Tatsuhiko Uda

Design and development of the Flibe blanket for helical-type fusion reactor FFHR

Blanket design is in progress in helical-type compact reactor FFHR-2. A localized blanket concept is proposed by selecting molten-salt Flibe as a self-cooling tritium breeder from the main reason of safety: low tritium solubility, low reactivity with air and water, low pressure operation, and low MHD resistance which is compatible with the high magnetic field design in force-free helical reactor (FFHR). Numerical results are presented on nuclear analyses using the MCNP-4B code, on thermal and stress analyses using the ABAQUS code, and heat exchange efficiency from Flibe to He. R&D programs on Flibe engineering are also in progress in material dipping-tests and in construction of molten salt loop. Preliminary results in these experiments are also presented.

Design studies on nuclear properties on the Flibe blanket for helical-type fusion reactor FFHR

The Force-Free Helical Reactor, FFHR, is a demo-relevant heliotron-type D-T fusion reactor. The blanket design for FFHR is improved in nuclear properties by using a one-dimensional neutron transport calculation. Nuclear properties, including tritium breeding ratio (TBR), nuclear heating and induced radioactivity, are evaluated. From the viewpoints of TBR and nuclear heating, the breeding zone is divided into three layers. The first layer consists of a 100% Flibe layer for cooling the first wall and efficient transfer of thermal energy. The second layer is filled up with Be pebbles in order to increase the TBR and the interactive surface area for reducing the amount of corrosive TF (tritiated fluorine) molecules. The third layer is a 100% Flibe layer. In the improved blanket, the local TBR is 1.2 and the energy deposited in the Flibe is calculated as 55% of the total nuclear heating. The effect of nuclear transmutation on Li, Be, F is also discussed.

Comprehensive safety analysis code system for nuclear fusion reactors I: Model and analyses of overpower events for the International Thermonuclear Experimental Reactor

A comprehensive safety analysis code system has been proposed for the quantitative investigation of the safety of nuclear fusion reactors such as the International Thermonuclear Experimental Reactor (ITER). As a first step, the plasma dynamics and the thermal characteristics of the core internal structures have been developed by a one-point model and a time-dependent one-dimensional heat transfer model, respectively. The thermal behavior of ITER during overpower events caused by thermal instability of the plasma has been analyzed. In a truly ignited operation (Q [approximately] [infinity]), the plasma reaches the beta limit in [approximately]6.5 (3.5) s after insertion of a + 10% fluctuation in fuel density, when the ITER89-L power law (the offset-linear law) is applied. The surface temperature of the divertor tiles rises to [approximately]1900[degrees]C, which may result in damage from erosion and thermal stress. On the other hand, the outboard and inboard structures maintain their integrity during overpower events if the cooling systems function normally. The code system will be integrated step by step to provide overall safety analyses for nuclear fusion reactions. 37 refs., 13 figs., 1 tab.

Study of safety concept for a helical-type fusion reactor, FFHR

Safety concepts for a force free helical reactor (FFHR), of which conceptual designs have been studied in parallel with the construction of the large helical device (LHD), are presented. The main safety features expected for the FFHR are, steady-state plasma operation, no dangerous current disruptions, and the selection of a molten-salt Flibe blanket for a tritium breeder which has low tritium inventory, self cooling effect and low chemical activity. The blanket reaches such high temperatures that the tritium permeation rate increases and this tritium must be continuously recovered. Then the first wall is expected to have a low tritium inventory. Based on the classification of the plant systems and components, it is shown that the high mobility and large radioactivity release accident accompanied with the energy release is avoidable. Fundamental safety would be secured by multiple protection systems. To prevent escalation to a severe accident caused by the fracture of any of the large radioactivity confinement components, passive and reliable active protection systems are proposed. Thus, FFHR will be designed to be as safe as possible.

Comprehensive safety analysis code system for nuclear fusion reactors II : thermal analyses during plasma disruptions for international thermonuclear experimental reactor

Thermal characteristics of a fusion reactor [International Thermonuclear Experimental Reactor (ITER) Conceptual Design Activity] during plasma disruptions have been analyzed by using a comprehensive safety analysis code for nuclear fusion reactors. The erosion depth due to disruptions for the armor of the first wall depends on the current quench time of disruptions occurring in normal operation. If it is possible to extend the time up to {approximately}50 ms, the erosion depth is considerably reduced. On the other hand, the erosion depth of the divertor is {approximately}570 {mu}m for only one disruption, which is determined only by the thermal flux during the thermal quench. This means that the divertor plate should be exchanged after about nine disruptions. Counter-measures are necessary for the divertor to relieve disruption influences. As other scenarios of disruptions, beta-limit disruptions and vertical displacement events were also investigated quantitatively. 13 refs., 5 figs.

Preliminary Study of Isotopic Methanes Analysis by Laser Raman Spectroscopy for In-Situ Measurement at Fusion Fuel Gas Processing.

Application of laser Raman spectroscopy for fusion fuel gas processing was studied by measuring isotopic methanes exchanged with hydrogen isotopes, which are considered to be a major impurities in the processing. For experimental gases, isotopically equilibrated deuterium and methane were prepared in the presence of solid catalyst. Large Raman scattering peaks of v 1, bands were observed at 2,917 cm−1 for CH4 and at 2,100-2,200 cm−1 for deuterated derivatives of methane C(H,D)4. Under a spectral resolution of 5 cm−1, the v 1 bands of CH3D and CH2D2 were observed as an overlapped peak, the relative absolute Raman intensity ratio of each isotopic methane was obtained as CH4: CH3D+CH2D2: CHD3: CD4=230: 74: 144: 100. On the other hand, the Raman intensity ratio obtained from pure deuterated standard methane was CH4: CH3D: CH2D2: CHD3: CD4=230: 53: 33: 115: 105. It was confirmed that isotopically equilibrated hydrogen isotopes and methane mixed gas would be applicable for an alternative standard gas for fusion...

Application Study of Laser Raman Spectroscopy to In Situ Gas Analysis for Fusion Fuel Processing Systems

AbstractTo study the application of laser Raman spectroscopy to analysis fusion fuel processing gas, six hydrogen isotopes were experimentally measured. Raman spectra of these mixture gases showed that the useful lines for quantitative analysis are Stokes rotations below 1000 cm−1, with representative lines for H2, HD, D2, HT, DT and T2 being 587, 443, 415, 395, 250 and 200 cm−1 respectively. The absolute Raman intensity ratio was estimated as H2:HD:D2:HT:DT:T2 = 100:58:47:46:36:41. With the laser wavelength of 488 nm, power of 700 mW and using a multiple pass system, the detection limit for H2 was 10 Pa, which was the equivalent of 100 ppm in concentration. As a remote sensing technology, the optical fiber was verified as applicable for transferring the irradiation laser beam.

Application of laser Raman spectroscopy to isotopic methanes analysis in fusion fuel gas processing systems

This paper reports that to study application o laser Raman spectroscopy for fusion fuel gas analysis by an in situ method, methane (CH{sub 4}) and tritium (T{sub 2}) mixed gases were measured. In the mixed gases, hydrogen isotope exchange reactions were induced by beta decay, and various isotopic hydrogens and methanes were produced. Spectral peaks of {nu}{sub 1} and {nu}{sub 3} bands were detected individually for CH{sub 4} and four tritiated methanes. The {nu}{sub 1} bands between 1700-1900 cm{sup {minus}1} were selected as suitable ones for quantitative analysis. After mixing T{sub 2} and CH{sub 4} gases, while large amounts of tritiated methanes were produced as time lapsed, the equilibrium state was not reached by the time 1000 h had passed. It was presumed that the isotope exchange reactions were very slow compared to mixed gases of just hydrogen isotopes.