During the fission cycle in molten salt reactors insoluble noble metals of the platinoid group are formed. From the initial molten salt reactor experiment it is known that these metal particles tend to adhere to walls within the molten salt reactor. As the particles along the decay chain are often unstable, these depositions onto surfaces can cause decay hot-spots and are particularly dangerous in the case of loss-of-coolant scenarios. To get a better understanding of different metals’ adherence behaviour, the contact angle between the metal and the molten salt can be used. The contact angle is a measure for wettability; this property gives information about whether the metal particle prefers staying dispersed in the molten salt or exhibits a propensity to adhere to the reactor surfaces.

To measure the contact angle between a molten salt and different materials intended for use in a reactor, a setup was designed and constructed to allow the optical measurement of said contact angle. The goal of this project is the commissioning of the setup, and the proof of concept of the envisioned measurement method. A thorough study will be conducted to get a full overview of the wettability behaviour of molten salt on the different noble metals occurring in the molten salt reactor. The results obtained can provide valuable information about if and where in the molten salt reactor particle adhesion is to be expected. This information will be valuable on the path to fully safe molten salt reactors.

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In this project, you will develop OpenFOAM simulations to investigate thermophoretic effects on particle deposition in molten salt reactors. The migration and deposition of solid fission products represents a significant area of study for reactor safety and performance analysis. You will implement an Eulerian-Lagrangian framework, where the molten salt is treated as a continuous phase (Eulerian) while fission product particles are tracked individually (Lagrangian). This approach enables detailed analysis of particle transport phenomena within the complex fluid dynamics of the reactor. Your simulations will utilize powerful coupled OpenFOAM solvers, in which the discrete particles and the continuum fluid influence each other.

The project requires implementation of several physical models to accurately capture particle behavior. You will incorporate Brownian motion to represent random thermal fluctuations affecting small particles. DLVO theory with compressed double layer potential will be applied to model electrostatic interactions. Van der Waals attractive forces will be included to simulate agglomeration and nucleation processes that influence particle size distribution and transport characteristics. You will analyze the effects of temperature gradients on particle movement, specifically investigating thermophoretic forces that drive particles from high to low temperature regions within the reactor. Gravity-driven sedimentation will be modeled as a competing transport mechanism.

Through this work, you will contribute to the fundamental understanding of fission product transport in molten salt environments, providing insights that may inform future reactor designs and safety analyses.

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Molten Salt Reactors (MSRs) use molten salt mixtures as primary coolant, often with dissolved fissionable fuel compounds. These salts' high heat capacity and boiling point enable near-atmospheric pressure operation, unlike light water reactors (LWRs), while their thermal expansion coefficient provides inherent safety.

The U- and Th-based fuels produce three types of fission products: salt seekers (soluble compounds carried in the salt), noble gases (which bubble away), and noble metals. These noble metals form insoluble nanoparticles (SFPs) that sediment on reactor surfaces, creating potentially dangerous decay hot-spots during loss-of-coolant scenarios.

To study this SFP sedimentation, we're developing an experiment using Molecular Dynamics (MD), which excels at simulating particle interactions by tracking individual particle motion and forces. MD's detailed tracking of particle behavior will help understand both microscopic interactions and macroscopic phenomena in molten salt mixtures.

The project will involve creating a numerical model to capture metallic nanoparticle dynamics based on MD principles. First, an investigation into the scale of these dynamics must be performed. The interactions between the metallic nanoparticles and surface interactions involve several non-trivial forces and interaction potentials (such as DLVO theory), which must be studied and implemented in great detail. It will be imperative to incorporate the Polarizable Ion Model (PIM) into the simulations to properly capture the microscopic behavior of the particles with respect to the ‘free’ ions in the molten salt mixture. This project will be part of a larger hybrid MD-Lattice Boltzmann model that will simulate the granular particle and material interactions as well as larger flow phenomena in molten salt loops.

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Molten Salt Reactors (MSRs) use molten salt mixtures as primary coolant, often with dissolved fissionable fuel compounds. These salts' high heat capacity and boiling point enable near-atmospheric pressure operation, unlike light water reactors (LWRs), while their thermal expansion coefficient provides inherent safety.

The U- and Th-based fuels produce three types of fission products: salt seekers (soluble compounds carried in the salt), noble gases (which bubble away), and noble metals. These noble metals form insoluble nanoparticles (SFPs) that sediment on reactor surfaces, creating potentially dangerous decay hot-spots during loss-of-coolant scenarios.

To study this SFP sedimentation,  we need to first design and construct a test facility that is based on water, and then do experiments that are used to compare with simulations. The project consists of the following steps:

An exploratory phase, where you try to determine exactly what you want from your facility and what it will roughly look like. This includes investigating transport phenomena, different flow regimes, the velocities of the injected gas, the influence of geometry, and so on. This phase can be somewhat rough and approximate.

A design phase, where you develop the detailed design of the setup. This will be done in consultation with our technicians and the institute’s workshop. You won’t be on your own during this part; working collaboratively will be highly beneficial.

An experimental phase, where you use your setup to perform measurements. Here, you will carry out what you planned in advance: what do you want to learn from your setup? What specific insights can you gain?

There is also a numerical phase, though it’s harder to separate from the rest as a distinct stage. Before starting construction, it’s useful to conduct some numerical validation to test your ideas. Additionally, you may need to update your numerical models based on measurements that reveal unexpected phenomena.

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The transition from fossil fuels to sustainable energy sources can only be achieved with targeted upgrades in energy storage technology. Conventional batteries are limited in capacity by their volume. To address this, redox flow batteries were introduced, decoupling energy storage from the physical size of the battery cell. However, the poor solubility of redox species restricts the energy density achievable with this technology.

To overcome this limitation, this project will investigate a novel energy storage method known as a redox-mediated battery. Part of the project will involve setting up a simple experimental system to study redox-mediated reactions and to capture various kinetic and diffusion parameters. To decouple the effects of individual parameters, a model will be developed and validated against experimental results.

The initial step will focus on simple redox-mediated reactions without any mass transfer limitations impeding the reaction, progressing to more complex systems involving additional mass transfer limitations as the project advances. These findings will directly contribute to building both a numerical model (in Julia preferably) and an experimental setup for testing this novel battery technology. You will gain hands-on experience in both the experimental testing of batteries and modeling the transport phenomena involved.

If time permits, an extension of the project could involve investigating the spatial dependence of the reaction rate within the system using SEM (Scanning Electron Microscopy) analysis.

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n a Molten Salt Reactor, solid fission particles tend to sediment on a surface, such as the reactor vessel and heat exchagers, deteriorating the properties of the structural materials in the reactor. In this unique project, the PhD student will study the sedimentation of these particles and its underlying mechanisms in high temperature molten salts. The approach is to develop an experimental facility, where parameters such as temperature, flow and materials can be changed and to extract data on the tendency of solid fission products to sediment under a range of conditions. The acquired data will then be used to validate own-developed numerical and physical models for sedimentation, so that a solid calculated estimate can be made in real cases and real situations. This PhD project is part of the recently granted EC project "ENDURANCE", which is a follow-up project of SAMOFAR and SAMOSAFER, both projects focussed on thorium-based molten salt reactors.
The PhD student will be part of this international consortium and cooperate with the other members of the project, the technicians in our research group and with the principle investigator. Start-date of the project is October 1, 2024.
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LBM is mostly used for fluid flow and scalar transport (heat, species). A lesser known feature, however, is the fact that the method can also be used for neutron transport and be coupled to momentum and energy transport. Recently, researchers have extended the method for neutronics. In this project, the method will be applied to either a molten-salt reactor case or the DIPR, a reactor in which radio-isotopes can be produced. If you are interested, we can start a discussion on the exact topic to be done.

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The molten salt reactor is a very safe and sustainable nuclear reactor. One of the key safety features is the freeze plug, which can be used in case of an emergency situation. The plug is kept frozen actively and melts as soon as the active freezing stops (e.g. by a station blackout). The plug needs to melt quickly to drain the reactor vessel as fast as possible. The angle of the freeze plug is important because the melting occurs partially by natural circulation. Hence, the orientation of gravity with respect to the plug is important.

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The molten salt reactor is a very safe and sustainable nuclear reactor. The reactor fuel is liquid instead of solid, making this type of reactor very safe. Freezing may occur in the heat exchanger, risking blockage of the cooling channels. To understand freezing under turbulent conditions, one needs either perform experiments or simulations. This project deals with LES simulations under turbulent conditions, thereby using the lattice-Boltzmann method. This method can easily be implemented on GPU's, so that large calculations speeds can be accomplished. Challenges in this project are the development of such an efficient code in the Julia language, in conjunction with Large Eddy Simulations (to model the turbulence).

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During the operation of molten salt reactors valuable fission products are formed. Due to the extreme working environment, a removal of those particles is challenging. One promising technology to remove fission products is the separation via helium bubbling. Here, the fission particles are adhering to the helium bubbles, from which they are getting transported to the liquid surface, from where they can get separated. Part of the research is building up a setup for experiments with molten salts, in which the flow characteristics and particle removal are determined by methods like the Laser-Doppler-Anemometry and Particle Image Velocimetry. In a first step, experiments will be conducted at room temperature in water and a model system consisting of water/glycerol, which is well established to mimic the characteristics of the molten salt. From these results, operating conditions will be determined, which will be used in a later step with the molten salt setup at elevated temperatures. Moreover, numerical work in the form of CFD-simulations can be included to obtain additional information about the phenomena inside the reactor.

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Supercritical fluids are being used in a wide range of applications such as chemical processes (e.g. extration) and energy processes (e.g. heat removal, nuclear reactors). In this study, the student is going to use and extend the lattice-Boltzmann Method for supercritical fluids and study the phenomenon of natural convection under laminar (and perhaps) turbulent conditions.

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