Irradiation Induced Defect Clustering in Zircaloy-2

Abstract

Featured Application: The data and results will be helpful to evaluate the radiation damages in fuel cladding or calandria tube of nuclear power plants.Abstract: The effect of irradiation temperature and alloying elements on defect clustering behaviour directly from the cascade collapse in Zircaloy-2 is examined. The in-situ ioWn irradiation technique was employed to study the formation of <a>-type dislocation loops by Kr ion irradiation at 573 K and 773 K, while the dependence of dislocation loop formationon the presence of alloying elements was investigated by comparing with the defect microstructures of pure Zr irradiated under similar conditions. The experimentally observed temperature dependence of defect clustering was further investigated using molecular dynamics (MD) simulations near the experimental irradiation temperatures. We particularly concentrate on yield and morphology of small defect clusters formed directly from cascade collapse at very low ion doses. Smaller loop size and higher defect yield (DY) in Zircaloy-2 as compared to pure Zr suggests that the presence of the major alloying element Sn increases the number of nucleation sites for the defect clusters but suppresses the point defect recombination. MD simulations at 600 and 800 K revealed that the production of both vacancy and interstitial clusters drops significantly with an increase of irradiation temperature, which is reflected in experimentally collected DY data.

Irradiation-induced hardening of Zircaloy-2 at room temperature under external stress conditions

“…Consequently, the material becomes stronger and more resistant to deformation due to the presence of these <a> loops. The understanding of the role of <a> loops in irradiation hardening is crucial for predicting the mechanical response of Zr alloys under irradiation conditions and for designing materials with enhanced performance in nuclear reactor environments [23][24]. However, for various applied stress levels, the increase in hardness values after 1 dpa irradiation is similar, indicating that the influence of stress is not pronounced.…”

“…However, during prolonged reactor operation, these cladding materials are exposed to harsh conditions, which include continuous interaction with cooling water, as well as be subjected to mechanical stresses brought on by component deformation and tensile strains brought on by the thermal expansion of the UO2 fuel pellets. [4][5]. In such a service environment, cladding must withstand simultaneous exposure to neutron irradiation, mechanical stress, and corrosion due to water or steam.…”

Hydrogen isotope population near dislocations in zirconium from molecular dynamics

“…Interestingly, radiation is often found to enhance diffusion and permeation of hydrogen isotopes in metals [ 3 ]. Solubility and diffusivity are likely to significantly change under reactor conditions due to the formation of irradiated defects such as point defects [ 4 , 5 ] and dislocations [ [6] , [7] , [8] , [9] , [10] , [11] ]. However, these defects trap hydrogen isotopes which does not explain why radiation enhances diffusion.…”

“…There are many different types of dislocations in hexagonal close packed (HCP) α-Zr crystals. Since the main defects created during radiation cascade are vacancies and interstitials [ [4] , [5] ], the [0001]/2 intrinsic and extrinsic dislocations, corresponding respectively to removal (i.e., vacancy segregation) and addition (i.e., interstitial segregation) of a (0002) half plane, are easily formed in irradiated samples. These dislocations are on the basal plane, have an edge Burgers vector of near [0001]/2 normal to the basal plane, and typically cannot easily glide.…”