Study on turbulent heat transfer mechanism inside high-speed lithium jet irradiated by ion beam for fusion neutron sources

Liquid lithium (Li) jet is planned as a beam target in fusion neutron sources developed in Japan and EU. We have been studying the hydrodynamic characteristics of the Li jet experimentally and numerically. For the safety and the efficiency of fusion neutron sources, it is necessary to understand the heat transfer inside the Li target irradiated by ion beams. In this paper, in order to evaluate the heat transfer under the turbulent flow with complex vortex structure inside the Li jet, 3-dimensional simulation of it with beam irradiation is conducted using LES. As the first step of this study, the Li jet is modeled as single-phase for reducing the computational load, in which the Li surface is treated as the free-slip boundary condition. Simulation model is large-scale with over thirty million meshes for resolving the detailed vortex structure. In this simulation, it was found that the temperature peak was disturbed by wall turbulence near the bottom wall of the flow channel

Interaction between surface behavior and inner flow pattern of liquid Li jet for fusion neutron sources

Liquid lithium (Li) jet is planned as a beam target in fusion neutron sources (FNSs), such as IFMIF in Japan and EU, A-FNS in Japan and IFMIF-DONES in EU. For the safety and the efficiency of such FNSs, it is desirable to keep the high-speed Li jet stable. In addition to many experimental researches, numerical approaches using CFD simulation have been also required to evaluate the detailed flow pattern inner the Li jet because of the opacity. In our previous simulation, it was found that the vortex structure under the free surface of the Li jet had the strong influence on the surface fluctuation using LES simulation. In this study, for evaluating the interaction between the Li surface behavior and the flow pattern inner the Li jet, two simulations are conducted: one is the LES simulation considering wall roughness, and another one is the RANS simulation using full-scale model with the nozzle and the Li jet. The influence of wall roughness on the vortex structure becomes an issue in long-term operation of actual FNSs, and the influence of the secondary flow generated due to the side wall on the surface shape is evaluated in the latter simulation

Measurement of transient flow characteristics of target flow in water experiment for IFMIF

International Fusion Material Irradiation Facility (IFMIF) is the facility generating the high flux and high energy neutrons to develop fusion reactor materials. In IFMIF, high-speed liquid lithium (Li) jet is used as the target irradiated by deuteron beams. Since the Li jet must flow with high velocity for heat removal, it is important to research on the Li flow characteristics. These researches have been aimed toward the steady-state Li flow characteristics. On the other hand, in the actual IFMIF, it is also necessary to clarify transient flow characteristics at start and stop of the system for the operation. In this study, water experiment to obtain them at start and stop is thus conducted. Water can be substituted for liquid Li as the target, because the kinematic viscosity of the Li at operation temperature in IFMIF is nearly equal to that of water at normal temperature and pressure. Flow patterns of the water jet at test section which consists of a two-staged contraction nozzle, a vertical concave flow channel are observed by laser probe method and high-speed video camera. As a result, the flow pattern at start and stop was successfully observed. The flow at stop became stable by venting gas

Free-Surface Characteristics of a Liquid Li Wall Jet

In this study, the free-surface characteristics of a liquid Li wall jet for the Li target of the International Fusion Materials Irradiation Facility (IFMIF) are comprehensively reviewed. In developing the IFMIF Li target, a scientific understanding of the free-surface wave characteristics and the development of diagnostic tools to measure these characteristics were critical issues. The same issues must be faced in other liquid metal applications in fusion engineering, such as liquid first walls or liquid diverters. Thus far, diagnostic tools and methods to measure all of the characteristics of waves (i.e., wavelength, wave period, wave speed (free-surface speed), wave height (amplitude)), and average jet thickness have been developed, and the probability distributions applicable to these wave parameters, as well as their statistical characteristic values, have been determined, validating the stability of the IFMIF Li target. Our findings, both the wave characteristics and the diagnostic tools, can be appliedto not only the IFMIF Li target but also innovative liquid metal diverters or first walls in fusion engineering

Verification of accuracy of contact-probe distance meter for lithium target of fusion neutron source

An accelerator based intense neutron sources such as the IFMIF, A-FNS and DONES produce neutron flux by a stripping reaction between lithium (Li) and deuteron for testing various materials for fusion reactor. In these fusion neutron sources, a liquid Li free-surface jet is applied as the liquid Li target. For the development of the Li target system, the variation in the thickness of the Li jet was measured using the Li loop of Osaka University. At the Osaka Univ., a lot of knowledge about the surface fluctuation of the Li jet had been obtained by using the electro-contact type distance meter (referred to as the probe apparatus herein). Besides, for the stable and safety operation of the facility, the probe apparatus is planned to be used as a safety interlock system for beam irradiation in actual intense neutron source because of its simple structure. Therefore, it is desirable to verify its accuracy. Especially, it is expected that false detection and undetected waves, which is particular to the contact-type apparatus, could cause errors. Then in this study, the measurement using non-contact type distance meter using optical comb (referred to as the laser probe herein) was conducted, and then the error of the results of the probe apparatus is evaluated by comparing results