Interactions between alloy elements and oxygen at the steel-liquid LBE interface determined from first-principles molecular dynamics simulations.

Lead bismuth eutectic (LBE) alloy shows high potential for application in advanced nuclear systems such as lead-alloy-cooled fast reactors. However, high-temperature LBE liquid is prone to corrode the reference containment material, typically made of steel, through a process known as liquid metal corrosion. In this work, an extensive set of first-principles calculations was performed to investigate the diffusion behavior of steel alloy elements and O in liquid LBE. The results showed Bi atoms diffusing a little bit faster than Pb atoms, and the Ni atoms in steel being most likely to dissolve into the LBE. Compared to Cr atoms, Fe atoms were calculated to diffuse more slowly, and Ni atoms more rapidly. In the presence of Al and/or Si, Al-O and Si-O pairs were calculated to be more stable than Fe-O/Cr-O pairs and to be inclined to form protective stable Al/Si related oxides. The Ni-O distance and pair formation energy in LBE indicated the Ni-O pair to be inclined to decompose over a period of time. We expect these data to be used as indispensable information for understanding the dissolution and oxidation corrosion behavior of steels in liquid LBE.

Evolution of Dislocation Loops Induced by Different Hydrogen Irradiation Conditions in Reduced-Activation Martensitic Steel.

Hydrogen can be induced in various ways into reduced-activation ferritic/martensitic (RAFM) steels when they are used as structural materials for advanced nuclear systems. However, because of the fast diffusion of hydrogen in metals, the effect of hydrogen on the evolution of irradiation-induced defects was almost neglected. In the present work, the effect of hydrogen on the evolution of dislocation loops was investigated using a transmission electron microscope. Specimens of reduced-activation ferritic/martensitic (RAFM) steels were irradiated with hydrogen ions to 5 × 1020 H⁺ • m-2 at 523⁻823 K, and to 1 × 1020 H⁺ • m-2 - 5 × 1020 H⁺ • m-2 at 723 K. The experimental results reveal that there is an optimum temperature for dislocation loop growth, which is ~723 K, and it is greater than the reported values for neutron irradiations. Surprisingly, the sizes of the loops produced by hydrogen ions, namely, 93 nm and 286 nm for the mean and maximum value, respectively, at the peak dose of 0.16 dpa under 723 K, are much larger than that produced by neutrons and heavy ions at the same damage level and temperature. The results indicate that hydrogen could enhance the growth of loops. Moreover, 47.3% 1 2   a0 <111> and 52.7% a0 <100> loops were observed at 523 K, but 1 2   a0 <111> loops disappeared and only a0 <100> loops existed above 623 K. Compared with the neutron and ion irradiations, the presence of hydrogen promoted the formation of a0 <100> loops.