Effects of Partition Wall within Packings on Separative Performances of Water Distillation for H2O-HTO Isotope Separation

For the performance assessment of H₂O-HTO isotope separation by distillation, three-dimensional internal vapor flow and concentration profiles were obtained numerically for two types of packing of 6 mm of inner diameter and 6 mm of height: One is a simple cylindrical tube (packing I) and the other diametrically partitioned with an internal wall (packing II). The results of the concentration profiles were used to estimate separative performances of the packings. The total mass transfer rate of HTO from vapor to liquid per unit area of vapor-liquid interface per unit vapor flow rate decreased with an increase in the vapor flow rate, and the value for the packing II is smaller than that for the packing I in the range of relatively small vapor flow rate. Each separative power for the packing I and II has a maximum value of 1.4×10^–7 g/s at the Reynolds number of the vapor Re_v of 54 and 3.7×10^–7 g/s at Re_v =160, respectively.     

Transient response simulation of gas separation membrane module for an atmosphere detritiation system

Transient response of a gas separation membrane module for the atmosphere detritiation system was numerically simulated with a mass transfer model. The module contains thousands of hollow fiber type polyimide membranes. The simulation model took into account permeation of water vapor through the dense layer of the membrane, diffusive transfer through the porous support layer and adsorption/desorption of water vapor into the matrix of the porous layer. The slow responses of the water vapor concentration in the retentate and the permeation rate were well reproduced by the present simulation, and transient changes in a follow fiber membrane were investigated in detail. The inventory and the mean residence time of water vapor at 303 K were estimated for the commercial membrane module (UMS-B2, Ube industries, Ltd.) as 5.7 × 10^?3 mol and 380 s, respectively.     

R134a卧式螺旋管内沸腾两相流型与传热特性实验研究

在蒸发温度为5～15 ℃、热流密度范围为5～20 kW·m^-2、工质质量流速变化范围为50～500 kg·m^-2·s^-1和干度范围为0.01～0.9的条件下,对R134a在卧式螺旋管内的沸腾两相流型及传热特性进行了实验研究。利用可视化技术对流型进行了观察分析,发现在相同工况条件下,卧式螺旋管上升段和下降段的流型有所不同,特别是形成环状流之前存在明显不同的过渡流型,分别为波环状流型和超大气弹流型,因此,对上升段和下降段分别建立了流型图。获得了传热系数随工质的干度、质量流速和热流密度等参数的变化关系,发展了R134a在卧式螺旋管内流动沸腾传热系数的计算关联式。     

Steady-State Freezing of Liquids in Laminar Flow between Two Parallel Plates

An experimental study has been conducted to investigate the effect of freezing of liquid on the heat transfer characteristics for laminar flow between two cooled parallel plates of 20 mm in distance. Both plates were maintained at the same uniform temperature which was lower than the freezing temperature of the working fluid, water. The plate wall temperature ranged -2–--7°C and the inlet water temperature was varied from 1 to 8°C. The corresponding dimensionless wall temperature θ_w, ranged 0.2–4.5. The Reynolds number was varied from 700 to 2,300. The frozen layer was smooth and had a monotonously increasing thickness as water flowed downstream. In thin layer (θ_w,≦1.1), the experimental results agreed well with the analytical calculations. In thick layer (θ_w,>1.1), however, the measured layers were thinner than the calculated values since the fluid acceleration due to flow area reduction might produce an enhancement in heat transfer, which was neglected in the theory.     

Condensing Heat Transfer in Steam-Water Condensing-injector

An experiment on the direct heat transfer process between supersonic steam and subcooled water jet was performed, using a steam-water condensing-injector. Photographic observation provided information on the state of flow, and establishment of a critical separate steam-water flow was confirmed. The temperature and pressure distributions along the flow were measured and the effective coefficients of condensing heat transfer were evaluated from the observed data, based on a model embodying an idealized interface between vapor and liquid. In the vicinity of the water nozzle exit, where the vapor-liquid interface was distinct, the heat transfer coefficients obtained were 14–28 (cal/°C.cm².sec), and some correlation was observed among Nusselt, Reynolds and Jakob numbers, upon adopting the velocity and the physical properties of the steam phase. The relations Nu=6.0.Re ^0.9(Pr=1.04–1.10), and Re=1.8×10⁸.Ja ^3.0, i.e., Nu=1.6×10⁸.Ja ^2.7 were derived as a rough estimation. No clear correlation could be discerned in the corresponding data obtained from observation points further downstream, where a distinct steam-water interface no longer existed. In conclusion, it is proposed that, in deriving the correlations between Nu and Re or Ja, the physical properties of the vapor and the vapor-liquid relative velocity should be adopted, on account of the strong dependence of condensing heat transfer on steam velocity and water subcooling.     

The Hydrothermal System Beneath Owakudani on Hakone Volcano,Japan; Traced by Stable Isotopic Ratios of H2O

In this study, we sampled natural fumarolic gases, the gas from a steam well drilled to 800 m depth and natural hot spring waters from the Owakudani geothermal area, Hakone Volcano, Japan. We then measured the chemical composition and the D/H and ¹⁸O/¹⁶O ratios of H₂O within the samples. On the basis of the analytical results, we investigated the differentiation processes of the magmatic fluid during ascent to the surface. Volcanic gas discharged from the No. 52 steam well has a CO₂/H₂O ratio that is much higher than those from fumarolic gases. The isotopic ratio of H₂O in the gas are also much higher than those in the fumarolic gases, and the gas also contains high concentrations of SO₂ and HCl. The above observations indicate a magmatic origin for the gas from the No. 52 steam well. The hydrothermal system is principally explained by the mixing of a magmatic vapor, represented by the gas from the No. 52 steam well, and cold local meteoric water. Following mixing of the fluids, a separation of primary vapor and liquid occurs. The primary liquid is discharged as a component of hot spring water, and has high isotopic ratios. The primary vapor is mixed with vapor derived from the boiling of local meteoric water. The mixed vapor is then discharged to the surface, interacting with shallow meteoric water and undergoing partial condensation of H2O vapor. Hot spring water with isotopic ratios lower than those of the primary liquid is derived from the boiling of local meteoric water.     

Radiolytic hydrogen evolution in a closed vessel

Radiolytic hydrogen gas evolution under the liquid-gas two-phase condition has been studied using a closed vessel and γ -rays from a Co-60 source to develop an evaluation method for the H₂ evolution amount during transfer and storage of radioactive materials. An experiment was conducted using a closed vessel in which air and aerated pure water were present at room temperature. Several vessels were irradiated once with ?-rays at 5.2 × 10³ Gyh^–1. It was found that apparent G-values of H₂ production, calculated with a pressure increase of the closed vessel, became smaller for the cases of higher ratio of gas phase volume to liquid phase volume due to the recombination reaction of radiolytic H₂ with O₂ and H₂O₂. Also, equilibrium H₂ partial pressure became 10 times higher than the expected value using Henry’s law. These behaviours were explained by the developed model, which includes the liquid-gas distribution ratio of radiolytic H₂, the equation of state for H₂ in the gas phase, and the effective volume of liquid phase relevant to the liquid-gas distribution under the irradiation conditions. The effective volume of liquid phase was determined by considering the extent of the recombination reaction of radiolytic H₂ during mass transfer from the liquid phase to the gas phase.     

Combined Forced and Free Convective Heat Transfer Characteristics in a Narrow Vertical Rectangular Channel with 2.5 mm in Gap Heated from Both Sides

Heat transfer characteristics of mainly combined forced and free convective flow in a vertical rectangular flow channel with a gap of 2 5 mm, which was quite narrow compared with those investigated in previous experiments, were studied experimentally for water. As a result, the following heat transfer characteristics were made clear, using a non-dimensional parameter Gr _x /Re ²¹ _x /⁸ Pr ^1/2 similarly to the case for the 18 mm gap which was already reported by the authors.

(1) When the Gr _x /Re ²¹ _x /⁸ Pr ^1/2 is less than 10^?4, both upward flow and downward flow show the nature of forced convective heat transfer.

(2) When the Gr _x /Re ²¹ _x /⁸ Pr ^1/2 is between 10^?4 and 10^?2, heat transfer coefficients for both upward flow and downward flow are higher than any of those predicted by the previous correlations for turbulent forced convection along a flat plate and turbulent free convection along a vertical flat plate. This is, differently from the case of 18 mm gap, due to the effect of the acceleration of main flow induced by the development of the boundary layer along the channel.

(3) When the Gr _x /Re ²¹ _x /⁸ Pr ^1/2 is larger than 10^?2, the upward flow shows the nature of free convective flow even with the gap as narrow as 2.5 mm in the vertical rectangular flow channel. Heat transfer correlations which have been developed for the 18 mm gap channel, are also available for the described-above regions of 2.5 mm gap channel.     

Pressure Balanced Type Membrane Covered Polarographic Oxygen Detectors for Use in High Temperature-High Pressure Water, (II)

Performance tests of a pressure balanced type membrane covered polarographic oxygen, detector were carried out in water at 285°C (BWR operating conditions) to determine the effects of environmental factors. Dependencies of detector current on pressure and sample water flow velocity were ascertained and response time of the detector was determined. Effects of H₂ present in the water were also examined. The following conclusions were obtained:

1. The detector current increased in proportion to the 0.67th power of the flow velocity, but was independent of the pressure.

2. Response time was about 7 s.

3. Hydrogen caused a decrease in the current at cathode potentials more positive than ?0.75 V against the Ag/AgCl electrode. However, at more negative potentials, the current was independent of H₂ concentration and in proportion to O₂ concentration.

Oxygen concentrations in water containing H₂ at 285°C could be determined by the detector under the measurement conditions of constant flow velocity and cathode potentials more negative than ?0.75 V.     

Study on the Rate and the Products of the Reaction between Uranium Monocarbide and Water

With the use of a flow reactor, the products and the rate of reaction between UC powder and water were studied for the case of liquid water and water vapor under 20–100 mmHg at 80°C and other temperatures. The oxide produced in the reaction with water vapor was determined to be UO₂ by chemical analysis. The reaction rate and the gaseous products were measured by means of a gas Chromatograph.

Neither the rate nor the products showed any marked difference between water and water vapor. This indicates that the two reaction proceed by a similar mechanism. As the temperature was raised further, the evolution of H₂ C₂H₆, C₃H₈, C₃H₆, etc. increased while that of CH₄ decreased.

The rate of the evolution of gaseous products can be expressed in the form R=const. ×thetan where θ is the coverage of water on the carbide. The values of n were found to be 1.0 for CH_4t and 0.53 for H₂. Those for the C₂, C₃ and C₄ components were 1.0 for the high coverage region and less than unity for those of low coverage. This could be attributed to non-uniformity of the carbide surface.     

Condensation in the presence of noncondensable gases

An experimental investigation to examine the effects of surface orientation on the condensation of steam in the presence of noncondensable gas is reported. An air-steam mixture was directed into a rectangular flow-channel over a condensing aluminum surface that has a painted surface finish. The mixture flow was concurrent in all the tests with condensate flow. In this series of experiments, the orientation of the condensing surface was varied from 0–90° (plate surface was facing downwards at 0°), with a variable air-steam mass fraction of 0–0.87, and a mixture velocity of 1–3 m/s. The heat transfer coefficient was measured in addition to making visual observations of the condensation process. It was found that the heat transfer coefficient varied from 100 to 600 W/m² K with the mass fraction of 0.87-0.24 and the maximum heat transfer coefficient of 6200 W/m² K was measured with mass fraction of 0. By tilting the condensing surface from the horizontal to vertical position, the heat transfer coefficient decreased 15 to 25% depending on the mass fraction. With a higher vapor content the effect of the orientation was smaller. This dependence was attributed to the existence of interfacial structure (droplets and ridges) that promoted heat transfer at small inclination angles, when the angle was increased the interface became smoother and heat transfer rates decreased. Heat transfer rates were also observed to increase with flow velocity, vapor content and pressure. The results are compared with some previously published data and a proposed condensation model that showed reasonable agreement with the data trends.     

Mass transfer process of hydrogen via ceramic proton conductor membrane of electrochemical hydrogen pump

The blanket tritium recovery system using the electrochemical hydrogen pump with proton conductor membrane has been proposed. The feature of the electrochemical hydrogen pump is that the driving force of hydrogen transportation is a potential difference. Therefore, it might be effective to apply the hydrogen pump to the blanket sweep gas (the low hydrogen and water vapor pressure). Perovskite-type ceramic such as SrCe_0.95Yb_0.05O_3−α, is one of the candidate proton conductor for hydrogen pump and its ionic hydrogen transportation properties have been investigated. In this work, the basic mass transfer equation for hydrogen, in which the apparent proton conductivity is used as the over-all mass transfer coefficient, is proposed. And then, the apparent proton conductivities were estimated from experimental data using these equations, and mass transfer of hydrogen via proton conductor membrane was discussed by using the apparent conductivity.     

Significance of Covariance Matrices in Nuclear Data Evaluation

Tritium decontamination using ultra violet (UV) lamp and laser was performed. Simulated co-deposited layer on tungsten substrate was deposited by C₂H₂ or C₂D₂ glow discharge. The co-deposited layer was irradiated to UV lights from a xenon excimer lamp (172 nm) or ArF excimer laser (193 nm) and the in-situ decontamination behavior was evaluated by a mass spectrometer. After the UV irradiation, the hydrogen concentration in the co-deposited layer was evaluated by elastic recoil detection analysis (ERDA) and the depth profile was analyzed by secondary ion mass spectrometry (SIMS).

For the co-deposited layer formed by C₂D₂ glow discharge, it was found that M/e 3 (HD) gas was released mainly during the UV lamp irradiation while both M/e 3 (HD) and M/e 4 (D₂) gases were detected during the UV laser irradiation. Though the co-deposited layer was not removed by UV lamp irradiation, almost all the co-deposited layer was removed by UV laser irradiation within 1 min. The ratio of hydrogen against carbon in the co-deposited layer was estimated to be 0.53 by ERDA and the number of photon needed for removing 1 fim thick co-deposited layer was calculated to be 3.7×10¹⁸ cm^-2 for the UV laser by SIMS measurement. It is concluded that C-H (C-D) bond on the co-deposited layer were dissociated by irradiation of UV lamp while the co-deposited layer itself was removed by the UV laser irradiation.     

Numerical Analysis on Heavy Water Separation Characteristics for Pair of Bithermal Trickle-Bed Type H2/H2O-Exchange Columns

In order to study how the operating pressure and temperature have influence on the heavy water separation characteristics for a pair of bithermal trickle-bed type H₂/H₂O-exchange columns packed with the hydrophobic Pt catalyst, the authors utilized the analytical expressions derived from the differential equations expressing the material balance of the three components, hydrogen, water vapor and water in the exchange column.

The cases where the operating temperature in a hot column is 200°C, the deuterium enrichment factor is 3, the hydrogen superficial velocity is (0.2)×(Operating pressure (atm)) (Nm/s) and the column efficiency is high and low were studied. As the results, the optimum operating pressure is about 50 atm in both cold and hot column, the optimum operating temperature in a cold column is 100°C and other important parameters such as the optimum length of a cold and a hot column, the optimum hydrogen to feed water molar flow ratio and the optimum degradation ratio were also obtained.     

Transfer of tritium in concrete coated with hydrophobic paints

An experimental study on tritium (T) transfer in porous concrete for the tertiary T safety containment is performed to investigate (i) how fast HTO penetrates through concrete walls, (ii) how well concrete walls contaminated with water-soluble T are decontaminated by a solution-in-water technique, and (iii) how well hydrophobic paint coating works as a protecting film against HTO migrating through concrete walls. The experiment is comparatively carried out using disks of cement paste which W(water)/C(cement) weight ratio is 0.6:1 with or without hydrophobic paints, and mortar disks which W/C/sand ratio is 0.6:1:2 with or without the paints. The hydrophobic paints tested in the present study are an epoxy polymer resin paint and an acrylic-silicon polymer resin one. After T exposure during specified time under a constant HTO vapor pressure in an acrylic box, the amount of water-soluble HTO on/in the disks is determined using a technique of H₂O dissolution during specified time. The results obtained here are summarized as follows: (1) HTO penetration in porous concrete can be correlated in terms of the effective diffusivity. (2) Its value in porous cement without coating is 1.2 × 10⁻¹¹ m²/s at 25 °C. (3) HTO penetrates only through pores in cement, and there is no path for HTO transfer in non-porous sand. (4) Rates of sorption and dissolution of HTO in disks of cement and mortar coated with the epoxy resin paint are correlated in terms of the effective diffusivity through the paint film which value is D_T = 1.0 × 10⁻¹⁶ m²/s. The rate-determining step is diffusion through the paint. (5) The epoxy resin paint works more effectively as an anti-HTO diffusion coating. (6) Another acrylic-silicon resin paint does not work well as anti-HTO diffusion coating. This may be because the hydrophobic property of the silicon resin paint is deteriorated with elongating the contact time with H₂O vapor or liquid. (7) The HTO uptake inside the epoxy paint is greater than that of the silicon one. (8) The permeation reduction factor (PRF) of HTO for the epoxy paint at steady-state is expected large, if HTO vapor only contributes to diffusion. However, when concrete surfaces coated with the epoxy paint are under wet conditions, the PRF value becomes smaller. All those results can be used to estimate the effect of HTO soaking in concrete walls in case of accidental T release in a fusion reactor room and to decontaminate wastes of tritiated concrete.     

An experimental investigation of a passive cooling unit for nuclear plant containment

A set of condensation experiments in the presence of noncondensables (e.g. air, helium) was conducted to evaluate the heat removal capacity of a passive cooling unit in a post-accident containment. Condensation heat transfer coefficients on a vertically mounted smooth tube have been obtained for total pressure ranging from 2.48×10⁵ Pa(abs) to 4.55×10⁵ Pa(abs) and air mass fraction ranging from 0.30 to 0.65. An empirical correlation for heat transfer coefficient (h), has been developed in terms of a parameter group made up of steam mole fraction (Xs), total pressure (P_t), temperature difference between bulk gas and wall surface (dT). This correlation covers all data points within 20%. All data points are also in good agreement with the prediction of the diffusion layer model (DLM) with suction and are approximately 2.2 times the Uchida heat transfer correlation. Experiments with an axial shroud around the test tube to model the restriction on radial flow experienced within a tube bundle demonstrated a reduction of the heat transfer coefficient by a factor of about 0.6. The effect of helium (simulating hydrogen) on the heat transfer coefficient was investigated for helium mole fraction in noncondensable gases (X_He/X_nc) at 15, 30 and 60%. It was found that the condensation heat transfer coefficients are generally lower when introducing helium into noncondensable gas. The difference is within 20% of air-only cases when X_He/X_nc is less than 30% and total pressure is less than 4.55×10⁵ Pa(abs). A gas stratification phenomenon was clearly observed for helium mole fraction in excess of 60%.     

Determination of γ-spectrometric parameters for Na2CO3 and H2O in Na2CO3-water solution

The mass attenuation coefficients of Na₂CO₃ solved in water was measured for Na₂CO₃ contents up to 0.191 g of salt in cm³ of water at the energy of 0.662 MeV emitted from ¹³⁷Cs. On the basis of the mixture rule the mass attenuation coefficients were calculated for the solutions at each salt content. Comparison between the measured and calculated values revealed, in general, those experimental values of linear and mass attenuation coefficients are smaller than the calculated ones. The total atomic cross-sections and effective atomic numbers were obtained for the mass attenuation coefficients. Least square method has been applied to determine the mass attenuation coefficients, atomic cross-sections, and the effective atomic numbers of Na₂CO₃ and water, separately, in the solution and compared with the corresponding calculated values.     

Vaporization and deposition of cesium dimolybdate,Cs2Mo2O7

Vaporization and deposition of cesium dimolybdate (Cs₂Mo₂O₇) in argon were studied by thermogravimetry and transpiration methods. From Raman spectra and electron probe microanalysis of deposits and inductively coupled plasma mass spectroscopy of the aqueous trap of the exhaust, it was judged that the Cs₂Mo₂O₇ vaporizes as Cs₂Mo₂O₇ (g). The effect of water addition on Raman spectral of Cs₂Mo₂O₇ was also investigated. Comparing the high-temperature mass losses of Cs₂Mo₂O₇ by thermogravimetry with that of Cs₂MoO₄, the equilibrium vapor pressure of Cs₂Mo₂O₇ was estimated. The vapor pressure of Cs₂Mo₂O₇ (l) in its liquid state was calculated to be: log₁₀P (Cs₂Mo₂O₇)(l) = (8.95 ± 0.07) ? (1.03 ± 0.01) × 10⁴ /T (T = 1273?1573 K). The enthalpy of vaporization of Cs₂Mo₂O₇ (l) was estimated to be 197 ± 31 kJ·mol^?1.     

Heat transfer and thermal conductivity of multi-hundred watt 238PuO2 fuel spheres

The thermal conductivity of porous ²³⁸PuO₂ has been calculated from steady-state core and surface temperatures in spheres having diameters of ≈ 3 and ≈ 3.7 cm assuming linear heat transfer at the sphere surface. The spherical fuel forms had densities of 80 to 85% of T.D. for PuO₂ (T.D. = 11.41 g/cm³). Thermal conductivity in the fuel increased nearly linearly with [$\text{T}{}_{\mathrm{<mtext>avg</mtext>}}\text{(}\text{K}\text{)]}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ in the range 350–1100°C and thus was dominated by a gas phase present in the open and closed porosity of the fuel. For spheres heated in helium or vacuum, the gas phase had essentially three degrees of freedom. When the fuel was heated in argon saturated with water vapor, approximately 50 degrees of freedom were indicated and this was apparently largely due to the water vapor. A two-phase, series slab heat flow model adequately predicted the thermal conductivity of the ²³⁸PuO₂ phase as a function of temperature.     

Effects of water-to-cement ratio and temperature on diffusion of water in hardened cement pastes

Apparent diffusion coefficients (D_a) of water and activation energies (E_a) of diffusion in hardened cement pastes (HCPs) were determined as a function of water-to-cement (w/c) ratio (0.36–0.60) and temperature (293–323 K) using HTO and H₂¹⁸O as tracers. The values of D_a and E_a ranged from 1.1×10^?11 to 1.7×10^?10 m² s^?1 and from 21.5 to 31.3 kJ mol^?1, respectively. No significant difference between the D_a values of HTO and H₂¹⁸O suggests that water predominantly diffuses as H₂O molecule and dissociation of water is not significant even at high pH range in HCP. The values of E_a at low w/c ratio were higher than in bulk liquid water, suggesting a contribution of a different water regime, such as supercooled bulk water. Two simple models consisting of capillary and gel pores were considered to estimate the volume ratio of gel pores to total pores by optimizing the model to fit with the experimental data. The result suggests that HCP has a pore network mostly consisting of capillary pores with some very narrow pores plugged with hydrates, where HTO must diffuse through gel pores. This view of the HCP pore network was made available through analysis of E_a values.