Toshio Nakagiri

Clarification of the Mechanism of Sulfur Trioxide Electrolysis : Evaluation of SO3 and O Atom Adsorbed on Pt Surface

We developed a hybrid thermo-chemical process, which included a SO3 electrolysisprocess utilizing the heat supplied by a fast breeder reactor (FBR), as a new hydrogen production process. To clarify the mechanism of SO3 electrolysis, we evaluated the electronic states of SO3 and O atom adsorbed on the Pt (111) surface using first-principles calculations with a slab model. Moreover, we evaluated the chemical bonding states of SO3 and adsorbed O using molecular orbital calculation on the basis of the calculations using a slab model. We found that there were two stable adsorbed SO3 configurations on the Pt surface. From the molecular orbital calculation, it was found that the S-O bond became weak by SO3 absorption, and it was conjectured that SO3 dissociation proceededthrough the intermediate state of adsorbed SO2 and adsorbed O on the Pt surface. Moreover, we derived the O coverage considering the adsorbed SO2 and evaluated the influence of SO3 adsorption energy on the O coverage.

Transmission imaging of sodium in the vacuum ultra-violet spectral range: new application for an intense VUV source

Metallic sodium (Na) was proposed as a transparent material in the vacuum ultra-violet (VUV) spectral range in 1930s and in 1960s. However no clear transmission has ever been demonstrated. In this paper we describe firstly the direct measurement of actual transmittance of a sodium samples in a spectral range longer than 115 nm which corresponds to the shortest transmission wavelength of magnesium fluoride (MgF2) windows, resulting in several tens of % transmittance of a 3 mm-thick solid sodium sample including MgF2 windows at the wavelength of ~120 nm. We also find very weak temperature dependency of the transmittance up to 150 degrees centigrade where the solid sample is melted at 97 degrees. The measured transmittance pushes us to make a simple imaging experiment illuminated by the VUV light through a 2-mm thick sodium sample, resulting in obtaining a clear image composed of 100 μm diameter tungsten mesh recorded on a two dimensional Charge Coupled Device detector. The result also opens a way to construct an optical imaging device for objects inside or through a solid or a liquid sodium medium. According to the present experiment, we can make a continuous real time transmission imaging for a liquid sodium sample if we use proper optical setup including an intense continuous VUV source or high repetition rated intense coherent source for holographic data acquisition. Such an experiment opens up a way to perform transmission imaging through or inside a sodium medium for characterization of hydrodynamic and material properties.

Demonstration of partially transparent thick metallic sodium in the vacuum ultraviolet spectral range

We describe the direct measurement of actual transmittance of sodium samples with thickness of a 2 mm and 3 mm in a spectral range >115 nm, resulting in >50% transmittance of 3 mm thick solid and liquid sodium samples including transmission of a pair of the windows at the wavelength of 120 nm, giving an extinction coefficient of ~10(-6) to ~10(-7) which represents the sodium with a few cm thickness to be partially transparent for this wavelength. To confirm the measurement, we perform simple imaging experiments by the ultra-violet light passing through a 8 mm-thick sodium sample to illuminate a mesh as an object, resulting in obtaining a clear image.

Hydrogen flux through the heat transfer tube wall in the steam generator of Monju

In fast breeder reactors (FBRs), hydrogen, one of the major impurities in sodium coolant, is used for water leak detection and tritium control in the interest of operating nuclear plant safety. It is essential to evaluate the hydrogen flux into the sodium coolant through the heat transfer tubes in a steam generator to understand the hydrogen behavior in an FBR plant. This study shows the time and temperature dependence of hydrogen flux using data obtained in the power rising test of the prototype FBR, Monju, and using the analysis code that can simulate the hydrogen distribution in an FBR plant. The hydrogen flux evaluated by the code gradually decreased with operating time, following the parabolic oxidation law and the Arrhenius relation over a wide range of steam temperatures. The results agreed with the hydrogen fluxes of other FBR plants evaluated in the past. It was also found that the hydrogen flux was mainly controlled by permeation through the heat transfer tubes, rather than the corrosion at the water side of the heat transfer tubes.

Evaluation of Hydrogen Transport Behavior in the Power Rising Test of Japanese Prototype Fast Breeder Reactor Monju

Tritium is essential for the evaluation of the exposed dose in the maintenance and repair work in fast breeder reactor (FBR) plants because it transfers more widely than in light water reactor (LWR) plants mainly due to the material difference of the fuel cladding and the coolant.The tritium transport and trap analysis code, TTT, has been developed by Japan Atomic Energy Agency (JAEA) to estimate tritium and hydrogen behavior in FBR plants. The TTT code was created by Iizawa et al. based on the tritium and hydrogen transport model devised by Kumar. It has been improved by data from the experimental FBR Joyo and the prototype FBR Monju. In the TTT code, it is important to deepen the understanding of hydrogen behavior which affects much for tritium behavior with the mechanisms, such as isotope exchange and coprecipitation between tritium and hydrogen.In this study, the temperature and time dependence of the hydrogen flux from the steam generator heat transfer tube of Monju in the power rising test performed in 1995 were evaluated using the TTT code. The hydrogen flux was calculated so as to simultaneously fit the measured hydrogen concentration in the primary and secondary coolant and cover gas. The flux which was attributed to the steam oxidation on the water side of the heat transfer tube in the steam generator was found to fluctuate between about 0.1 and 3.1×10−11 g H/cm2/s for the steam generator outlet temperature range from 200 to 480 °C during the reactor operation. The flux appeared to follow the Arrhenius relationship, and it almost agreed with the flux obtained in other plants in the temperature range from 330 to 380 °C. The hydrogen flux in the evaporator decreased gradually with the time of elapse to 30–40 days obeying the parabolic law, and it remained almost constant after the duration. The tendency agreed with the previous results in the 50MW steam generator test facility, which is the large scale sodium facility constructed to perform research and development for Monju.Copyright

Equilibrium Partition Coefficients of Cesium and Iodine Between Sodium Pool and the Inert Cover Gas

Equilibrium partition coefficients were experimentally measured for volatile fission products of cesium and iodine between liquid sodium pool and the inert cover gas. In the experiments, the “transpiration method” was utilized in which the saturation vapor of sodium with cesium and iodine vapor in an isothermal evaporation pot was transported by inert carrier gas and trapped by filters outside the pot. The objectives of the experiments are to: a) Obtain the equilibrium partition coefficients of cesium and iodine at high temperature between 600 and 850 deg-C, and b) Study the dependence of the partition coefficients upon the concentration in the sodium pool. From the results of previous work and this study, the following empirical equations between the partition coefficients of cesium and iodine and the sodium pool temperature could be obtained: log Kd(Cs) = 2173/T − 1.0487 (from 450 to 850 deg-C)log Kd(I) = −215/T − 0.271 (from 450 to 850 deg-C) These equations are consistent with Castleman’s theoretical equations. The partition coefficients of cesium measured at five different points of mole concentration in the pool were almost consistent with the theoretical values and decreased with the increase in the concentration. On the other hand, the measured partition coefficients of iodine increased with the increase in the concentration in the pool and this tendency was incompatible with the theoretical consideration. The reason of this discrepancy might be attributed to the formation of Na2 I2 in the cover gas.© 2010 ASME

Development of the Thermochemical and Electrolytic Hybrid Hydrogen Production Process for Sodium Cooled FBR

The thermochemical and electrolytic hybrid hydrogen production process has been developed by Japan Nuclear Cycle Development Institute (JNC). The process is based on sulfuric acid (H2SO4 synthesis and decomposition process developed earlier (Westinghouse process) and sulfur trioxide (SO3) decomposition process is facilitated by electrolysis with ionic oxygen conductive solid electrolyte at 500°C-550°C.