Vacuum Vessel Of Fusion Reactor Research Articles

EBSD Analysis of 316L Stainless Steel Weldment on Fusion Reactor Vacuum Vessel

EBSD Analysis of 316L Stainless Steel Weldment on Fusion Reactor Vacuum Vessel

Design and Multi-Objective Optimization of a Dexterous Mobile Parallel Mechanism for Fusion Reactor Vacuum Vessel Assembly

The present paper proposed a newly designed dexterous mobile parallel mechanism for fusion reactor vacuum vessel assembly, the robot system has advantages in terms of compact design, the capability to carry out heavy-duty machining tasks, is easy to evacuate, and has less space occupation than other robot systems in existence. Despite different robot systems having been studied in the fusion reactor, there is still a lack of research on mechanism development for vacuum vessel assembly, which is attractive to future fusion reactors. In the fusion reactor, the robot systems will carry out different tasks, such as welding and machining. The assembly tasks of the vacuum vessel will be performed from inside of the vacuum vessel on-site. Then the paper introduced the single-objective and multi-objective optimization design of the proposed mechanism, the optimized objective was considered to be a combination of parallel mechanism dynamic machining force, dexterity, stiffness and workspace volume. The design variables were derived from the geometry of the fixed and movable platforms, which include mass, inertia, the sizes of the platforms, and distances between universal joints located on the platforms. In the multi-objective optimization, non-dominated sorting genetic algorithm II was adopted and different trajectories were designed to simulate the machining process, which further turns the local optimization problem into a global optimization problem. Finally, the optimized results were extracted and analyzed. Simulation results indicated the effectiveness of the proposed multi-objective optimization approaches and multi-objective optimization was found to be more reliable than single-objective optimization.

Design and implementation of a mobile parallel robot for assembling and machining the fusion reactor vacuum vessel

Abstract The present paper introduces a mobile robot machine for the fusion reactor and presents its implementation. The task of the robot is to carry out assembly work inside the fusion reactor vacuum vessel, the assembly work consists of scanning, machining, splice plate transportation, welding, nondestructive testing (NDT), defect welding point cutting and re welding. To better meet the requirements of the fusion reactor configuration, the structure and the kinematics of the mobile parallel robot have been optimized for the fusion reactor access. In this paper, the overall design of the mobile parallel robot is first presented, followed by calculation and simulation of the static, kinematic and workspace model of the mobile parallel robot. Finally, the implementation process of the mobile parallel robot is introduced. Compared with the similar mobile parallel robot developed by the same research group and demonstrated in ITER, the new designed robot machine is more reliable and more easily realizable, and, moreover, it is suitable for assembling work in different environments.

Dynamic analysis and control of a Fusion Reactor Vacuum Vessel Assembly Robot

Abstract The assembly of vacuum vessel (VV) is a vital task for the fusion reactor. This paper introduces simulation of a parallel robot built up for the assembly of fusion reactor CFETR (Chinese Fusion Engineering Test Reactor) to carry out welding of adjacent VV sectors using splice plates, and machining in case some sectors need to be replaced for repair. The kinematics and dynamics equations of the robot are obtained, and a non-singular terminal sliding mode controller is designed which overcomes the drawbacks of the conventional linear sliding mode control. The stability of the system is verified using the Lyapunov stability criteria. The proposed method is tested by defining a trajectory for the robot’s end-effector and simulating the multi-body model of the robot.

Correlation between microstructure evolution and mechanical properties of 50 mm 316L electron beam welds

The electron beam welding technique will be used for the development of fusion reactor vacuum vessel with thicker stainless steel material (50 mm). The through thickness microstructure and mechanical properties for electron beam welded 50 mm thick 316 L austenitic stainless steel were evaluated by microstructural analysis and mechanical tests. The results reveal that microstructure and mechanical properties of joint is non-uniform through transverse and lengthways contrast. Owing to the change of ferrite content and grain size, the microhardness and tensile strength is weaker in fusion zone (FZ) by compared with the base metal (BM). Besides, the bottom part of FZ shown higher strength, microhardness as well as impact resistance than middle and top parts which may be attributed to the grain refining from top to bottom part. Experiments results proved the yield strengths (YS), ultimate tensile strengths (UTS) are positively associated with Vickers hardness. Furthermore, as the thickness increases, the high cooling rate led to the change in the solidification behavior from primary ferrite with second-phase austenite (FA) to primary austenite with the second-phase ferrite (AF) which is accompanied by a decrease in ferrite number.

DNS Study of Dust Particle Resuspension in a Fusion Reactor Induced by a Transonic Jet into Vacuum

This paper reports on a two-phase flow Direct Numerical Simulation (DNS) aimed at analyzing the resuspension of solid particles from a surface hit by a transonic jet inside a low pressure container. Conditions similar to those occurring in a fusion reactor vacuum vessel during a Loss of Vacuum Accident (LOVA) have been considered. Indeed, a deep understanding of the resuspension phenomenon is essential to make those reactors safe and suitable for a large-scale sustainable energy production. The jet Reynolds and Mach numbers are respectively set to 3300 and 1. The Thornton and Ning impact/adhesion model is adopted and improved. An advanced resuspension model, which takes into account the dynamics (rolling and slipping) of particles at the wall, is implemented. The use of this model combined with a DNS represents a great novelty in simulating the particle resuspension process. The particles initially deposited at the wall have constant density, whereas their diameters are drawn according to a log-normal distribution, with parameters obtained from experimental data. It has been found that the flow induced motion of wall deposited particles is highly linked with the instantaneous fluid structures and the resuspension phenomenon predominantly affects particles with the largest diameters. Moreover, the jet-deposit interaction is mostly confined within a circumference around the jet of radius approximately equal to the jet diameter.

Oxidation studies of Indian reduced activation ferritic martensitic steel

The paper reports the oxidation behaviour of Indian variety of reduced activation ferritic martensitic steel (RAFMS) proposed to be used as a first wall material in test blanket module in ITER and future fusion reactors. Oxidation of first wall can occur in case of a catastrophic leak in the vacuum vessel of fusion reactor. The oxidation of Indian RAFMS was done at 450–650 °C. Long-term oxidation for 25, 50 and 100 h was studied at 550 °C. A mass gain/unit area vs time was plotted and oxidation kinetics determined. The cross section SEM of the oxidised RAFMS was done. The SEM micrographs showed two distinct layers of oxides that have formed with total thickness of around 10 µm. Glancing-angle XRD showed that the top layer is essentially a mixture of magnetite and haematite. A strong enrichment of Cr is visible in a narrow band below the top layer near the scale/alloy interface. It was found that formation of this Cr-rich spinel mid-layer ensures the short-term and long-term oxidation resistance of IN-RAFMS in case of any accidental leak in fusion reactor conditions.

Radial Profile of Plasma Flow Parameters Following Evolution of Electrothermal Polycarbonate Plasma into a Large Chamber Simulating Impurity Expansion in Fusion Reactor Vacuum Vessel

The 2-D evolution of the plasma as it expands outside the capillary source, which simulates ablation of plasma-facing materials due to high-heat flux deposition, is of importance to investigate the plasma flow scaling laws with inclusion of radial variations. The flow continues from the source exit through a converging–diverging transition region and expands into a large expansion volume that simulates the vacuum chamber of a tokamak fusion reactor. This 2-D modeling resolves the problem of the 1-D steady state analysis of the plasma bulk flow that assumes the flow parameters to vary only in the axial direction with a uniform radial distribution. As the plasma expands towards the sidewalls of the diverging section in the transition region, the bulk plasma has a finite chance to lose energy primarily in the form of heat loss, which might cause readjustment in the profile for plasma bulk temperature giving rise to a decreasing trend in the radial direction. This change in bulk plasma temperature triggers further changes in other bulk flow parameters along the radial directions, away from the axis of the flow. In this work, different mathematical models have been proposed for radial correction in the bulk flow parameter profiles within the system size as a simulation for expansion into the vacuum vessel of a magnetic fusion reactor. Symmetry of the radial profiles over a cross-sectional area has been assumed to facilitate ease of computation and analysis.

Mechanical properties and microstructural investigations of TIG welded 40 mm and 60 mm thick SS 316L samples for fusion reactor vacuum vessel applications

The development of advanced fusion reactors like DEMO will have various challenges in materials and fabrication. The vacuum vessel is important part of the fusion reactor. The double walled design for vacuum vessel with thicker stainless steel material (40–60mm) has been proposed in the advanced fusion reactors like ITER. Different welding techniques will have to be used for such vacuum vessel development. The required mechanical, structural and other properties of stainless steels have to be maintained in these joining processes of components of various shapes and sizes in the form of plates, ribs, shells, etc. The present paper reports characterization of welding joints of SS316L plates with higher thicknesses like 40mm and 60mm, prepared using multi-pass Tungsten Inert Gas (TIG) welding process. The weld quality has been evaluated with non-destructive tests by X-ray radiography and ultrasonic methods. The mechanical properties like tensile, bend tests, Vickers hardness and impact fracture tests have been carried out for the weld samples. Tensile property test results indicate sound weld joints with efficiencies over 100%. Hardening was observed in the weld zone in non-uniform manner. Macro and microstructure studies have been carried out for Base Metal (BM), Heat Affected Zone (HAZ) and Weld Zone (WZ). Scanning Electron Microscopy (SEM) analysis carried out for the impact fractured specimens show ductile fracture. The microstructural study and ferrite number data indicate the presence of high content of delta ferrite in the weld zone as compared to the delta ferrite in base metal.

Thick SS316 materials TIG welding development activities towards advanced fusion reactor vacuum vessel applications

Advanced fusion reactors like ITER and up coming Indian DEMO devices are having challenges in terms of their materials design and fabrication procedures. The operation of these devices is having various loads like structural, thermo-mechanical and neutron irradiation effects on major systems like vacuum vessel, divertor, magnets and blanket modules. The concept of double wall vacuum vessel (VV) is proposed in view of protecting of major reactor subsystems like super conducting magnets, diagnostic systems and other critical components from high energy 14 MeV neutrons generated from fusion plasma produced by D-T reactions. The double walled vacuum vessel is used in combination with pressurized water circulation and some special grade borated steel blocks to shield these high energy neutrons effectively. The fabrication of sub components in VV are mainly used with high thickness SS materials in range of 20 mm- 60 mm of various grades based on the required protocols. The structural components of double wall vacuum vessel uses various parts like shields, ribs, shells and diagnostic vacuum ports. These components are to be developed with various welding techniques like TIG welding, Narrow gap TIG welding, Laser welding, Hybrid TIG laser welding, Electron beam welding based on requirement. In the present paper the samples of 20 mm and 40 mm thick SS 316 materials are developed with TIG welding process and their mechanical properties characterization with Tensile, Bend tests and Impact tests are carried out. In addition Vickers hardness tests and microstructural properties of Base metal, Heat Affected Zone (HAZ) and Weld Zone are done. TIG welding application with high thick SS materials in connection with vacuum vessel requirements and involved criticalities towards welding process are highlighted.

A preliminary assessment of beryllium dust oxidation during a wet bypass accident in a fusion reactor

A beryllium dust oxidation model has been developed at the Idaho National Laboratory (INL) by the Fusion Safety Program (FSP) for the MELCOR safety computer code. The purpose of this model is to investigate hydrogen production from beryllium dust layers on hot surfaces inside a fusion reactor vacuum vessel (VV) during in-vessel loss-of-cooling accidents (LOCAs). This beryllium dust oxidation model accounts for the diffusion of steam into a beryllium dust layer, the oxidation of the dust particles inside this layer based on the beryllium–steam oxidation equations developed at the INL, and the effective thermal conductivity of this beryllium dust layer. This paper details this oxidation model and presents the results of the application of this model to a wet bypass accident scenario in the ITER device.

High power Nd:YAG laser welding in manufacturing of vacuum vessel of fusion reactor

Laser welding has shown many advantages over traditional welding methods in numerous applications. The advantages are mainly based on very precise and powerful heat source of laser light, which change the phenomena of welding process when compared with traditional welding methods. According to the phenomena of the laser welding, penetration is deeper and thus welding speed is higher. Because of the precise power source and high-welding speed, the heat input to the workpiece is small and distortions are reduced. Also, the shape of laser weld is less critical for distortions than traditional welds. For welding thick sections, the usability of lasers is not so practical than with thin sheets, because with power levels of present Nd:YAG lasers depth of penetration is limited up to about 10 mm by single-pass welding. One way to overcome this limitation is to use multi-pass laser welding, in which narrow gap and filler wire is applied. By this process, thick sections can be welded with smaller heat input and then smaller distortions and the process seems to be very effective comparing “traditional” welding methods, not only according to the narrower gap. Another way to increase penetration and fill the groove is by using the so-called hybrid process, in which laser and GMAW (gas metal arc welding) are combined. In this paper, 20-mm thick austenitic stainless steel was welded using narrow gap configuration with a multi-pass technique. Two welding procedures were used: Nd:YAG laser welding with filler wire and with addition of GMAW, the hybrid process. In the welding experiments, it was noticed that both processes are feasible for welding thicker sections with good quality and with minimal distortions. Thus, these processes should be considered when the evaluation of the welding process is done for joining vacuum vessel sectors of ITER.

Numerical Analysis on Ingress of Coolant Event in Vacuum Vessel of Fusion Reactor Using Modified TRAC-BF1

The semi three-dimensional numerical analysis model of the FDR-ITER to simulate the in-vessel LOCA or the ICE was constructed using the modified TRAC-BF1 code in which the vacuum vessel, the pressure suppression tank and the relief pipe header are modeled using one VESSEL component. Analytical results obtained from the modified TRAC-BF1 code were compared with those from the MELCOR code concerning pressure in the vacuum vessel when a cooling pipe of 0.6 m2 flow area breaks in it. The mass flow rate of the injected water into the vacuum vessel and the initial wall temperature in the modified TRAC-BF1 input data were the same as those calculated in the MELCOR analysis. The maximum pressure in the vacuum vessel obtained from the modified TRAC-BF1 code is 10% higher than that from the MELCOR code, but it is still below the design pressure 0.5 MPa of the FDR-ITER vacuum vessel. The semi three-dimensional analysis using the modified TRAC-BF1 obtained that the maximum delay in opening time among the four rupture-disks is within 3 ms. The maximum pressure in the vacuum vessel does not exceed the design pressure, even if one of rupture-disks is not opened.

Numerical Analysis on Ingress of Coolant Event in Vacuum Vessel of Fusion Reactor Using Modified TRAC-BF1.

The semi three-dimensional numerical analysis model of the FDR-ITER to simulate the in-vessel LOCA or the ICE was constructed using the modified TRAC-BF1 code in which the vacuum vessel, the pressure suppression tank and the relief pipe header are modeled using one VESSEL component. Analytical results obtained from the modified TRAC-BF1 code were compared with those from the MELCOR code concerning pressure in the vacuum vessel when a cooling pipe of 0.6 m2 flow area breaks in it. The mass flow rate of the injected water into the vacuum vessel and the initial wall temperature in the modified TRAC-BF1 input data were the same as those calculated in the MELCOR analysis. The maximum pressure in the vacuum vessel obtained from the modified TRAC-BF1 code is 10% higher than that from the MELCOR code, but it is still below the design pressure 0.5 MPa of the FDR-ITER vacuum vessel. The semi three-dimensional analysis using the modified TRAC-BF1 obtained that the maximum delay in opening time among the four rupture-disks is within 3 ms. The maximum pressure in the vacuum vessel does not exceed the design pressure, even if one of rupture-disks is not opened.

核融合装置真空容器用板厚貫通電子ビーム溶接継手の強度

核融合装置真空容器用板厚貫通電子ビーム溶接継手の強度

Fusion reactor vacuum vessel cooldown

Abstract The paper discusses a new approach to the International Thermonuclear Experimental Reactor vacuum vessel (W) cooldown. The approach is based on equalizing temperatures of the inside and outside VV walls and securing approximately equal coolant flow rates through W components under normal operating conditions and in emergency situations. It is based on the coolant flow rate redistribution in clearances between the walls and the in-vessel steel/water shielding plates as well on the application of a two-circuit VV cooldown system with the use of an ebullience pipe.

810 核融合炉真空容器溶接部の健全性評価法

810 核融合炉真空容器溶接部の健全性評価法

Numerical Simulation of Two-Phase Flow Behavior in a Fusion Reactor during an Ingress-of-coolant Event

An analytical study was performed to understand the physical phenomena after an ingress-of-coolant event (ICE) in a fusion reactor. A simulation code was developed to identify two-phase flow behavior in a fusion reactor vacuum vessel (VV). It consisted of mass, momentum, and energy equations of the liquid and gas. Numerical simulations were carried out to obtain quantitative predictions. Distributions of pressure, temperature, velocity and void fraction in the VV were obtained and an impingement-jet behavior of water under vacuum conditions were clarified numerically.

Temperature distributions in a Tokamak vacuum vessel of fusion reactor after the loss-of-vacuum events occurred

If a loss-of-vacuum event (LOVA) occurred in a fusion reactor, buoyancy-driven exchange flows would take place at breaches of a vacuum vessel (VV) due to the temperature difference between the inside and outside of the VV. The exchange flows may bring mixtures of activated materials and tritium in the VV to the outside through the breaches, and remove decay heat from the plasma-facing components of the VV. Therefore, the LOVA experiments were carried out under the conditions that one or two breaches were opened and that the VV was heated to a maximum 200°C, using a small-scaled LOVA experimental apparatus. Air and helium gas were provided as working fluids. Fluid and wall temperature distributions in the VV were measured and the flow patterns in the VV were estimated from these temperature distributions. It was found that: (1) the exchange mass in the VV depended on the breach positions; (2) the exchange flow at the single breach case became a counter-current flow when the breach was at the roof of the VV and a stratified flow when it was at the side wall; (3) and that at the double breach case, a one-way flow between two breaches was formed.

Exchange Flow Characteristics in a Tokamak Vacuum Vessel of Fusion Reactor Under the Loss-of-Vacuum Conditions

When a Tokamak vacuum vessel of fusion reactor is broken, buoyancy-driven exchange flows will take place through breaches after the inside pressure of the vacuum vessel (VV) becomes equal to the outside pressure. The exchange flow may bring a mixture of activated dusts and tritium from the inside of the VV to the outside through the breaches. Moreover, the exchange flow may remove decay heat from the plasma-facing components. A preliminary LOVA (Loss Of VAcuum event) apparatus was constructed to investigate quantitative heat transfer characteristics of the exchange flows through the breaches under the LOVA conditions. The results of this study, the relationship between Froude numbers and breach locations in the VV was determined and empirical correlations for the average Froude numbers were derived.