Das Pratik, Vats Bal Govind, Samui Pradeep, Rai Abhishek Kumar, Yadav Ashok Kumar, Shafeeq Muhammed, Kesari Swayam, Parida Suresh Chandra
Product Development Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400085, India.
Homi Bhabha National Institute (HBNI), Mumbai 400094, India.
ACS Omega. 2024 Aug 10;9(33):35873-35887. doi: 10.1021/acsomega.4c04809. eCollection 2024 Aug 20.
The structure and stability of charge-coupled lanthanide-substituted Ca(PO)F as a potential fluoride-bearing nuclear waste form for the back-end fuel cycle of Gen-IV molten salt reactor have been studied in detail. Here, calcium fluorapatite (CaFAp) as a model structure was taken for incorporation of trivalent lanthanides (Lns, La-Lu except Pm) in a charge-coupled fashion, i.e., 2Ca = Na + Ln. In these fluorapatite phases, Na is substituted exclusively at nine coordinated sites, Ca1, while Ln is preferentially substituted at seven coordinated sites, Ca2. These compositions are further characterized for the local structure by Fourier transform infrared (FTIR) and Raman spectroscopy. Thermal expansion was measured by high-temperature X-ray diffraction (XRD) and the instantaneous thermal expansion coefficient correlates well with the unsubstituted CaFAp. The heat capacities of these solids were measured by differential scanning calorimetry and drop calorimetry, whereas enthalpies of formation were obtained by high-temperature oxide melt solution calorimetry. The thermodynamic analysis demonstrated that lanthanides having ionic radii closure to Ca (Sm and Gd) imparted higher thermodynamic stability to the substituted CaFAp as compared to that of other Ln. According to structural and thermodynamic investigations, entropy-stabilized fluorapatite waste from NaPrNdSmEuGdTbDyHoCa(PO)F (WF-Ln) was successfully synthesized for the first time. Furthermore, electron beam irradiation studies probed by XRD, FTIR, Raman, and X-ray absorption (XAS) spectroscopy implied the radiation resistance nature of this substituted CaFAps up to 20 MGy.
作为第四代熔盐反应堆后端燃料循环中一种潜在的含氟核废料形式，电荷耦合镧系元素取代的Ca(PO)F的结构和稳定性已得到详细研究。在此，以氟磷酸钙（CaFAp）作为模型结构，以电荷耦合方式掺入三价镧系元素（Ln，La-Lu除Pm外），即2Ca = Na + Ln。在这些氟磷灰石相中，Na仅在九个配位位点Ca1处被取代，而Ln优先在七个配位位点Ca2处被取代。通过傅里叶变换红外（FTIR）和拉曼光谱对这些组成的局部结构进行了进一步表征。通过高温X射线衍射（XRD）测量热膨胀，瞬时热膨胀系数与未取代的CaFAp相关性良好。通过差示扫描量热法和滴定量热法测量了这些固体的热容量，而通过高温氧化物熔体溶液量热法获得了生成焓。热力学分析表明，与其他Ln相比，离子半径与Ca接近的镧系元素（Sm和Gd）赋予取代的CaFAp更高的热力学稳定性。根据结构和热力学研究，首次成功合成了NaPrNdSmEuGdTbDyHoCa(PO)F（WF-Ln）的熵稳定氟磷灰石废料。此外，通过XRD、FTIR、拉曼和X射线吸收（XAS）光谱进行的电子束辐照研究表明，这种取代的CaFAp在高达20 MGy的剂量下具有抗辐射性。
