Katsusuke Shimizu

Laser‐prearc railgun: Development for the application to a fuel pellet injector of a nuclear fusion reactor

The laser‐prearc railgun, that utilizes the phenomenon of laser‐induced arc formation, was constructed and tested with plastic pellet projectiles. We envision our railgun as especially well suited as a solid hydrogen pellet injector for magnetic confinement fusion. The system consisted of a gas gun for preacceleration of a pellet and a railgun for its primary acceleration. A Q‐switched ruby laser was used to induce electrical breakdown of propellant helium gas behind a dielectric pellet in the railgun. The present railgun was shown to accelerate a plastic pellet up to a velocity of 2.4 km/s.

Latest liquid lithium target design during the key element technology phase in the international fusion materials irradiation facility (IFMIF)

Abstract International Fusion Materials Irradiation Facility (IFMIF), being jointly developed by EU, JA, RF and US, is a deuteron–lithium (Li) stripping reaction neutron source for fusion materials testing. In 2002, a 3 year Key Element technology Phase (KEP) to reduce the key technology risk factors was completed. A liquid Li target has been designed to produce intense high energy neutrons (2 MW/m 2 ) up to 50 dpa/year by 10 MW of deuterium beam deposition which corresponds to an ultra high heat load of 1 GW/m 2 . This paper describes the latest design of the liquid Li target system reflecting the KEP results and future prospects.

Development of conductively cooled first wall armor and actively cooled divertor structure for ITER/FER

Abstract Based on the design requirements for the plasma facing components in ITER/FER, we have performed design studies on the conductively cooled first wall armor and the divertor plate with sliding supports. The full-scale armor tiles were fabricated for heat load tests, and good thermal performances were obtained in heat load tests of 0.2–0.4 MW/m 2 . It is shown by the thermomechanical analysis on the divertor plate that thermal stresses and bending deformation are reduced significantly by using the sliding supports. The divertor test module with the sliding supports has been fabricated to investigate its fabricability and to verify the functions of the sliding supports during a high heat load of about 10 MW/m 2 .

Structural evaluation of a compact, semi-closed W-shaped divertor system for JT-60U

Abstract A compact, semi-closed W-shaped divertor system has been designed, fabricated and installed in the JT-60U to replace the open divertor system. The new system consists of inclined divertors, a dome and baffles. To meet the structural requirements, a segmented structure with an electrically insulated flexible gas seal was applied. Using FEM codes, the system’s structural integrity was confirmed for the plasma disruptions by electromagnetic and structural analyses, which take into account the effect of halo currents. Substantial reduction of induced electromagnetic forces is attained in the divertor system due to the electrical insulation used for the gas seal structure. In addition, because of its segmented structure, the induced electromagnetic forces on each component unit are found to be limited. The maximum stress intensities and their ranges are obtained within allowable values. Thermal stress arising from the temperature difference between the divertor system and the vacuum vessel during the baking operation is also satisfactory. Furthermore, thermal and thermal stress analyses showed that the plasma facing components have sufficient structural integrity.

ITER magnet and structure assembly plan

The International Thermonuclear Experimental Reactor (ITER) is the largest tokamak that has ever been planned. The assembly of the ITER machine presents several unique problems for handling, alignment and bracing of the superconducting magnets and structure components, in particular the toroidal field (TF) coil with the corresponding vacuum vessel (VV) sector (1,200 tonnes), and the central solenoid (CS) with the bucking cylinder (BC) assembly (1,350 tonnes). Accurate positioning of the toroidal field coils relative to one another, and relative to the central solenoid will be required, to achieve the design stresses in the magnets during cooldown, and machine operation. Special tooling will be used to limit component distortion during installation, shorten the schedule, and reduce the cost. Assembly issues and features of handling, positioning, and immobilizing of the superconducting coils and structure components for the ITER are discussed.

Environmentally-Friendly HTGR: MHR-50/100—Concept and Characteristics

A business plan and a new concept of the Mitsubishi small-sized High temperature gas-cooled modular Reactors (MHR-50/100) had been developed as reported in a paper at the HTR-2010 conference in Prague. The present paper reports the results of ensuing conceptual design study including updated market researches, improved safety features of the plant, and the plant dynamics analysis. Market researches on Japan, the USA, Southeast Asia and the Middle East have been updated applying the latest energy outlook data. The result shows that the potential market share for the type of HTGR (high temperature gas reactor) reactors is expected to be 10–20% in new construction of heat source plants in those market areas. A financial analysis made based on the results of the updated market research and the plant cost evaluations indicates that the feasibility of an HTGR business potentially exists. Concerning about the conceptual design, as main themes of the study, a plant design, safety design and plant dynamics have been carried out. The MHR-50/100 high safety characteristics have been confirmed based on the results of the following studies as reported in the present paper: (1) An investigation of a safety scenario during occurrence of a Total Black Out event; (2) An analysis of the reactor decay heat removal via a natural circulation. Lastly, the control methods for the reactor and associated steam cycle system for the MHR-50 have been studied. The results show that the reactor power changes can be effectively achieved by controlling the primary system helium flow rate. The ASURA code developed by MHI is used for simulation of such typical plant transients as 10% step load reduction and full load rejection. The results confirm the easy operability and controllability of the plant.Copyright

Numerical evaluation of experimental models to investigate the dynamic behavior of the ITER tokamak assembly

The most recent assessment method to evaluate the dynamic behavior of the International Thermonuclear Experimental Reactor (ITER) tokamak assembly is outlined. Three experimental models, including a 1/5.8-scale tokamak model, have been considered to validate the numerical analysis methods for dynamic events, particularly seismic ones. The experimental model has been evaluated by numerical calculations and the results are presented. In the calculations, equivalent linearization has been applied for the non-linear characteristics of the support flange connection, caused by the effects of the bolt-fastening and the friction between the flanges. The detailed connecting conditions for the support flanges have been developed and validated for the analysis. Using the conditions, the eigen-mode analysis has shown that the first and second eigen-mode are horizontal vibration modes with the natural frequency of 39 Hz, while the vertical vibration mode is the fourth mode with the natural frequency of 86 Hz. Dynamic analysis for seismic events has shown the maximum acceleration of approximately twofold larger than that of the applied acceleration, and the maximum stress of 104 MPa found in the flange connecting bolt. These values will be examined comparing with experimental results in order to validate the analysis methods.

Development and design of railgun system to pellet injector

Railgun systems for the application of pellet injectors have been investigated and developed in the experimental stage. One of the main features of these railgun systems is the use of a pulse laser beam to induce the initial plasma armature between rails to be accelerated. This unique feature provides a reduction of the supplied voltage to the breakdown between the rails in order to avoid any unnecessary breakdown between the rails and to reduce the erosion of the rails. The authors present results of experimental and theoretical research and introduce the design study for a repetitive pellet injection systems with an electromagnetic railgun based on the research progress.<<ETX>>

History and Organization of Fusion Research and Development in Japan

This paper discusses nuclear fusion research and development in Japan, which depends on other countries for its energy resources. The author discusses how development of both the basic research and the advanced technology required for nuclear fusion is a challenge that can be met with Japans industrial resources.

DEVELOPMENT OF RAILGUN SYSTEM TO PELLET INJECTION FOR FUSION REACTOR REFUELING

Literature study on over 10-20km/s pellet injector indicates that electromagnetic accelerators are very attractive, especially a railgun system is very promising. So a railgun system has been developed in order to examine the possibility of this system of pellet injection for fusion reactor refueling as a technique of high velocity pellet injection. The system is composed of a light gas gun preaccelerator and a railgun accelerator. The performance tests have proven that the system can accelerate high speed plastic pellets. The maximum pellet velocity obtained in the plastic pellet tests is greater than 1.8km/sec in the case that the preaccelerated pellet velocity is 0.35km/sec. The device is under experimentation to determine the detail conditions for accelerating pellets and obtaining high pellet velocity.