The accident at the Fukushima Daiichi nuclear power plant four years ago has drawn attention to the environmental impact that the release of fission products from nuclear fuels can have in the event ...of a severely damaged reactor core. Three such accidents have occurred in the history of civil nuclear power.
Kovacs et al explore quantum chemical calculations and experimental investigations of molecular actinide oxides. In their analysis, they focus on topics such as electron correlation, relativistic ...effects, electronic spectroscopy, infrared spectroscopy, ion-molecule reactions, and the ground-state electronic structure of actinide monoxides.
Faced with the prospect of building a new fleet of conventional but improved generation III (Gen III) nuclear reactors and the challenges of designing future Gen IV systems, the materials community ...is currently re-establishing its fascination with nuclear materials. Although worldwide research support remains patchy, a number of countries are, once again, focusing a greater proportion of their strategic funding on nuclear science and engineering projects.
TaC, HfC and their solid solutions are promising candidate materials for thermal protection structures in hypersonic vehicles because of their very high melting temperatures (>4000 K) among other ...properties. The melting temperatures of slightly hypostoichiometric TaC, HfC and three solid solution compositions (Ta
Hf
C, with x = 0.8, 0.5 and 0.2) have long been identified as the highest known. In the current research, they were reassessed, for the first time in the last fifty years, using a laser heating technique. They were found to melt in the range of 4041-4232 K, with HfC having the highest and TaC the lowest. Spectral radiance of the hot samples was measured in situ, showing that the optical emissivity of these compounds plays a fundamental role in their heat balance. Independently, the results show that the melting point for HfC
, (4232 ± 84) K, is the highest recorded for any compound studied until now.
UO2 samples doped with 6, 11, 22 mol% lanthanum were examined before and after air oxidation. To verify the formation of uranium–lanthanum‐mixed oxide solid solutions, powder X‐ray diffraction (XRD) ...analyses of the crystalline phases in the materials were carried out. The presence of oxygen vacancies in the La‐doped UO2 samples was identified by Raman spectrometry. It was evidenced by changes induced in the Raman spectra by air oxidation. This latter was carried out either by increasing the Raman laser power or by thermally treating the samples at 500 K for 370 h. In addition, oxidation behavior differences of pure and La‐doped UO2 samples were reported by comparing XRD and Raman results of the samples before and after air oxidation. It was shown that the concentration of the M4O9 (M: U, La) phase increased with increasing content of La, whereas inhibition for the formation of M3O8 phase was observed.
Americium 241 is a potential alternative to plutonium 238 as an energy source for missions into deep space or to the dark side of planetary bodies. In order to use the 241Am isotope for radioisotope ...thermoelectric generator or radioisotope heating unit (RHU) production, americium materials need to be developed. This study focuses on the stabilization of a cubic americium oxide phase using uranium as the dopant. After optimization of the material preparation, (Am0.80U0.12Np0.06Pu0.02)O1.8 has been successfully synthesized to prepare a 2.96 g pellet containing 2.13 g of 241Am for fabrication of a small scale RHU prototype. Compared to the use of pure americium oxide, the use of uranium-doped americium oxide leads to a number of improvements from a material properties and safety point of view, such as good behavior under sintering conditions or under alpha self-irradiation. The mixed oxide is a good host for neptunium (i.e., the 241Am daughter element), and it has improved safety against radioactive material dispersion in the case of accidental conditions.
► A thermodynamic modelling of the U-Pu-O-C system is derived using the CALPHAD method. ► The calculated phase diagrams of all the sub-systems and the thermodynamic properties of all the phases are ...described and found in good agreement with the experimental data. ► The variation of the oxygen potential in oxide fuels versus oxygen to metal ratio is explained by the change of the cation oxidation states and the formation of oxygen vacancies and interstitials.
In the present work a thermodynamic model is derived for the (U, Pu)O
2 oxide, the (U, Pu)C carbide fuels using the Calphad method to describe consistently both phase diagrams and thermodynamic data of the phases involved in the U–Pu–O–C system. All the available thermodynamic and phase diagram data of the binary and ternary sub-systems are very well reproduced by our model. For the quaternary system, the calculated phase equilibria in the U
0.3Pu
0.7–C–O region are in good agreement with the experimental data.
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).
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