•The emergence of two vibration bands on RAMAN spectra linked to irradiation defects.•18O diffusion flux increase after proton irradiation.•A strong kinetics acceleration after irradiation.•Oxidation ...kinetics decrease with the irradiation defect annealing.
The corrosion behavior of Zircaloy-4 fuel cladding in nuclear reactor is affected by irradiation damage. The irradiation effect of the post-transition oxide layer on the Zircaloy-4 corrosion rate has been investigated using protons. As previously observed on pre-transition oxide layer, irradiation defects increase the oxidation rate of the alloy up to around 30 days in autoclave in agreement with the irradiation defect annealing characterized by Raman spectroscopy. The model proposed for pre-transition regime is able to describe the oxidation rate after irradiation of post-transition oxide layers.
UO2 polycrystals were irradiated in the nuclear energy-loss regime, Sn (900 keV I and 2 Mev Au ions) and also with an additional electronic energy deposition, Se (900 keV I and 36 MeV W ions ...simultaneously, i.e. Sn&Se). The strain/stress state exhibited by the irradiated pellets was determined by x-ray diffraction measurements. Results show that both measured strain and estimated stress are lower in the dual-beam irradiated samples, indicating that there is an ionization-induced change in the ballistically-generated-defect spectrum. Furthermore, it is shown that the thin irradiated layers maintain the lattice parameter of the pristine material in the basal plane.
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The radiation damage induced in cerium dioxide CeO2 and cerium-gadolinium mixed oxides (Ce, Gd)O2-x was studied by micro-Raman spectroscopy and diffuse UV-visible reflectance spectroscopy. Sintered ...samples of undoped CeO2 and (Ce, Gd)O2-x for 1 mol% and 5 mol% of Gd2O3 were irradiated at room temperature with 2.5-MeV Ar2+ and 12-MeV Ar4+ ions up to high fluences (i.e. 5 × 1014 cm−2 and 2.1 × 1014 cm−2 respectively). The Raman spectra show that no amorphization of those oxides occurs whatsoever, regardless of the Gd content. No clear change of the damage cross section with the Gd3+ content is deduced from the decay of F2g peak intensity versus fluence. Moreover, the reflectivity spectra show a clear decrease of the band-gap energy and increase of the Urbach energy arising from point defect accumulation. Similar effects are found for 1 mol% and 5 mol% Gd2O3, whereas a larger effect on band tailing is seen for undoped ceria. The respective roles of nuclear collisions and electronic excitations are discussed for both ion energies knowing that the two kinds of measurements do not probe the same sample depth. The substitution of Gd3+ ions for Ce4+ ions is likely reducing the damage and the formation of band tails related to the formation of Ce3+ ions by electronic excitation processes.
Recently, unusual Raman signals were observed in different works conducted on thin zirconia layers grown on zirconium alloys simulating in‐reactor materials after high fluence ion irradiation or for ...samples cut from fuel rods irradiated in nuclear plants. As such, these spectra clearly do not correspond to any known spectrum of a pure standard zirconia phase. Therefore, the analysis conducted in this paper aims to provide a better understanding of these peculiar Raman features. For that purpose, specific ion‐irradiated samples were analysed. In situ Raman spectroscopy was first used to follow the irradiation process. Then, samples were characterized using different excitation wavelengths. Finally, the effects of oxygen isotopic substitution were examined in details. Results are discussed in terms of disorder and size‐related effects.
Recently, unusual Raman signals were observed in different works conducted on thin zirconia layers grown on zirconium alloys simulating in‐reactor materials after high fluence ion irradiation or for samples cut from fuel rods irradiated in nuclear plants. The analysis conducted here aims providing a better understanding of these peculiar Raman features. For that purpose, specific ion‐irradiated samples were analysed, and the effects of oxygen isotopic substitution were examined. Results are discussed in terms of disorder and size related effects.
When B4C boron carbide is irradiated in neutron reactors, high quantities of helium are produced due to the 10B(n,α)7Li neutron absorption reactions. It is well known that most helium remains in the ...material, this inducing swelling and cracking. However very few studies deal with the nucleation and growth of the helium clusters. In this paper, B4C is implanted with helium and its behaviour is studied mainly thanks to TEM observations. Different parameters are considered: helium concentration, implantation temperature, post-implantation annealing temperature, width of the implanted zone and overlap with ballistic damage simulating the fast neutron scattering. We observe that helium clusters form either on structural defects (grain and twin boundaries, precipitates) or thanks to irradiation damage induced nucleation. When implanted at low temperature and then annealed, nanometric bubbles form that eventually agglomerate as flat discs associated with strong strain fields. In the temperature range encountered in fast neutron reactors, those discs evolve toward parallel 20–50 nm diameter helium platelets. Grain boundaries are very efficient trapping sites, no evolution of the intergranular helium bubbles is observed up to 1200 °C. In the implanted zone, the platelets change into polyhedron bubbles over 1100 °C with a relaxation of the strain fields together with a strong density decrease. The addition of a ballistic damage increases the density of the helium bubble germs.
Raman scattering is applied to probe the radiation damage in swift heavy ion‐irradiated ceramics, namely zirconium nitride (ZrN), ceria (CeO2), and yttria‐stabilized zirconia (ZrO2: Y, or YSZ) for ...about the same high electronic stopping power of heavy ions. Raman spectra show that these ceramics are radiation‐resistant materials that are not amorphized by such irradiations even for large ion track overlap at high fluences. However, for ZrN, the increase of the TA/LA and TO/LO band intensities versus fluence is evidenced after 100‐MeV Xe ion irradiation up to a saturation for the fluence of 3 × 1012 cm−2. The band growths are ascribed to the increase of the concentration of Zr and N vacancies induced by electronic excitations inside tracks. However, the diffuse reflectance spectra do not exhibit any clear modifications of the electronic structure. For ceria, the decrease and broadening of the main F2g peak of the fluorite‐like structure and the growth of a broad defect band assigned to oxygen vacancy formation is observed versus fluence up to 1014 cm−2 for 200‐MeV Xe ion irradiation. For YSZ, Raman spectra mainly give evidence of the intrinsic lattice disorder due to the native oxygen vacancies even up to high fluences of about 3 × 1013 cm−2 for 200‐MeV I and 200‐MeV Au ion irradiation. Results are discussed on the basis of the interplay between the native structural disorder and the radiation‐induced disorder by electronic excitations in these three materials.
Raman scattering is applied to probe the radiation damage in swift heavy ion‐irradiated ceramics, for about the same high electronic stopping power. For ceria, Raman spectra show that CeO2 is not amorphized by such irradiations even for high fluences. There is a decrease and broadening of the main F2g peak of the fluorite‐like structure and the associated satellites related to native defects, and the growth of a broad defect band assigned to oxygen vacancy formation.
Abstract
Irradiation induced damage in materials is highly detrimental and is a critical issue in several vital science and technology fields, e.g., the nuclear and space industries. While the effect ...of dimensionality (nano/bulk) of materials on its radiation damage tolerance has been receiving tremendous interest, studies have only concentrated on low energy (nuclear energy loss (S
n
) dominant) and high energy (electronic energy loss (S
e
) dominant) irradiations independently (wherein, interestingly, the effect is opposite). In-fact, research on radiation damage in general has almost entirely focused only on independent irradiations with low and/or high energy particles till date, and investigations under simultaneous impingement of energetic particles (which also correspond to the actual irradiation conditions during real-world applications) are very scarce. The present work elucidates, taking cubic zirconia as a model system, the effect of grain size (26 nm vs 80 nm) on the radiation tolerance against
simultaneous
irradiation with low energy (900 keV I) and high energy (27 meV Fe) particles/ions; and, in particular, introduces the enhancement in the radiation damage tolerance upon downsizing from bulk to nano dimension. This result is interpreted within the framework of the thermal-spike model after considering (1) the fact that there is essentially no spatial and time overlap between the damage events of the two ‘simultaneous’ irradiations, and (2) the influence of grain size on radiation damage against individual S
n
and S
e
. The present work besides providing the first fundamental insights into how the grain size/grain boundary density inherently mediates the radiation response of a material to simultaneous S
n
and S
e
deposition, also (1) paves the way for potential application of nano-crystalline materials in the nuclear industry (where simultaneous irradiations with low and high energy particles correspond to the actual irradiation conditions), and (2) lays the groundwork for understanding the material behaviour under other simultaneous (viz. S
n
and S
n
, S
e
and S
e
) irradiations.
Silicon single crystals were irradiated at room temperature (RT) with single and dual low-velocity (i.e., 900 keV I) and high-velocity (i.e., 27 MeV Fe or 36 MeV W) ion beams in order to study ...synergistic effects between nuclear and electronic energy losses in semiconductors. The damage created by irradiation was quantified by using Rutherford backscattering spectrometry in the channeling mode and Raman spectroscopy, and it was visualized using transmission electron microscopy. Whereas single low-velocity ion irradiation leads to amorphization of the surface layer of Si crystals, the use of a dual low- and high-velocity ion beam prevents this phase transformation. However, a remaining disorder exists, the level of which depends on the ratio of the high- to low-velocity ion fluxes. The higher the ratio (1.6 in the present case), the lower the disorder level, with a 30% integrated disorder instead of 100% upon single low-energy irradiation. These results provide evidence that ionization-induced disorder annealing can occur at RT in Si.
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