Multi-scale X-ray diffraction study of strains induced by He implantation in UO2 polycrystals

Evolution of extended defects in polycrystalline UO2 under heavy ion irradiation: combined TEM, XRD and Raman study

“…The fit of individual Bragg lines has been performed using the FullProf/Winplotr softwares [9]. The free swelling, which corresponds to the swelling that should be present in the irradiated layer without any substrate reaction, is determined following the methodology proposed by Richard et al [10]. It uses the measured component normal to the sample surface (e zz (hkl)) of elastic strains, in grains oriented along h1 1 1i, h1 10i and h10 0i.…”

Strain relaxation in He implanted UO2 polycrystals under thermal treatment: An in situ XRD study

“…This is a direct consequence of the very limited thickness of the 60 keV He implanted layer as compared to the X-ray penetration depth (see Figure 2). Finally, at least one of the following Bragg lines ({111}, {200}, {220} or their harmonics) should be chosen in the set of Bragg line studied since the out-of-plane strain is in this case the only non-zero component of the strain tensor and is readily proportional to the linear free swelling induced by the ion implantation [19]. As a result of these requirements, {220} and {311} Bragg lines were selected for the UO 2 disk implanted with 60 keV He ions whereas {222}, {440} and {620} were chosen for the analysis of samples implanted with 500 keV He ions.…”

“…Results a. Mechanical model proposed for the implanted layer at room temperature i. Implantation with 60 keV 4 He + ions For UO 2 polycrystals implanted with 60 keV He up to a limited fluence (10 16 ion.cm -²), a wellestablished mechanical model is available [17] [19]. It assumes that ion implantation induces an isotropic swelling which is prevented by the reaction of the non-implanted part of the sample considered as infinite.…”

“…This model has been validated using micro XRD measurements. For three grain orientations ({100}, {110}, {111}), the linear free swelling written s/3 is a linear function of the measured out-of-plane strain [19]; its calculation is therefore straightforward provided that elastic constants are known: In the following, C 11 , C 12 and C 44 are taken as constant whatever the temperature and the irradiation conditions. Values provided by Fritz (i.e.…”

“…Indeed, because of the general difficulty to implant a UO 2 -based sample over its full thickness, measured strains have firstly to be interpreted using mechanical models [17] [18] which take into account this specific geometry. Using this methodology, it is possible to derive a swelling in the implanted layer that is equivalent to that measured on samples doped with short lived α-emitters [19]. Secondly in case of implantation using high energy He ions, the strain profile may not be constant over depth [20].…”