Fusion Engineering and Design最新文献

The packing factor is an important parameter for describing the internal structural features in pebble beds, which have a significant influence on the heat and mass transfer behavior and the thermo-mechanical properties of the pebble bed. A comprehensive understanding of the packing structure is essential for the design and optimization of the pebble bed and can promote the application of the pebble bed. In this work, an improved line-based averaging method was proposed to calculate the local packing factor or local porosity distribution and validated by comparing the results with those obtained from experimental and numerical studies of cylindrical packed pebble bed. Furthermore, the local packing factor distributions in the angular-radial plane of the cylindrical pebble bed were revealed for the first time. In addition, the line-based averaging method has been applied to reveal the local packing factor distributions in the annular pebble beds, U-shaped pebble beds and hexagonal pebble beds. The main feature of this method is the ability to calculate and plot contour maps of local packing factor or porosity distributions for columnar pebble beds of arbitrary shapes, especially the local packing factor distributions in the cross-sectional plane and the angular-radial plane.

In the solid breeder of deuterium-tritium (D-T) fusion reactor, tritium breeding stems from the reaction between Li atoms and neutrons. Due to the D-T fusion reactor has not been built yet, the accelerator-type fusion neutron source could be applied to tritium production experiments. The tritium yield is currently observed to be at a limited level. For measuring low-concentration tritium, the common method is to collect the tritium released from the breeder by the bubblers and then measure it with the liquid scintillator counter (LSC). Therefore, the selection of bubblers is crucial for effective tritium collection and accurate results of tritium release behavior. To maximize tritium collection, this study initially investigated the performance of different liquid volumes in bubblers utilizing standard tritiated water (HTO) and subsequently validated these selections through experiments involving tritium release of Li₂TiO₃ breeders irradiated by the accelerator-type fusion neutron source. The results demonstrated that the bubbler of total volume 60 ml filled with 20 ml liquid exhibited excellent tritium collection efficiency and repeatability, with the saturation coefficient close to 1. The selected bubbling system with catalytic oxidation was used to identify the different forms of tritium release from the tritium breeder irradiated by fusion neutrons. Neutronic simulation results further confirmed that the selected bubbling system had nearly 100 % collection efficiency. The simulated total amount of tritium released was consistent with the measured value of the bubbling system and LSC. These findings provide technical support for the study on the tritium release behavior of solid breeders irradiated by fusion neutrons.

Alloying is widely used to improve the radiation resistance of plasma-facing materials. The first-principles method based on density function theory was used in this work to study the stability and mobility properties of the W-V mixed dumbbell pair. The diffusion of monovacancy and recovery of mixed dumbbell pairs were also studied. The rotations and diffusion results indicated that the W-V mixed dumbbell pair diffusions are favored in two/three-dimensional motion because of low energy barriers. And the results are also suggested the mixed dumbbell lowers the diffusion energy barriers of the monovacancy. New vacancy diffusion modes were also observed along the 〈110〉 direction during the simulation. Besides, the addition of V may also moderate the diffusion of W SIA in 〈111〉 direction.

The analysis of the gas expansion in the test bench of the ITER DMS Support Laboratory is discussed. For this purpose, numerical FEM simulations were performed during the design phase of the laboratory. These are compared with experimental data, that have been obtained after the construction of the test bench was finished. The numerical and experimental results have been found to agree well. Both indicate the emergence of pressure waves in the acceleration barrel. These contribute to the pellet detachment from the barrel wall. Supersonic velocities have been also observed in the simulations, and an indirect indication for their presence has been found in the experimental results. The main processes during the propellant gas expansion inside the propellant gas recovery chamber are discussed, and a rough estimate for the amount of gas entering the flight tube of the test bench before the pellet is presented.

Tritium is inevitably produced in a fusion neutron source facility, A-FNS, mostly via D-Li nuclear reactions. In the design activity of the A-FNS, radiological risk assessment for the public due to the tritium released from the facility is indispensable. We have developed a new dose assessment code, ROkkasho PUff COde (ROPUCO), which employs a Gaussian Puff model with considering tritium re-emission from soil for precise tritium dose assessments. In this study, ROPUCO was validated by benchmarking the experimental results for the Chalk River in 1987 and another tritium dose assessment code, ACUTRI. The results showed that ROPUCO could properly simulate tritium dispersion in the atmosphere under flat topography and uniform meteorological conditions.

Liquid lithium plasma facing components (PFCs) may provide an attractive alternative to more conventional solid PFCs due to improved plasma performance and the reduction of erosion and wall damage issues. Conceptual designs for liquid lithium divertors have been proposed, but a complete understanding of the interaction between liquid lithium and structural materials will be required for their successful implementation. One aspect of the interaction is the wetting of different materials by liquid lithium at temperatures relevant to fusion applications.

Contact angle measurements were used to study the wetting of liquid lithium on 304 stainless steel with varying surface roughnesses, metallic coatings, advanced alloys, and insulating materials in the temperature range from 200 °C to 350 °C. A mirror finish on 304 stainless steel was found to decrease the contact angle and lower the critical wetting temperature while all rougher 304 stainless steel treatments behaved similarly. For thin film coatings and other alloys, the surface roughness was found to impact the wettability more than the change in chemical composition. Compatibility issues with all three insulating materials tested are discussed and limited contact angle data was collected for these samples.

The magnet power supply system is one of the important subsystems of nuclear fusion devices. Although it has undergone strict safety and stability verification before design and operation, the experimental conditions at the work site still have uncertainty. The fast discharge unit may not be able to open and the magnet power supply may have a ground fault. Therefore, it is necessary to systematically analyze the above possible fault conditions, in order to better protect the superconducting magnet. In this paper, the quench protection system and grounding protection system of TF coil magnet power supply are theoretically analyzed and calculated. According to the calculation results, the TF coil fault simulation model is built in MATLAB/Simulink, and the influence of the fault state of the power supply on the magnet is systematically analyzed. The results show that the maximum voltage at fault is much higher than the rated voltage during operation, so a larger margin should be considered in the design process to protect the superconducting magnet. The research in this paper has certain guiding significance for the design of fast discharge unit and TF magnet coil grounding system, and plays an important role in the performance and safety of fusion device operation.

A production mechanism for negative hydrogen ions using cesium coated tungsten dust particles in hydrogen plasma has been established at the Centre of Plasma Physics – Institute for Plasma Research (CPP-IPR). A new experimental setup has been developed for the production, extraction and acceleration of such H⁻ ions. The extraction and acceleration of H⁻ ions in this system require a high voltage supply and a floating configuration based plasma source. Due to the high complexity and safety concerns associated with the experimental system, a reliable and robust instrumentation and control system has been developed and is presented in this work. To monitor and control various experimental parameters, a PXI-based event-driven interlock and a requirement-based continuous data acquisition and control system have been designed, developed, and commissioned, incorporating fiber optic links. The software for the control sequences, including monitoring and acquisition, has been developed and implemented on a Real-Time Controller using LabVIEW 2020. The system has been tested, and some experiments have been conducted. Experimental results, along with the test results of the system components, are presented in the paper.

Numerical analysis provides the design choice and operating window of liquid metal Plasma Facing Components (PFC) concepts. Coupled analysis of boundary plasma together with the surrounding boundary structures is required. To achieve this goal, PPPL is developing a comprehensive multi-physics model for modeling of PFCs in fusion devices. The model includes the fluid-kinetic code SOLPS-ITER and the flow and heat transfer code CFX from ANSYS. SOLPS-ITER was augmented with a liquid metal boundary condition algorithm, allowing direct two-way coupling of the plasma analysis with the two-dimensional analytical slab flow model which includes heat convection in the liquid metal PFC. The target heat flux resulting from this coupled analysis is used as a boundary condition for detailed 3D Computational Fluid Dynamics (CFD) Magneto Hydro Dynamics (MHD) and heat transfer analysis. A new formulation of MHD equations is introduced in the numerical procedure ensuring current conservation of the discretized equations. Results of the 3D analysis are used for final validation of the coupled model. A PFC design where a porous wall is used to stabilize the liquid metal surface, while MHD drive is used to push the liquid metal flow inside the PFC, will be investigated in the regimes where vapor shielding is created for enhanced volumetric plasma heat dissipation.

This study proposes a 2PUU-2PSS parallel mechanism (PM) designed to meet the high-precision assembly requirements of the DEMO vacuum vessel. The mechanism, featuring four degrees of freedom (3T1R), is capable of moving to the working area with the assistance of a conveying device to perform high-precision cutting and welding operations on the inner walls of the vacuum vessel. Firstly, the number and characteristics of the mechanism's degrees of freedom are analyzed based on screw theory, where the correctness of the design is verified. Secondly, with the constraint of the mechanism's rod length, the forward and inverse kinematics equations are established. The forward kinematics equations are then transformed into unconstrained optimization equations, and a differential evolution algorithm is employed for solving. Furthermore, to enhance the optimization efficiency and robustness of the differential evolution algorithm, a mean-based dual mutation strategy and an individual selection strategy are proposed and integrated into the traditional differential evolution algorithm, forming a Mean-based Dual Mutation Differential Evolution (MDDE) algorithm with strong global search capabilities and convergence rates. To assess the performance of the MDDE algorithm, numerical experiments are conducted using two CEC Benchmarks functions and two mechanical examples. The experimental results demonstrate that the MDDE algorithm consistently outperforms the compared algorithms. Finally, numerical examples are provided to demonstrate the application of the MDDE algorithm in obtaining the forward kinematics solution, including the single-point position and orientation and continuous trajectory, for the 2PUU-2PSS PM, where the correctness of the forward kinematics solution is verified through the application of the inverse kinematics.