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The thermal scattering laws (TSL) take into account the crystalline structure and atomic motions of isotopes bound in materials. This paper presents the CINEL code, which was developed to generate temperature-dependent TSL for solid, liquid and free gas materials of interest for nuclear reactors. CINEL is able to calculate TSL from the phonon density of states (PDOS) of materials under the Gaussian-Incoherent approximations. The PDOS can be obtained by using theoretical approaches (e.g., ab initio density functional theory and molecular dynamics) or experimental results. In this work, the PDOS presented in the ENDF/BVIII.0 and NJOY-NCrystal libraries were used for numerical validation purposes. The CINEL results are in good agreement with those reported in these databases, even in the specific cases of TSL with the newly mixed elastic format. The coding flexibility offered by Python using the JupyterLab interface allowed to investigate limits of physical models reported in the literature, such as a four-site model for UO2, anharmonic behaviors of oxygen atoms bound in a Fm3m structure, texture in Zry4 samples and jump corrections in a roto-translational diffusion model for liquid water. The use of graphic processing units (GPU) is a necessity to perform calculations in a few minutes. The performances of the CINEL code is illustrated with the results obtained on actinide oxides having a Fm3m structure (UO2, ThO2, NpO2 and PuO2), low enriched fuel (UMo), cladding (Zry4) and moderators (H2O with a specific emphasis on ice).

A large variety of materials contain both carbon and oxygen atoms, in particular oxidized carbides, carbon alloys (as ZrC, UC, steels, etc.), and oxycarbide compounds (SiCO glasses, TiCO, etc.). Here a new ion beam analysis methodology is described which enables quantification of elemental composition and oxygen concentration profile over a few microns. It is based on two procedures. The first, relative to the experimental configuration relies on a specific detection setup which is original in that it enables the separation of the carbon and oxygen NRA signals. The second concerns the data analysis procedure i.e. the method for deriving the elemental composition from the particle energy spectrum. It is a generic algorithm and is here successfully applied to characterize an oxidized uranium carbide sample, developed as a potential fuel for generation IV nuclear reactors. Furthermore, a micro-beam was used to simultaneously determine the local elemental composition and oxygen concentration profiles over the first microns below the sample surface. This method is adapted to the determination of the composition of MCOcompounds with a sensitivity on elemental atomic concentrations around 1000 ppm. [ABSTRACT FROM AUTHOR]

The implantation of He ions in UO2 polycrystals induces a strain in the implanted layer which can be characterized using Laue micro X-ray diffraction (µ-XRD). The strain tensor resulting from the ion implantation may not be reduced to a single out-of-plane strain component: it also has nonzero shear components. Their strong dependence upon crystal orientation is modeled using elasticity theory. This work demonstrates the potential of Laue µ-XRD for characterizing radiation effects in materials. [ABSTRACT FROM AUTHOR]

Raman measurements were carried out to probe the spectroscopic signatures of the ion beam irradiation-induced damage and their in-depth profiles on a Uranium dioxide sample previously cut and polished prior to performing a 25 MeV He2+ cyclotron beam irradiation. Raman spectra clearly show the creation of three defects bands (U1 ≈ 530, U2 ≈ 575, and U3 ≈ 635 cm-1) resulting from the ion irradiation and also some changes in the T2g peak of UO2. Their in-depth distribution inside the sample exhibits a clear increase of the damage from the surface up to the position of the implanted He. [ABSTRACT FROM AUTHOR]

This paper is devoted to the determination of the energetically favourable sites of iodine atoms in a zirconium crystal within the density functional framework and using norm-conserving pseudopotentials. We show that the substitutional sites are preferentially occupied compared with the interstitial sites. Our conclusion is that the diffusion process of iodine inside zirconium is of substitutional type in perfect agreement with an experimental study by Carlot. [ABSTRACT FROM AUTHOR]

Abstract: X-ray absorption spectroscopy experiments were performed on a set of uranium dioxide samples implanted with 1017 xenoncm−2 at 800keV (8at.% at 140nm). EXAFS measurements performed at 12K showed that during implantation the gas forms highly pressurised nanometre size inclusions. Bubble pressures were estimated at 2.8±0.3GPa at low temperature. Following the low energy xenon implantation, samples were annealed between 1073 and 1773K for several hours. Stability of nanometre size highly pressurized xenon aggregates in UO2 is demonstrated up to 1073K as for this temperature almost no modification of the xenon environment was observed. Above this temperature, bubbles will trap migrating vacancies and their inner pressure is seen to decrease substantially. [Copyright &y& Elsevier]

Abstract: In this work we focus on experiments involving implantation of 500keV 3He ions in sintered polycrystalline material. Samples are implanted at low fluences (∼2×1013 ions/cm2) and subsequently isothermally annealed in a highly sensitive thermal desorption spectrometry (TDS) device PIAGARA (Plateforme Interdisciplinaire pour l’Analyse des GAz Rares en Aquitaine). The helium fluencies studied are two to three orders of magnitude lower than previous Nuclear Reaction Analysis (NRA) experiments carried out on identical samples implanted at identical energies. The fractional release of helium obtained in the TDS experiments is interpreted using a three-dimensional axisymmetric diffusion model which enables results to be quantitatively compared to previous NRA data. The analysis shows that helium behaviour is qualitatively independent of ion fluency over three orders of magnitude: helium diffusion appears to be strongly inhibited below 1273K within the centre of the grains presumably as a result of helium bubble precipitation. The scenario involving diffusion at grain boundaries and in regions adjacent to them observed at higher fluencies is quantitatively confirmed at much lower doses. The main difference lies in the average width of the region in which uninhibited diffusion occurs. [Copyright &y& Elsevier]

Abstract: Transmission electron microscopy (TEM) observations of UO2 polycrystals irradiated in situ with 4MeV Au ions were performed at room temperature (RT) to better understand the mechanisms of cavity and ultimately fission products nucleation in UO2. Experiments were carried out at the JANNuS Orsay facility that enables in situ ion irradiations inside the microscope to be carried out. The majority of 4MeV gold ions were transmitted through the thin foil, and the induced radiation defects were investigated by TEM. Observations showed that nano-void formation occurs at ambient temperature in UO2 thin foils irradiated with energetic heavy ions under an essentially nuclear energy loss regime. The diameter and density of nano-objects were measured as a function of the gold irradiation dose at RT. A previous paper has also revealed a similar nano-object population after a Xe implantation performed at 390keV at 870K. The nano-object density was modelled using simple concepts derived from Classical Molecular Dynamics simulations. The results are in good agreement, which suggests a mechanism of heterogeneous nucleation induced by energetic cascade overlaps. This indicates that nano-void formation mechanism is controlled by radiation damage. Such nanovoids are likely to act as sinks for mobile fission products during reactor operation. [Copyright &y& Elsevier]

Abstract: The solubility and speciation of chromium in doped uranium oxide are measured in carefully controlled temperature and oxygen potential conditions using electron probe microanalysis (EPMA) and scanning electron spectroscopy (SEM). The examination of the samples by X-ray Absorption Spectroscopy (XAS) provides evidence that (i) chromium is soluble in the UO2 matrix under the +3 oxidation state only regardless of the sintering conditions which is in accordance with a soluble species of type CrO3/2 and (ii) soluble chromium exhibits octahedral symmetry with 6 atoms of oxygen forming CrO6 patterns in the UO2 structure. In consistency with all available experimental information including previously published data, the solubility of chromium in UO2 corresponding to each two-phase field with either Cr, CrO and Cr2O3 may be described in the ranges 1500°C< T <2000°C and −460< μ O2 <−360kJ/mol using the standard thermodynamic equations governing solubility equilibria. The characteristic parameters of the solubility laws in UO2 for the three chromium phases are derived. [Copyright &y& Elsevier]