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The current status and the progress of R&D activities for a Fusion DEMO reactor in the QST Rokkasho Fusion Institute is reported. In order to advance the JA DEMO activity, not only Japanese domestic activity but also international collaborations of Broader Approach Activity and ITER related activities are conducted in the QST Rokkasho Fusion Institute. Activities for DEMO design and relevant R&D, design of a fusion neutron source and development of an accelerator, ITER-TBS, tritium handling technology and information technology infrastructures including a supercomputer system and a remote experimentation system are carried out for a Fusion DEMO reactor.

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.

Liquid lithium, a candidate material for the target of International Fusion Material Irradiation Facility (IFMIF), easily contains nitrogen. Nitrogen in liquid lithium should be removed as it accelerates corrosion of tubing materials. Hot trapping by iron-titanium alloys is expected to be a practical method. In order to understand the characteristics of nitrogen trapping with iron-titanium alloys in liquid lithium, nitrogen distribution was observed by Soft X-ray Emission Spectroscopy (SXES). Samples of Fe-5Ti alloys were immersed for 9–256 h in liquid lithium which contains 1000 w-ppm of nitrogen at 823 K and studied by X-ray Powder diffraction and SXES. The results show that nitrogen is trapped mainly in the grain boundaries and on the surfaces of the Fe-5Ti alloys and diffuses in Fe-5Ti much faster than in pure titanium. In addition, it is assumed that the amount of nitrogen trapping by the surface of Fe-5Ti alloys does not depend on the immersion time.

We have established a conceptual design of Advanced Fusion Neutron Source (A-FNS). In order to obtain irradiation data required in qualifying materials of fusion DEMO DT reactor, we newly designed nine test modules (TMs) to be implemented in the A-FNS. The design of the test modules is based on a new distinctive maintenance scheme: ‘horizontal maintenance method integrated with the shielding plug’. By integrating the TMs with the shield plug and transferring those from the test cell to the access cell, we can avoid disconnecting and connecting the huge amounts of the pipes and cables by means of the remote handling inside the test cell. We determined a configuration of the TMs in the test cell so as to achieve the required irradiation data for each of the test modules. The maximum dpa of F82H specimens in the TM for blanket structural material was about 10 dpa/fpy, which was designed to fulfil critical requirement by accumulated irradiation for two years and operation duration for four years with the operation availability of 50%. A-FNS was designed so that the huge amounts of neutrons generated can be utilized for various non-fusion purposes as well as the fusion materials irradiation. We newly designed a module to produce the significant amount of 99Mo for a medical purpose. The module for such a non-fusion purpose can be installed in the test cell with the compatibility of the fusion materials irradiation tests.

In A-FNS, an accelerator-driven fusion-relevant neutron source, a few grams (3.5 g at full power operation) of tritium will be generated every year mainly in lithium target system. Since the generated tritium would migrate out of lithium target system, it is necessary to estimate the tritium migration in and out of the lithium target system for the design of detritiation systems for A-FNS, and therefore, a preliminary estimation is performed in the present study. As the results, it is found that almost all of the generated tritium in lithium target system would be trapped in impurity removal system, while less than 0.5% of that would migrate out. It is also indicated that the amount of tritium that would migrate out of lithium target system would be able to process with the existing techniques so far.

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.

In order to assess radiation damage of a fusion material before a decision of Japanese fusion DEMO reactor construction, we have been designing an intense d-Li neutron source facility, Advanced Fusion Neutron Source (A-FNS) in Japan. A-FNS will be constructed before 2025. The main purpose of A_FNS is to acquire radiation damage data of the fusion material under fusion-like neutron irradiation testing. One of the characteristics of A-FNS is that large amounts of high energy neutrons (> MeV) are produced with an expected intensity around 6.8 x 10^16 n/s. In this study, we propose a neutron measurement system that is configured with multiple threshold reaction activation foils that are sensitive to high energy neutrons. The need to measure the cross-section data for the threshold reactions is also discussed.

Liquid lithium, a candidate material for the target of International Fusion Material Irradiation Facility (IFMIF), easily contains nitrogen. Nitrogen in liquid lithium should be removed as it accelerates corrosion of tubing materials. Hot trapping by iron-titanium alloys is expected to be a practical method. In order to understand the characteristics of nitrogen trapping with iron-titanium alloys in liquid lithium, nitrogen distribution was observed by Soft X-ray Emission Spectroscopy (SXES). Samples of Fe-5Ti alloys were immersed for 9–256 hours in liquid lithium which contains 1000 w-ppm of nitrogen at 823 K and studied by X-ray Powder diffraction and SXES. The results show that nitrogen is trapped mainly in the grain boundaries and on the surfaces of the Fe-5Ti alloys and diffuses in Fe-5Ti much faster than in pure titanium. In addition, it is thought that the amount of nitrogen trapping by the surface of the alloys does not depend on the immersion time., 31st Symposium on Fusion Technology (SOFT2020)

In A-FNS, an accelerator-driven fusion-relevant neutron source, a few grams (3.5 g at full power operation) of tritium will be generated every year mainly in lithium target system. Since the generated tritium would migrate out of lithium target system, it is necessary to estimate the tritium migration in and out of the lithium target system for the design of detritiation systems for A-FNS, and therefore, a preliminary estimation is performed in the present study. As the results, it is found that almost all of the generated tritium in lithium target system would be trapped in impurity removal system, while less than 0.5% of that would migrate out. It is also indicated that the amount of tritium that would migrate out of lithium target system would be able to process with the existing techniques so far., Technology of Fusion Energy (TOFE2020)

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.