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Radiation shielding and tritium breeding performances of the helical DEMO reactor FFHR-d1 have been investigated for the present proposed reactor component configuration. Since the core plasma position shifts to inboard side of the torus, the total thickness of the inboard breeding blanket and radiation shield of FFHR-d1 is limited to ∼70 cm. To simulate the geometric features of the helical reactor, three-dimensional neutronics calculation model consisted of ∼4,000 cells have been prepared for the neutron and gamma-ray transport calculations using the MCNP code. It has been confirmed that the present radiation shield configuration with WC (tungsten carbide) and FS (ferritic steel) + B4C layers would provide sufficient shielding performance for the helical coils. The tritium breeding ratio (TBR) of 1.08 has been obtained with a Flibe+Be/FS breeding blanket for the present component configuration of FFHR-d1. c

Conceptual design activity for the LHD-type helical DEMO reactor FFHR-d1 has been conducted at the National Institute for Fusion Science under the Fusion Engineering Research Project since FY2010. In the first step of the conceptual design process, design window analysis was conducted using the system design code HELIOSCOPE by the “Design Integration Task Group”. On the basis of a parametric scan with the core plasma design based on the DPE (Direct Profile Extrapolation) method, a design point having a major radius of 15.6 m and averaged magnetic field strength at the helical coil winding center of 4.7 T was selected as a candidate. The validity of the design was confirmed through the analysis by the related task groups (in-vessel component, blanket, and superconducting magnet).

The plasma diagnostics required for a heliotron-type DEMO reactor are discussed in terms of real-time burn control and safe operation of the machine. The minimum diagnostic set having the smallest footprint are essential in DEMO. Neutron transport calculation suggests that the diagnostic components used in existing experiments will deteriorate immediately in a DEMO reactor hall if they are not protected by a neutron shield. Neutron energy spectrometry is a promising diagnostic that is expected to play an important role in diagnosing DEMO plasmas, providing a fusion energy output, fuel ion temperature, ratio of deuteron density nD to triton density nT, and velocity distribution of confined α particles.

Ion-beam induced luminescence of sintered Er2O3 samples irradiated by Ar+ ion-beams was measured in a visible range. In this experiment, three emission bands were observed at 500-520, 540-570, and 640-690nm. The measured luminescence band at 640-690nm is resolved into Lorentzian Stark component having a ? 1012 Hz width in frequency. Center wavelengths of the Stark components agree with those of intra-4f transitions of Er3+ (4f11) ions situated at C2 symmetry cation sites in pure Er2O3. However, resonance broadening due to nearby Er3+ in the crystal accounts only 1% of the total width. Depopulation of the crystalline oxide in irradiated regions is inferred from decreasing intensity of the emission band at 640-690nm during continuous irradiation. The emission bands at 500-520 and 540-570nm still remained in heavily damaged samples look similar with those observed with a metallic Er target.

Erbium oxide (Er2O3) was shown to be a high potential candidate for tritium permeation barrier and electrical insulator coating for advanced breeding blanket systems such as liquid Li, Li-Pb or molten-salt blankets. Recently, we succeeded to form Er2O3 coating layer on large interior surface area of metal pipe using Metal Organic Chemical Vapor Deposition (MOCVD) process. In this paper, we investigated the microstructure of Er2O3 coating layer on stainless steel 316 (SUS 316) plate before and after heat treatments with hydrogen or argon gases. From the results of TEM observations, we confirmed that Er2O3 coating layer with 700 nm thickness was formed on the SUS 316 plate and this layer was identified to poly-crystal phase because the diffraction fleck which was arranged like a ring was observed in the selected electron diffraction pattern. No macroscopic defects such as crack and peeling in Er2O3 coating layer were observed before and after thermal cycling test. The change of microstructure of the Er2O3 coating layer on before and after heat cycling test was reported.

The electroplating of Er metal on the reduced activation ferritic martensitic steel, JLF-1 (Fe-9Cr-2W-0.1C), in a molten salt was studied. The specimen was immersed in the molten ErCl3 doped LiCl-KCl electrolyte. The electroplating was carried out by a constant potential electrolysis method and a pulsed current electrolysis method. It was found that the Er metal was deposited on the specimen surface due to the electrochemical reaction.

Ion-beam induced luminescence of sintered Er2O3 samples irradiated by Ar ion-beams was measured in a visible range. In this experiment, three emission bands were observed at 500-520, 540-570, and 640-690 nm. The measured luminescence band at 640-690 nm is resolved into Lorentzian Stark component having a ∼ 1012 Hz width in frequency. Center wavelengths of the Stark components agree with those of intra-4f transitions of Er3+ (4f11) ions situated at C2 symmetry cation sites in pure Er2O3. However, resonance broadening due to nearby Er3+ in the crystal accounts only 1% of the total width. Depopulation of the crystalline oxide in irradiated regions is inferred from decreasing intensity of the emission band at 640-690 nm during continuous irradiation. The emission bands at 500-520 and 540-570 nm still remained in heavily damaged samples look similar with those observed with a metallic Er target.

According to the achievements in the Large Helical Device (LHD) experiments, a design of a DEMO reactor with a LHD-type heliotron system is foreseeable. On the other hand, a DEMO is the next step reactor and high reliability and feasibility are demanded in its design. In this study, a robust design window, i.e., the design window that is not sensitive to a change in uncertain physics parameters, was surveyed through parametric scans using a system design code. It was found that a difference in main design parameters (major radius, magnetic field strength, fusion output) gives only a small change in a dependence of physics requirements on the physics conditions. Therefore, it is important to find the design window with a lower requirement on the confinement improvement to assure the design robustness. In this respect, a reduction in the minimum inboard blanket space, one of the key parameters in a LHD-type heliotron reactor design, can effectively expand the design window and contributes to the design robustness. An acceptance of higher neutron wall load and an achievement of further high confinement improvement are also expected to make both a DEMO and a commercial reactor to be more feasible and economically attractive.

The development of functional layers such as a tritium permeation barrier and an anti-corrosion layer is the essential technology for the development of a molten salt type self cooled fusion blanket. In the present study, the characteristics of a nitriding treatment on a reduced activation ferritic steel, JLF-1 (Fe-9Cr-2W-0.1C) as the functional layer were investigated. The steel surface was nitrided by an ion nitriding treatment or a radical nitriding treatment. The nitridation characteristic of the steel surface was made clear based on the thermodynamic stability. The thermal diffusivity, the hydrogen permeability and the chemical stability in the molten salt Flinak were investigated. The results indicated that the nitriding treatment can improve the compatibility in the Flinak without the decrease of the thermal diffusivity, though there was little improvement as the hydrogen permeation barrier.

We developed a lost alpha detection system to use in burning plasma experiments. The scintillators of Ag:ZnS and polycrystalline Ce:YAG were designed for a high-temperature environment, and the optical transmission line was designed to transmit from the scintillator to the port plug. The required optical components of lenses and mirrors were irradiated using the fission reactor with the initial result that there was no clear change after the irradiation with a neutron flux of 9.6×10(17) nm(-2) s(-1) for 48 h. We propose a diagnostic of alpha particle loss, so-called alpha particle induced gamma ray spectroscopy. The initial laboratory test has been carried out by the use of the Ce doped Lu(2)SiO(5) scintillator detector and an Am-Be source to detect the 4.44 MeV high energy gamma ray due to the (9)Be(α,nγ)(12)C reaction.

Neutronics investigations have been conducted in the design activity of the helical-type reactor Force Free Helical Reactor (FFHR2) adopting Flibe-cooled and Li-cooled advanced liquid blanket systems. In this study, comprehensive investigations and geometry modifications related to the tritium breeding ratios (TBRs), neutron shielding performance and neutron wall loading on the first walls in FFHR2 have been performed by improving the three-dimensional (3D) neutronics calculation system developed for non-axisymmetric helical designs. The total TBRs obtained after modifying the blanket dimensions indicated that all the advanced blanket systems proposed for FFHR2 would achieve adequate tritium self-sufficiency by dimension adjustment and optimization of structures in the breeder layers. However, it appeared that the most important neutronics issue in the present helical blanket configuration was suppression of neutron streaming through the divertor pumping areas and reflection from support structures for protection of poloidal and helical coils. Evaluation of neutron wall loading on the first walls indicated that the peaking factor would be moderated as low as 1.2 by the toroidal and helical effect of the helical-shaped plasma distribution in the helical reactor.

Neutronics analyses for Li/V-alloy and Flibe/V-alloy liquid blankets with and without external beryllium were performed for the FFHR2 design in order to assess the tritium breeding ratios (TBRs) and neutron shielding performances. Beryllium multiplier significantly improved the TBRs for both the Li/V-alloy and Flibe/V-alloy blankets. The shielding performance of the Li/V-alloy blanket with Be was greatly improved because the adequate TBRs can be obtained with the thinner breeding region than in the Li/V-alloy blanket without Be and the thickness of the shielding region was increased. On the other hard, the shielding performance of the Flibe/V-alloy blankets with and without external Be was comparable. It was shown that the Li/V-alloy and Flibe/V-alloy liquid blankets with and without solid Be satisfied the requirement for TBRs and shielding for the superconductor magnet of FFHR2. The activation of MHD coating of Er2O3 for the Li/V-alloy blankets and activation performance of the Flibe/V-alloy blankets were also investigated for the cases with and without external Be. The MHD coating of Er2O3 in the Li/V-alloy blankets introduced long-lived activation products. The activation of the Flibe/V-alloy blanket with external Be was comparable to that without external Be.

Several ceramic detectors were made by use of the insulation layer formed on two types of substrate, i.e. aluminum and silicon. Each detector was irradiated with alpha-rays from an Am-241 source and the electric charge induced in the detector was measured in the temperature range from room temperature up to 450 K. The alpha-ray detection signals were well observed with an oscilloscope at the properly high bias-voltage only for very short time from several seconds to several tens of seconds before the start of the sweeping insulation breakdown. Though this type of the simple detector made of a thin ceramic layer can be hardly used for the energy analysis, it might be effectively applicable to the measurement of the flux of alpha-particles at high temperature.

Synthetic diamondradiation detectors made of ultrahigh-purity type IIa diamond crystals were developed. The diamond crystals, which were grown by high-pressure and high-temperature synthesis, contained less nitrogen impurity than 0.1 ppm, i.e., 1/10 of conventional type IIa diamond crystals. Since the ultrahigh-purity type IIa diamond crystal was a p-type semiconductor due to a trace impurity of boron, a structure consisting of Schottky and ohmic contacts was adopted for the detectors to suppress an increase in leakage current. For the same purpose, a metal–insulator–semiconductor structure using a chemical vapor deposition diamond insulating layer was adopted for one of the detectors. Plural peaks were observed in the 5.486 MeV α energy spectra obtained by the detectors; motion of holes produced the main part of output pulses from the detectors on these measurements. One of the peaks in each spectrum was hardly influenced by light irradiation, even ultraviolet light of 370 nm (3.4 eV), compared with a peak obtained by the conventional type IIa diamondradiation detector. This experimental result indicated that there was a superior part in the crystal where deep energy levels did not exist so much. Although there was no direct evidence, influence of a distribution of the boron impurity in the crystal was expected. On the other hand, electron trapping severely occurred and resulted in loss in charge collection; an effect of the reduction in the nitrogen impurity was not confirmed on the behavior of electrons.

Ionospheric disturbances caused by the Urakawa-Oki earthquake at 0232 UT on 21 March 1982 have been detected by a network of HF-Doppler sounders in central Japan. The HF-Doppler data, together with the seismic data, have been used to formulate a mechanism whereby ionospheric disturbances are produced by an event of relatively small epicentral distance. Comparison of the dynamic spectra of these data has revealed experimentally that the atmosphere acts as a low-pass filter for the upward-propagating acoustic waves. The cut-off periods of this filter are estimated by applying a digital filter technique to the up-down component of the seismograms and are found to be 10 s from the ground up to 156 km and 20 s from 156–195 km. Considering the transfer function of the atmosphere derived from the theory of Pitteway and Hines, the observed result does not contradict the prediction that the atmospheric filter mechanism is mainly attributable to viscosity.

A series of irradiation experiments were performed using Fusion Neutronics Source (FNS) at JAEA for the investigation of activation of materials relevant to Lithium/vanadium-alloy and Flibe/vanadium-alloy blankets. The specimens of V-4Cr-4Ti, Er and Teflon in 10 mmx10 mmx0.03-0.1 mm were prepared for studying the activation of V-alloy structure, MHD coating of Er 2 O 3 , and F in molten salt Flibe, respectively. Be, Li and Li/Be mock-ups were assembled with Be and solid Li blocks in addition to the assembly for direct D-T neutron irradiation to examine the dependence of the activation on neutron spectrum. The neutron spectra in all irradiation locations were calculated using MCNP code and JENDL-3.3 file. The activities of the specimens induced in various neutron fields were measured with a high purity Ge detector (HP-Ge). Experimental analyses were carried out using FISPACT-2001 codes with both EAF-2001 file and FENDL/A-2.0 & FENDL/D-2.0 libraries. The typical calculation/experiment(C/E) values lay in the range of 0.8-1.2. Coarse group treat for (n, y) reactions, especially in resonance range, could result in overestimation. Use of continuous cross section improves consistency of the calculation with the experiment. However, accurate estimate of spectra is necessary when the flux changes largely with energy around the threshold or the resonance peak.

Some test materials (i.e. Fe, Cr, Y and JLF-1 steel) were immersed to liquid metal lead (Pb) mainly at 773 K as the working electrode of electrochemical impedance spectroscopy (EIS). Some oxide layers formed on the electrodes in liquid Pb were analyzed by EIS. The impedance response was summarized as semicircular Nyquist plot, and the electrical properties and the thickness of the oxide layers were evaluated in non-destructive manner. Large impedance due to the formation of Y oxide formed in liquid Pb was detected by EIS, though impedance of Fe oxide and Cr oxide could not be detected due to their small electro resistance. The time constant of the oxide layers was evaluated from the impedance information, and this value identified the types of oxides. The change of the time constant with the immersion time indicated the change of the electrical properties determined by the chemical composition and the crystal structure. The thickness of the oxide layer estimated by EIS agreed well with that evaluated by metallurgical analysis. The growth of Y oxide layer in the liquid Pb was successfully detected by EIS in non-destructive manner.

The experimental studies on fabrication methods of a lithium lead alloy (Pb-Li) and desorption of non-metal impurities dissolved in the alloys were carried out. The alloys having various Li concentrations were fabricated from small metal grains of Pb and Li. The desorption behavior of gases dissoved in Pb, Pb-Bi and Pb-Li was investigated by the temperature programmed desorption (TPD) analysis. Pb and Pb-Bi contained H2O and CO2, and these chemical compounds were desorbed from the alloys below 700K. Desorption of H2 from Pb-17Li was detected. These behaviors were based on their thermodynamic stability in the alloys. It was found that the non-metal impurities in the alloys could be removed by the TPD method.

To examine the accuracy in the neutronics calculations for the Li/V-alloy blanket system without Be neutron multiplier, a fusion neutronics experiment on a Li/V-alloy assembly has been performed wi...

Combination of liquid lithium with Reduced Activation Feritic/Martensitic Steel (RAFM) is one of the options for Test Blanket Module (TBM) in early ITER period and early DEMO blanket, as well as an...