Development of new materials for current and advanced reactor concepts is hampered by long lead times and high cost of reactor irradiations coupled with the paucity of test reactors. Ion irradiation offers many advantages for emulating the microstructures and properties of materials irradiated in reactors but also poses many challenges. Nevertheless, there is a growing body of evidence, primarily for light ion (proton) irradiation showing that many, if not all of the features of the irradiated microstructure and properties, can be successfully emulated by careful selection of irradiation parameters based on differences in the damage processes between ion and neutron irradiation. While much less has been done to benchmark heavy- or self-ion irradiation, recent work shows that under certain conditions, the complete suite of features of the irradiated microstructure can be emulated. This study summarizes the contributions of ion irradiation to our understanding of irradiation effects, the options for emulating radiation effects in reactors, and experience with both proton irradiation and heavy ion irradiation.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0884291415000734

Challenges to the use of ion irradiation for emulating reactor irradiation

The formation of voids in an irradiated material significantly degrades its physical and mechanical properties. Void nucleation and growth involve discrete atomic-scale processes that, unfortunately, are not yet well understood due to the lack of direct experimental examination. Here we report an in-situ atomic-scale observation of the nucleation and growth of voids in hexagonal close-packed magnesium under electron irradiation. The voids are found to first grow into a plate-like shape, followed by a gradual transition to a nearly equiaxial geometry. Using atomistic simulations, we show that the initial growth in length is controlled by slow nucleation kinetics of vacancy layers on basal facets and anisotropic vacancy diffusivity. The subsequent thickness growth is driven by thermodynamics to reduce surface energy. These experiments represent unprecedented resolution and characterization of void nucleation and growth under irradiation, and might help with understanding the irradiation damage of other hexagonal close-packed materials.

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In-situ atomic-scale observation of irradiation-induced void formation

Vacancy clustering in zirconium: An atomic-scale study

In this chapter, the effects of neutron irradiation on zirconium alloys are described. Irradiation effects on the microstructure are first discussed, describing damage creation and point-defect evolution leading to loops formation and secondary-phase evolution under irradiation. Then, in the second part, irradiation effects on postirradiation mechanical behavior and deformation mechanisms, especially during tensile test and also after postirradiation thermal treatment or postirradiation creep tests, are given. Finally, the in-reactor deformation behavior, growth, and irradiation creep, as well as the related deformation mechanisms, are analyzed.

Radiation Effects in Zirconium Alloys

Irradiation creep and growth of zirconium alloys: A critical review

HVEM study of the effects of alloying elements and impurities on radiation damage in Zr-alloys

Under irradiation, the acceleration of growth of nuclear reactor components made of Zircaloy is clearly correlated to the presence of component dislocation loops. In the early stages, these loops appear to be essentially located close to the intermetallic precipitates. At higher doses, when component dislocation loops are observed all over the microstructure, analysis of the Zr matrix reveals an homogeneous iron content due to the dissolution of the precipitates. Thus, iron may play a significant role in the nucleation component dislocation loops. A specific study has been performed on Zircaloy thin foils implanted with increasing amounts of iron. The conditions of nucleation and growth of these component dislocation loops have been followed in a 1-MeV transmission electron microscope. The dose level for component dislocation loop nucleation is weakly Fe-content dependent. However, their size and density increase with increasing iron implantation. These results are compared to direct observations made on irradiated reactor components. The role of iron on accelerated growth is then discussed.

C. Regnard

Papers

HVEM study of the effects of alloying elements and impurities on radiation damage in Zr-alloys

Influence of Iron in the Nucleation of ⟨c⟩ Component Dislocation Loops in Irradiated Zircaloy-4