Ken Ichi Tanaka

In situ observation of nucleation and subsequent growth of clusters in silane radio frequency discharges

Growth processes of clusters in low-pressure and low-power silane radio frequency discharges are studied by using the newly developed double-pulse-discharge method which realizes in situ measurement of their size and density in a size range of 0.5–4 nm. The clusters begin to be composed of two size groups at about 10 ms after the discharge initiation: clusters in the small size group have an almost constant average size of about 0.5 nm through the discharge period, while those in the large one grow at about 4 nm/s in a monodisperse way. Time evolution of the measured average sizes and densities in the groups is transformed into that of size distributions assuming that the density of SinHx clusters for the small group decreases exponentially with the increase in the number of Si atoms, n, of them, and the size distribution for the large group is the lognormal one. The results show that a critical cluster size for nucleation is SinHx (n∼4).

Adsorption Characteristics of Water Vapor on Gamma-Lithium, Aluminate

Lithium aluminate (LiAl02) is one of the probable candidates for tritium breeding material because of its potential to give a fair tritium breeding ratio, stability at high temperature and stability in atmosphere containing water vapor. Clarification of the adsorption performances of water on LiAl02 is important for optimization of the way to recover bred tritium from LiAl02 and for estimation of the tritium inventory in the breeding blanket and for quantification of the hydrogen isotope exchange reaction. The amount of water captured on LiAl02 was studied in the temperature range of 373~1,100K using the breakthrough curve method, and adsorption isobar and isotherm of water on LiAl02 were proposed based on the data obtained. The water capture phenomena of LiAl02 was attributed to the dissociative chemisorption, and the apparent activation energy was determined to be 32.2 kJ/mol.K. The tritium inventory by sorption for LiAl02 was compared with that for Li20.

Study on a Method to Recover Tritium from Blanket Sweep Gas

The tritium bred in a deuterium-tritium fusion reactor is to be extracted from the tritium breeding blanket by sweep gas. To be used as fuel for the reactor, the tritium must be recovered in a form that is easy to transfer to the main fuel cycle. The feasibility of a cryosorption method that uses a porous adsorbent, such as molecular sieves or activated carbon, at liquid nitrogen temperature (77.4 K) is discussed. 19 refs., 6 figs., 4 tabs.

Isotope Effect in Cryosorption of Tritium to Molecular Sieves and Activated Carbon at 77 K

The tritium bred in a deuterium-tritium fusion reactor is removed from its blanket by using helium sweep gas mixed with some amount of hydrogen to promote the release rate. From the viewpoint of uptake capacity at the partial pressure of tritium and ease of tritium transfer to the main fuel cycle, a cryosorption bed, which uses molecular sieves or activated carbon at the liquid nitrogen temperature, is attractive for recovery of bred tritium in the blanket sweep gas. The cryosorption bed is also applicable as a transfer pump of tritium in the fuel-handling process. Tritium cryosorbedfrom a certain subunit of the fuel-handling system is transferred to other subunits by an increase in temperature and the operation of valves. It is necessary to know the adsorption isotherm and the mass transfer coefficient of each hydrogen isotope for estimation of breakthrough performances of tritium in a cryosorption bed because the mixture of tritium with other hydrogen isotopes must be treated. It is observed that the isotope effects in adsorption capacity and surface diffusivity have a close connection with the quantum effect that is represented by the reduced molecular weight. The correlative equation between Langmuir constants in the adsorption isotherm with reduced molecular weight of hydrogen isotopes is proposed. The correlative equation between surface diffusivity and reduced molecular weight is also presented.

Recovery of tritium by cryogenic molecular sieve bed in breeding blanket interface condition

Experiments were performed to obtain detailed adsorption and desorption characteristics of tritium (HT) by Cryogenic Molecular Sieve Bed (CMSB) in liquid nitrogen temperature under the simulated Breeding Blanket Interface (BBI) condition. Computer simulation analyses gave the values of separation factor and mass transfer coefficient of HT in H{sub 2}, which are very important basic parameters for the optimum design of CMSB process in BBI.

Recovery of Hydrogen Isotopes and Impurity Mixture by Cryogenic Molecular Sieve Bed for GDC Gas Cleanup

Experimental results showed that Q2 gas was adsorbed effectively by CMSB on an early stage of breakthrough even though CH4 exists in the inlet gas. Particularly, in the case of Q2 with low concentration of CH4, the break through curve of Q2 showed almost the same curve as in the case of pure Q 2 adsorption. However, CH 4 gas spilled over adsorbed Q 2 in the course of CH 4 break-through. This means that the CMSB will eventually lose the ability to adsorb Q 2 in the final stage of adsorption. The critical time when the CMSB loses the adsorption ability depends on the inlet CH 4 concentration. Analysis of the results showed that the adsorption of Q 2 and CH 4 mixture can be roughly described by assuming the multi-component adsorption equations for Q 2 and CH 4 using Langmuirs equations. It was certified that the analysis model described and predicted the experimental observations very well.

Adsorption Isotherm and Separation Factor for Multicomponent Hydrogen Isotopes in Cryosorption Method for Recovery of Tritium from Blanket Sweep Gas

The effective tritium recovery system should be designed to recover tritium from DT reactor blanket sweep gas in a form easy to transfer to the main fuel cycle. The cryosorption method using a porous adsorbent at the temperature of liquid nitrogen is one of the candidate processes for extracting tritium from hydrogen-swamped helium sweep gas because it has advantages of a large recovery capacity of gaseous tritium and good releasability of recovered tritium to the next process. In order to quantify the performance of the cryosorption method in recovering hydrogen isotopes from hydrogen-swamped helium sweep gas flow, the adsorption capacity and separation factor for multicomponent hydrogen isotope mixtures in helium on molecular sieve 4A (MS4A), molecular sieve 5A (MS5A) and activated carbon at 77.4 K were measured. 8 refs., 3 figs., 2 tabs.