化和其他裂变产物迁移方面起着关键作用，尤其是在事故情况下。本研究旨在表征二氧化铀中钼的行为与事故情况下典型环境条件（氧分压、高温、二氧化铀氧化）的关系。为此，通过离子注入将钼引入二氧化铀或二氧化铀颗粒中，该技术使我们能够模拟核燃料中钼通过裂变的产生过程。然后，在高温和不同氧分压下进行热处理。通过二次离子质谱（SIMS）跟踪钼在二氧化铀样品中的迁移率，同时通过光谱技术（XANES、拉曼）研究钼的化学形态。与此同时，进行了从头算计算，显示了间隙氧原子对钼在二氧化铀中掺入位置的影响。我们表明，钼的迁移率与其化学状态直接相关，而化学状态又与氧化还原条件有关。实际上，在还原气氛下，钼以金属态Mo(0)存在于二氧化铀或二氧化铀样品中。其迁移率相当低，由扩散机制驱动。氧分压的增加会导致二氧化铀和钼的氧化，结果是该元素的大量释放。我们表明，钼的释放速率随着二氧化铀超化学计量比x的增加而增加。热处理后，样品中残留的钼以MoO形式存在于晶粒中。我们的实验结果通过从头算计算进行评估，结果表明在有氧存在的情况下，钼原子在二氧化铀中采用的局部结构接近钼氧化物的八面体局部几何结构。
