Adib Samin

Ab initio molecular dynamics study of the properties of cerium in liquid sodium at 1000 K temperature

For liquid-sodium-cooled fast nuclear reactor systems, it is crucial to understand the behavior of lanthanides and other potential fission products in liquid sodium or other liquid metal solutions such as liquid cesium-sodium. In this study, we focus on lanthanide behavior in liquid sodium. Using ab initio molecular dynamics, we found that the solubility of cerium in liquid sodium at 1000 K was less than 0.78 at. %, and the diffusion coefficient of cerium in liquid sodium was calculated to be 5.57 × 10−9 m2/s. Furthermore, it was found that cerium in small amounts may significantly alter the heat capacity of the liquid sodium system. Our results are consistent with the experimental results for similar materials under similar conditions.

The thermodynamic and transport properties of GdCl3 in molten eutectic LiCl-KCl derived from the analysis of cyclic voltammetry signals

Pyroprocessing technology is a promising tool for recycling nuclear fuel and producing high purity gadolinium for industrial applications. An efficient implementation of pyroprocessing entails a careful characterization of the electrochemical and transport properties of lanthanides in high temperature molten salts. In this work, the cyclic voltammetry signals of Gd in molten LiCl-KCl salt were recorded for a combination of three temperatures (723 K, 773 K, and 823 K) and three concentration levels (3 wt. %, 6 wt. %, and 9 wt. %) including concentration levels higher than previously reported and relevant for a realistic application of pyroprocessing for molten salt recycle, and the concentration effects were investigated. Four scan rates (200 mV/s to 500 mV/s) were used for each condition, and the signals were examined using conventional Cyclic Voltammetry (CV) analysis equations and by utilizing a two-plate Brunauer, Emmett, and Teller (BET) model accounting for mass diffusion, kinetics, adsorption, and t...

Analytical solutions of the planar cyclic voltammetry process for two soluble species with equal diffusivities and fast electron transfer using the method of eigenfunction expansions

Cyclic voltammetry is a powerful tool that is used for characterizing electrochemical processes. Models of cyclic voltammetry take into account the mass transport of species and the kinetics at the electrode surface. Analytical solutions of these models are not well-known due to the complexity of the boundary conditions. In this study we present closed form analytical solutions of the planar voltammetry model for two soluble species with fast electron transfer and equal diffusivities using the eigenfunction expansion method. Our solution methodology does not incorporate Laplace transforms and yields good agreement with the numerical solution. This solution method can be extended to cases that are more general and may be useful for benchmarking purposes.

A multi-scale study of the adsorption of lanthanum on the (110) surface of tungsten

In this study, we utilize a multi-scale approach to studying lanthanum adsorption on the (110) plane of tungsten. The energy of the system is described from density functional theory calculations within the framework of the cluster expansion method. It is found that including two-body figures up to the sixth nearest neighbor yielded a reasonable agreement with density functional theory calculations as evidenced by the reported cross validation score. The results indicate that the interaction between the adsorbate atoms in the adlayer is important and cannot be ignored. The parameterized cluster expansion expression is used in a lattice gas Monte Carlo simulation in the grand canonical ensemble at 773 K and the adsorption isotherm is recorded. Implications of the obtained results for the pyroprocessing application are discussed.

Ab initio study of radiation effects on the Li4Ti5O12 electrode used in lithium-ion batteries

Lithium-ion batteries are currently in wide use owing to their high energy density and enhanced capabilities. Li4Ti5O12 is a promising anode material for lithium-ion batteries because of its advantageous properties. Lithium-ion batteries could be exposed to radiation occurring in various conditions such as during outer space exploration and nuclear accidents. In this study, we apply density functional theory to explore the effect of radiation damage on this electrode and, ultimately, on the performance of the battery. It was found that radiation could affect the structural stability of the material. Furthermore, the electrode was shown to undergo a transition from insulator to metal, following the defects due to radiation. In addition, the effect of radiation on the intercalation potential was found to be highly dependent on the nature of the defect induced.

A one-dimensional stochastic approach to the study of cyclic voltammetry with adsorption effects

In this study, a one-dimensional stochastic model based on the random walk approach is used to simulate cyclic voltammetry. The model takes into account mass transport, kinetics of the redox reactions, adsorption effects and changes in the morphology of the electrode. The model is shown to display the expected behavior. Furthermore, the model shows consistent qualitative agreement with a finite difference solution. This approach allows for an understanding of phenomena on a microscopic level and may be useful for analyzing qualitative features observed in experimentally recorded signals.

The role of correlations in the determination of the transport properties of LaCl3 in high temperature molten eutectic LiCl–KCl

Abstract It is important to develop an accurate assessment of fundamental data of lanthanides in high temperature molten salts to enable an efficient application of pyroprocessing. This requires a careful consideration of uncertainties in the reported results. In this study, cyclic voltammetry (CV) tests of LaCl3 in KCl–LiCl molten salt were conducted at low concentration levels in the molten salt at 723 K and at several scan rates. The CV signals were subsequently analyzed through the conventional CV analysis and using a BET-based model through a nonlinear least-squares fitting procedure. It was determined that the parameters of the model were strongly correlated and the support plane procedure was implemented to assign joint confidence intervals for the diffusivity of lanthanum. Accounting for the correlations led to a significant increase in the uncertainty of the reported diffusivity which led to better agreement with the literature. Accounting for the correlations may be important for higher concentration levels.

The effects of radiation-induced demagnetization on the performance of the brushless DC motor in robot servo systems

The implementation of humanoid robots will be very significant in nuclear accident treatment in substitution of humans; however the electronic and mechanical parts in robots could be damaged by large dose of radiation. In this paper we study the radiation-induced degradation of the brushless DC (BLDC) motor in robot servo systems and propose how its performance would change due to Nd-Fe-B demagnetization. An explanation of the mechanisms relevant to the radiation-induced demagnetization of the Nd-Fe-B magnets is given, and an approach using the motor back-EMF to analytically study the radiation induced performance changes of the BLDC motor is also included.

An Analysis of Limiting Cases for the Metal Oxide Film Growth Kinetics Using an Oxygen Defects Model Accounting for Transport and Interfacial Reactions

Abstract This work was motivated by the need to understand the passivation of metal surfaces to provide resistance against chemical degradation, given that corrosion is a major limiting factor in the operational lifetime of metals and their alloys. In this study, a unified analysis for an oxide growth model was presented. The oxide growth model was consistent with the literature and accounted for the transport of oxygen defects through a growing oxide film, as well as the electrochemical reactions of oxygen defects at the metal/oxide and oxide/environment interfaces. A linear potential profile across the oxide film was assumed. The model was analyzed for different rate limiting steps in the physicochemical process and perturbation techniques were utilized when necessary. The investigation yielded the well-known linear, parabolic, logarithmic and integral rate laws and the conditions that led to these rate laws were discussed.

Performance analysis on radiation degraded BLDC motor in robot servo systems

For humanoid robot applications in nuclear radiation environments, not only the electronic and mechanical parts, but also the servo system in robots could be damaged by large dose of radiation. In this paper we study the radiation induced degradation to the brushless DC (BLDC) motor in the robot servo systems and analyze how its performance changes due to radiation induced demagnetization. The radiation demagnetization factor is introduced into the electromagnetic model of the BLDC motor, and the motor performance under the PWM control method is compared with the one without radiation degradation. The result illustrates that the radiation will decrease the motor power and cause controlability loss in the robot servo systems.