Plutonium and Americium Aluminate Perovskites

Abstract

Both AmAlO3 and PuAlO3 perovskites have been synthesized and characterized using powder X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectroscopy (FT-IR), and 27Al magic angle spinning nuclear magnetic resonance spectroscopy (MAS NMR). AmAlO3 perovskite showed a rhombohedral configuration (space group R3̅c) in agreement with previous studies. The effect of americium α-decay on this material has been followed by XRD and 27Al MAS NMR analyses. In a first step, a progressive increase in the level of disorder in the crystalline phase was detected, associated with a significant crystallographic swelling of the material. In a second step, the crystalline AmAlO3 perovskite was progressively converted into amorphous AmAlO3, with a total amorphization occurring after 8 months and 2 × 1018 α-decays/g. For the first time, PuAlO3 perovskite was synthesized with an orthorhombic configuration (space group Imma), showing an interesting parallel to CeAlO3 and PrAlO3 lanthanide analogues. High-temperature XRD was performed and showed a Imma → R3̅c phase transition occurring between 473 and 573 K. The thermal behavior of R3̅c PuAlO3 was followed from 573 to 1273 K, and extrapolation of the data suggests that cubic plutonium perovskite should become stable at around 1850 K (R3̅c → Pm3̅m transition).

Synthesis, Characterization, and Stability of Two Americium Vanadates, AmVO3 and AmVO4

“…The requirements for a stable solid form are very diverse, ranging from storage on earth and operation in space to safe performance in case of accidents and post-accident scenarios. Our group studied several ceramic forms containing significant specific Am amounts, − the present study being in line with the past efforts.…”

“…Moreover, 237 Np (the decay product of 241 Am) tends to segregate as a fluorite fcc secondary phase, creating interfaces and inducing stress in the material. Comparing the existing data on Am-containing ceramics with fluorite, pyrochlore, zircon, monazite, and perovskite structures, the (Am,U)­O 2 , fluorite solid solution seems currently to be the most suitable form for space applications.…”

Synthesis, Characterization, and Stability of Americium Phosphate, AmPO4

“…As expected in the case of radiation damage induced defects, signal broadening takes place, and additionally the overlapping of all the peaks. 7,43 Due to these spectral changes, it was not possible to obtain a quantitative spectrum and differentiate neatly the crystalline from the amorphous phase. Nonetheless, we noticed that the feature previously attributed to peak 1 (mostly P(OAm) 7 species) was still present with a 31 P NMR shift almost similar to the fresh sample (300 ± 5 ppm vs. 282 ppm) while its line broadening was increasing over time (Figure 5d).…”

“…This is the reason why we started to look for alternative stable forms of americium compounds with high americium density as potential space power source materials. Thus, we have focused our effort on the synthesis and characterization of Am-containing compounds with light elements, such as AmAlO 3 7 (76% Am) and AmPO 4 (72% Am). Actinide phosphates are well-known for their stability, being proposed as ceramic nuclear waste forms.…”

New sample stage for characterizing radioactive materials by X-ray powder diffraction: application on five actinide dioxides ThO2, UO2, NpO2, PuO2 and AmO2

“…238 Pu and 241 Am) and the associated disintegrations are known to generate a broadening in the XRD peaks due to the induced structural disorder (Clinard et al, 1982;Weber, 1983;Horlait et al, 2013). In some materials, the structural damage generated by decay can lead to a complete amorphization of the material (Walter et al, 2007;Vigier et al, 2019). Furthermore, the self-irradiation generally induces a significant lattice swelling over time (Turcotte, 1976;Weber, 1984;Baclet et al, 2007;Thiebaut et al, 2007;Ravat et al, 2007;Nishi et al, 2013;Lebreton et al, 2014, (Baena et al, 2015) 5.47127 ( 8) (Leinders et al, 2015) 5.434 (1) (Chollet et al, 2014(Chollet et al, , 2012 5.39819 (1) (Belin et al, 2004) 5.3755 ( 5) (Vauchy et al, 2017) 5.593 (3) (Horlait et al, 2012) 5.4702 (4) (Yamashita et al, 1997) 5.4338 (3) (Yamashita et al, 1997) 5.3954 (4) (Yamashita et al, 1997) 5.375 (1) (Epifano et al, 2017(Epifano et al, , 2016 5.5974 (6) (Yamashita et al, 1997) 5.470 (Markin & Street, 1967) 5.4328 (2) (Fahey et al, 1974) 5.3953 (4) (Noe & Fuger, 1974) 5.3733 (Fahey et al, 1974) 5.5972 (5) (Zachariasen, 1948) 5.4704 (1) (Baldock et al, 1966) 5.434 (Sudakov et al, 1973) 5.3960 (3) (Ellinger, 1961) 5.377 (3) (Zachariasen, 1949) Figure 12 Experimental lattice parameters of the fluor...…”