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

Abstract

Within the frame of the long-term evolution of spent nuclear fuel in dry disposal, the behavior of He in UO 2 polycrystals has to be studied. In this paper, strain relaxation in He implanted samples have been characterized using in-situ X-ray diffraction during thermal annealing. The influence of a wide range of experimental parameters (annealing atmosphere, He ion energy, orientation of the UO 2 grains probed by X-rays) has been evaluated. If each of them contributes to the strain relaxation kinetics in the implanted layer, strain relaxation is not completed for temperatures below 900 °C which is equivalent to what has been found on He implanted UO 2 single crystals, or aged UO 2 pellets doped with α-emitters. This stands for an additional evidence of the interest of ion implantation to simulate self-irradiation in spent nuclear fuel. Moreover, in the case of implantation with 500 keV He ions, we clearly show that strain relaxation and He release are not correlated for temperatures below 750 °C and demonstrate that this applied in-situ approach is well-suited for measuring strains in ion implanted polycrystals.

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

“…This is consistent with the temperature dependence of the free swelling. Indeed, Palancher et al [26] showed for UO 2 pellets irradiated with He and then annealed, a decrease of the e zz (hkl) within the range [300-500°C] of annealing temperature. It seems that, in the vicinity of 500°C, there is an annealing of a given kind of swelling defects.…”

Strain profiles in ion implanted ceramic polycrystals: An approach based on reciprocal-space crystal selection

“…they are made a large domains with a slight (below 1°) misorientation. If the interest of the work is demonstrated by the analysis of 1D XRD patterns, the analysis of the full reciprocal space scattering (2D 32 an ultimately 3D) should be very helpful for determining the size of extended defects in polycrystals implanted in severe conditions (high energy ions 33 and/or high damage values 34 ). Finally this work can be considered as first step towards the use of coherent X-ray diffraction to characterize strains in ion implanted polycrystals 35 .…”

Mechanical behaviour near grain boundaries of He-implanted UO2 ceramic polycrystals

“…The implantation induces strains in a thin surface layer. In-depth characterisation using monochromatic X-ray techniques estimates the strained layer thickness to 0.4 µm [13] and 1.3 µm [14] for 60 keV and 500 keV respectively. These values are in agreement with the damage profiles estimated using SRIM software [15] for these conditions.…”

“…The proposed method has thus been improved [11]: new image analysis procedures, combined with statistical tools were developed to reduce the measurement error by a factor 2 and to correct detection errors. With the increase of the implantation energy, the strain in the implanted layer varies along the depth [14], changing the shape of the double Laue spot shown in Figure 1. A specific work has been done [16] to face this problem: for high energies (for example 500 keV), the strain measured on the Laue patterns corresponds to a mean value over the implantation layer.…”

“…where s/3 denotes the linear free swelling, which can vary with the implantation depth z [13,14]. This swelling loads mechanically the sample surface, producing stress and strain fields.…”