•A GPU-accelerated 3D neutron dynamics code (GAND) for PB-FHR is developed.•Conjugate gradient method and three preconditioners are implemented on GPU.•GAND is verified by a benchmark and preliminarily applied to PB-FHR.•The acceleration performance is analyzed and the maximum speedup ratio reaches 21.65 times.Pebble bed fluoride-salt cooled high temperature reactor (PB-FHR) is a kind of novel nuclear energy systems, combining advanced techniques such as coated particle fuel and molten-salt coolant to achieve better safety and economy performance. The compact core of a PB-FHR is geometrically complicated due to the randomly-packed pebble bed with fuel motion in a complex core chamber, which yields a highly detailed core-modeling for accurate neutron dynamics analysis. Three-dimensional fine mesh finite volume method is expected to achieve better accuracy because of its strong geometry adaptability in detailed core-modeling, but is much more time-consuming compared to other methods such as coarse mesh nodal method. A GPU-accelerated 3D fine mesh neutron dynamics code (GAND) is developed, using conjugate gradient method (CG) to solve the time-dependent multi-group neutron diffusion equations in r-z-θ coordinates. The GAND code is verified by a cylindrical reactor benchmark with good agreement, and is preliminarily applied to a PB-FHR core in both static and transient analysis. Speed-up ratio and other performance of GAND code using different equation preconditioners is studied, a best speed-up ratio of 21.65 has been achieved using Neumann polynomials-preconditioned CG.

•Interaction effect of Cr and the container materials in molten FLiNaK salt.•Cr dissolved in molten FLiNaK salt would deposit on the surface of the crucibles and form Cr-rich films.•The Cr-rich film on the graphite crucible was identified to be Cr7C3 with a little amount of Cr23C6.•Cr deposited on the Ni crucible surface would form Ni–Cr alloy by thermal diffusion mechanism.Corrosion tests of pure metal Cr were performed in molten FLiNaK (46.5 mol% LiF-11.5 mol% NaF-42 mol% KF) salt at 700 °C for 500 h using graphite crucible and Ni crucible, in order to investigate the interaction effect of Cr and the container materials in molten salt environments. Results indicate that the container materials accelerated the corrosion process owing to different electromotive potentials between metal Cr and the crucibles, and promoted formation of Cr-rich films on the surface of crucibles. The Cr-rich film on the graphite crucible was identified to be Cr7C3 with a little amount of Cr23C6. Whereas the Cr deposited on the Ni crucible surface and formed Ni–Cr alloy by thermal diffusion mechanism.Corrosion tests of pure metal Cr were performed in molten FLiNaK (46.5 mol% LiF-11.5 mol% NaF-42 mol% KF) salt using graphite crucible and Ni crucible in order to study the interaction effect of Cr and the container materials in molten salt environments.

•Hastelloy N, a Ni-based alloy, is subjected to Te-induced stress corrosion cracking.•Sigma 5(0 1 2) Ni grain boundary (GB) is used to research this GB embrittlement.•Te forms strong and covalent-like bonds with neighboring Ni atoms.•Te induces the GB expansion and thus weakens the interfacial Ni–Ni bonds.•The effect of the Te concentration in GB is studied and compared with that of S.Tellurium (Te) can lead to stress corrosion cracking in Ni-based Hastelloy N alloy. A first-principles investigation is presented to clarify this mechanism by simulating a Σ 5(0 1 2) symmetrical tilt grain boundary (GB) with the existence of Te. In accordance with previous studies, we confirm preferential substitutional occupation of Te in the GB region. Te tends to form strong bonds with the neighboring Ni atoms. However, Te induces the GB expansion due to the mismatch in atom size, and thus weakens the interfacial Ni–Ni bonds which are essential to the GB cohesion. The effect of the Te concentration in GB is also investigated.

An in situ X-ray absorption fine structure (XAFS) experiment has been performed to observe the evolution of gold nanoparticles in the ionic liquid [BMIM][AuCl4], by hard X-ray irradiation. The ionic liquid acts as both a reducing agent and a protective ligand. A synchrotron-based X-ray plays the role of the irradiation source, which induces the reduction of the gold species, as well as being a real time probe for XAFS measurements. From the extended X-ray absorption fine structure (EXAFS) fitting results for a series of spectra of gold L3-edge, it can be seen clearly that there is a single Au–Cl bond breaking process before the formation of Au–Au bonds, which is different from previous reports on the formation of Au nanoparticles by several chemical methods.

The diffusion behavior of tellurium into pure nickel is investigated at different annealing temperatures. The purpose is to understand the diffusion mechanism of Te by studying the influence of Te on the surface morphology and grain boundary of nickel. The results show that the surface morphology, reaction product and penetration of Te are greatly dependent on annealing temperature. The depth of Te penetration increases with the elevated temperature from 500 °C to 1000 °C, and the surface reaction products is NiTe0.67 (Ni3Te2) or mixture of a spot of NiTe0.69. Te diffuses into nickel predominantly along the grain boundary at low temperature (below 900 °C), while the diffusion mechanism of Te turns to lattice diffusion above 1000 °C.

An in situ X-ray absorption fine structure (XAFS) experiment has been performed to observe the evolution of gold nanoparticles in the ionic liquid [BMIM][AuCl4], by hard X-ray irradiation. The ionic liquid acts as both a reducing agent and a protective ligand. A synchrotron-based X-ray plays the role of the irradiation source, which induces the reduction of the gold species, as well as being a real time probe for XAFS measurements. From the extended X-ray absorption fine structure (EXAFS) fitting results for a series of spectra of gold L3-edge, it can be seen clearly that there is a single Au–Cl bond breaking process before the formation of Au–Au bonds, which is different from previous reports on the formation of Au nanoparticles by several chemical methods.