**Dislocation density transients and saturation in irradiated zirconium**

AR Warwick and R Thomas and M Boleininger and Ö Kot and G Zilahi and G Ribárik and Z Hegedues and U Lienert and T Ungar and C Race and M Preuss and P Frankel and SL Dudarev, INTERNATIONAL JOURNAL OF PLASTICITY, 164, 103590 (2023).

DOI: 10.1016/j.ijplas.2023.103590

Zirconium alloys are widely used as the fuel cladding material in pressurized water reactors, accumulating a significant population of defects and dislocations from exposure to neutrons. We present and interpret synchrotron microbeam X-ray diffraction measurements of proton -irradiated Zircaloy-4, where we identify a transient peak and the subsequent saturation of dislocation density as a function of exposure. This is explained by direct atomistic simulations showing that the observed variation of dislocation density as a function of dose is a natural result of the evolution of the dense defect and dislocation microstructure driven by the concurrent generation of defects and their subsequent stress-driven relaxation. In the dynamic equilibrium state of the material developing in the high dose limit, the defect content distribution of the population of dislocation loops, coexisting with the dislocation network, follows a power law with exponent alpha approximate to 2.2. This corresponds to the power law exponent of 6 approximate to 3.4 for the distribution of loops as a function of their diameter that compares favourably with the experimentally measured values of 6 in the range 3 <= 6 <= 4.

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