Early stages of irradiation induced dislocations in urania

Abstract

The early stages of nucleation and growth of dislocations by irradiation in urania is clarified based on the combination of experiments and atomistic calculations. It is established that irradiation induced dislocations follow a five stage process: (i) point defects are first created by irradiation, (ii) they aggregate into clusters, (iii) from which nucleate Frank loops, (iv) which transform into unfaulted loops via Shockley that in turn grow, and (v) finally reorganize into forest dislocations. Stages (i)–(iii) participate in the lattice expansion while the onset of lattice contraction starts with stage (iv), i.e., when unfaulted loops nucleate. Irradiation induced dislocations operate in the spontaneous recombination regime, to be opposed to the thermal diffusion regime. Body of arguments collaborates to this statement, the main one is the comparison between characteristic distances estimated from the dose rate (Vat/(K0×τ))13 and from the diffusion coefficient (D×τ)12. Such a comparison identifies materials under irradiation as belonging either into the recombination regime or not.

Lattice strain in irradiated materials unveils a prevalent defect evolution mechanism

“…In this compound, it has been shown by MD simulations of collision cascades 51 that the primary defects formed during ion irradiation are point defects 52 . Therefore, in order to mimic the ballistic damage without having to compute overlap of collision cascades, the Frenkel Pair Accumulation (FPA) technique was used, since it has already been proven very efficient to emulate irradiation damage in several materials 27,[53][54][55][56] . At different steps of the FPA process, XRD patterns were generated from the MD cells using the Debyer program 57 , as already implemented in SiC 27 and pyrochlores 55 .…”

Irradiation resistance of nanostructured interfaces in Zr–Nb metallic multilayers

“…While small dislocation accumulations are not apparent at this Overall, the accumulation of defects is not a simple matter of density, but rather a complex evolution of defect sizes with two competing processes of accumulation and coalescence. It should be noted that all three stages described above can also be found in other material systems [24].…”

“…To simulate the evolution of irradiation defects over a significant dose range, we adopted the FPA method [24,46,47]. The schematic for the FPA method is shown in Fig.…”

“…In turn, the initial atom site becomes a vacancy site, and the displaced atom becomes an interstitial site, thus creating a Frenkel pair. Since the original method presented by Chartier et al [24] was developed for ceramic systems with large sparse lattices, we included an additional optimization step for the denser metallic system, i.e., Zr-Nb. In this additional step, at each interstitial defect site, the nearest neighbors of the displaced atom are nudged radially up to 2 Å away from the center of the interstitial site.…”

“…Schematics of Frenkel pair accumulation[24] (FPA) method.Invited Paperª Materials Research Society 2019 cambridge.org/JMR 2249 j Journal of Materials Research j Volume Issue Jul 15, 2019 j www.mrs.org/jmr Downloaded from https://www.cambridge.org/core. /www.cambridge.org/core/terms.…”