Numerical Analysis of Separative Power of Isotope Centrifuges, (II)

It is found from numerical analysis that a strong influence is exerted on the separative efficiency of centrifuges by the thermal convection arising from the temperature difference prevailing between the end plates of a centrifuge drum—known as “Ekman suction”. The numerical method previously developed by Nakayama & Torii is used to compute the distributions of concentration resulting from considerations of both thermal convection and forced flow.

The effect of Ekman suction is represented by the parameter λ_E(≡(a²√E _ρpsV?T)/(16 lρDT₀)), different values of which were adopted in the calculations, as were other parameters such as λ(≡G_F/(?ηlρpD), G_F: feed rate) for the forced flow and θ representing the cut. The separative efficiency of an exemplified counter-flow type centrifuge is found to reach 58% when λ_e≒0.7, λ≒1.0 and θ≒O.3, with a product port radius r _p= 0.5.

It is also shown that the thermal convection in the Stewartson layer near the side wall of a centrifuge drum affects the separative, efficiency to relatively small but not negligible extent.     

Oxygen Potential of Cs2U4O12/Cs2U4O13 Equilibrium

A batch distillation of tritiated water (～10 nCi/cm³) has been performed in a packed column 1.6cm inner diameter x 100 cm high. Packings were Dixon rings made of SUS. Time variations of tritium activity were measured by changing vapor flow rate within the column, and then the separative performances, such as the separation factors and the separative power per unit charge, were obtained. The maximum values of the total separation factor and the separative power per unit charge were 1.45 and 2.0x10^?2, respectively. The vapor flow rate from the reboiler decreases as the batch operation proceeds, so that a simulation with a fixed stage-number, the usual case, could not sufficiently predict the experimental values. We have therefore developed a simulation procedure where the number of hypothetical stages can be changed during the batch operation in order to predict the dynamic column behavior obtained from the experiments. The simulation result with the variable stage-number agreed with the experimental one.     

Si同位素分离单机供料流量的优化

介绍了二元和多组分同位素混合物的分离功率表达式。以SiHCl3（硅氯仿）为工作气体,在分离装置上进行单机分离实验,得到了供料流量与各分离性能参数之间的关系。结果表明,当供料流量在20克每小时附近时,单机分离性能最佳。     

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.     

Measurement of Liquid Turbulent Structure in Bubbly Flow at Low Void Fraction Using Ultrasonic Doppler Method

Microscopic structure in bubbly flows has been a topic of interest in the study of fluid dynamics. In the present paper, the ultrasonic Doppler method was applied to the measurement of bubbly. The experiments were carried out for an air-water dispersed bubbly flow in a 20 mm × 100 mm vertical rectangular channel having a void fraction smaller than 3%. Two ultrasonic transducers were installed on the outer surface of the test section with a contact angle of 45^° off the vertical axis, one facing upward and the other facing downward. By applying statistical methods to the two directional velocity profiles, Reynolds stress profiles were calculated. Furthermore, to clarify the wake effect induced by the leading bubbles, the velocity profiles were divided into two types of data. The first one is for all of the liquid data and the other is the data which did not include the wake effect. For Re_m ≥1,593, it was observed that the bubbles suppressed the liquid turbulence. Furthermore, comparing with the Reynolds stress profiles in bubbly flow, it was found that Reynolds stress profiles varied with the amount of bubbles present in the flow and the effect of wake causes turbulence in the liquid.     

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.     

Additive Property of Separative Power

A separative power of a separating element, whose heads and tails separation factors are α and β is expressed by φ _b (α, β)= [α(β-1)1n α-(alpha;-1) in β]/(α β-1) for the unit flow of the desired material and φ _a (α, β) (≡ φ _b (β, α) for that of undesired material. The additive properties of the functions φ _b and (φ _a were demonstrated by calculations of various types of ideal cascades, but the origin of the property is not obvious. The present study has furnished the mathematical basis of the additivity based on the special functional equation. First, for symmetric processes (α, β), the functional equation which describes the function representing the quality of separation f(α, α) concerning the desired material was obtained and solved to give the functional form of f(α, α,). The result was extented to the function f(α, β) representing the quality of asymmetric separation (α, ≠ β). The derived function f(α, β) was demonstrated to be equal to φb(α, β)and it was verified that functions φb(α, β) and φ _a (α, β) have the additive property in themselves.     

1993 National Symposium on Atomic Energy,Tokyo, Japan

A steady-state simulation model of the gas separation system using a hollow-filament type membrane has been proposed. The mass transfer coefficients in the non-porous thin layer, in the porous support layer of the membrane and in the boundary layer of the membrane surface are estimated in the model. The four types of flow patterns: cross flow, mixing flow, concurrent flow and counter current flow, are also considered in the model. The mass transfer through the non-porous thin layer of the membrane controls the overall mass transfer by ~99%. The experimental observations of TPL (Tritium Process Laboratory in JAERI) for N₂–H₂ and Air—H₂ systems agreed with the calculated results of the cross flow under a set of typical conditions (disposal volume of 2.78×10^?3 Nm³/s, feed-side pressure of 3.44×10⁵Pa, and permeated-side pressure of 1.07×10⁴ Pa). The validity of the simulation method was thus proved. For Air-H₂-H₂O system also, the recovery ratios calculated for H₂ are in good agreement with the experimental observations. However, the calculated recovery ratios of water vapor were slightly smaller than the experimental observations. This discrepancy may result from the difference in separation mechanism between H₂ and water vapor, or the construction change of membrane caused by the existence of water vapor.     

The Effect of Vibration on Critical Heat Flux in a Vertical Round Tube

This paper deals with the results of experimental investigations on the effects of tube vibration on critical heat flux (CHF) in order to gain an understanding of the relationship between CHF and flow-induced vibration (FIV). The experiment was carried out in the following range of parameters: diameter (D)=0.008 m; heated length (L)=0.2, 0.4 m; pressure (P)=101 kPa; mass flux (G)=403–2,551 kg/m².s; quality (x)=-0.045–0.289; amplitude (a)=0.0001–0.001 m; frequency (f)=0–70Hz. The CHF generally increases with vibration intensity, which is represented by vibrational Reynolds number (Re _v ); the CHF enhancement is more dependent on amplitude than on frequency. CHF enhancement seems to come from the reinforced flow turbulent mixing effect by vibration in the vicinity of heat transfer surface. Based on the experimental results, an empirical correlation is proposed for the prediction of CHF enhancement by tube vibration. The correlation predicts the CHF enhancement ratio (En) with reasonable accuracy, with an average error rate of -2.18% and 27.75% for RMS.     

Numerical Calculation of H2-HT Separative Performances up to −0.3 MPa of Thermal Diffusion Column with Fairly Higher Hot-Wire Temperature

By using the two-dimensional rigorous numerical solution of flow and convection-diffusion equations, the H₂-HT separative performances of thermal diffusion column with 15 mm-radius and 288.15K cold-wall was analyzed up to ?0.3 MPa for higher hot-wire temperature (up to ?1,700K). Flow analysis has revealed: (1) The magnitude of the free convection is almost proportional to the pressure, and laminar solution of free convection could not be obtained at the pressure more than ?0.32 MPa. (2) The magnitude of the free convection increases gradually with ΔT (the temperature difference between hot and cold surfaces), when ΔT<–800 K. In the range of larger ΔT, the magnitude is almost constant or rather decreases gradually with ΔT. As a result, the laminar solution could always be obtained at the pressure less than ?0.32 MPa, no matter how large ΔT may be. Separative analysis for H₂-HT isotope separation has made clear that the thermal diffusion column with 288.15 K cold-wall should be operated at (1) 0.15–0.2 MPa, (2) ΔT that is as large as technically possible, and (3) the feed rate F of 50–100 cm³ (288.15 K, 0.1 MPa)/min.     

Development of 160 m3/min Large Capacity Sodium-Immersed Self-Cooled Electromagnetic Pump

A large capacity sodium-immersed self-cooled electromagnetic pump (LEMP) was developed for application to the main circulation pumps of FBR. This advanced LEMP is a submergible annular linear induction pump designed to be self-cooled by immersing into sodium and applying high temperature electrical insulation. Almost all the internal electrical losses were transferred to the surrounding sodium, which can be recovered as electricity by turbine generators. The LEMP having specifications of 160m³/min flow rate, 0.28 MPa head and more than 40% efficiency at the rating was designed, fabricated and tested in the sodium pump test facility. The test involves magnetic field measurement in the air and a variety of sodium tests during 2,550 h, which demonstrated good pump performance and flow controllability, and satisfied the design target. The boundary between flow stability and instability of the LEMP operation could be defined by peak position of the Q-H curve, which was specified by Re_m×S (magnetic Reynolds' number times slip) of 1.4 to 1.5 at 335°C. Based on the test results, the applicability of the LEMP for the FBR was confirmed.     

Effect of Changes in Feed Rate and Cut on Circulating Flow within Thermal Diffusion Column for Isotope Separation

A two-dimensional axisymmetric convectional flow field of an isotope separating thermal diffusion column with continuous feed and draw-offs is analyzed through the Newton iterative numerical solution of the equations of change without the Boussinesq approximation. Computations are performed for Ar gas within an inner hot radius of 0.2 mm and an outer cold radius of 5 mm, between which the temperature differs by 300 K. The rate of feed F, supplied into the middle point of the column, is varied from 1 to 5 cm³/s, while the cut θ, or the ratio of the upper drawing-off to feeding rates, from 0.1 to 0.9. Comparison of flow vectors, temperature and density profiles among various sets of (F, θ) makes it clear that the flow fields agree with one another for the same value of the total transport; that is, θF_pc (pc: feed gas density) in the upper section and -(1-θ)pc in the lower section of the column. Observations on the mass flow vectors near the feed slit lead to the finding that the multiplicative effect of separation cannot be expected in the column with the inner radius r_c of 5 mm at the feed rate F exceeding 2 cm³/s(i.e F/ΔTr_c ⁴ )>0.1 [1/(s·K·cm)]), because the feed flow interrupts the whole-length circulation of the natural convection.     

Separative Power of 2-Up 1-Down Ideal Cascades

Interstage flows are analyzed for ideal cascades composed of asymmetric separation elements. It is shown that, in such a cascade, the separative power is additive, that is, the summation of the separative powers of all stages equals the total separative power of the ideal cascade composed of asymmetric separators. This is proved by calculation establishing that the total sum of interstage flows is equal to that obtained by dividing the total separative power of the cascade by the separative power per unit flow of the elements. A similar additive property is also evidenced for separative powers relevant to the desired and undesired materials. As a concrete example, a 2-up 1-down cascade is discussed.     

Vold Fraction Correlation for Boiling and Non-Boiling Vertical Two-Phase Flows in Tube

Abstract

Applicability of previously proposed Vold fraction correlation was studied on the boiling steam-water flows in tube. The correlation was found to be applicable to the data of Sekoguchi (d=13.55 mm) and Bartolomei (d=25mm), i.e. the value of parameter K in the correlation equals to unity. The average value of K for pipes of smaller diameter (d= 6.1, 7.7 mm) was 0.57 for both adiabatic and diabatic steam-water flows. These values of k are not dependent on flow regime, heat flux and superficial water velocity within the investigated ranges. A criterion was established with a dimensionless group Eoλ which determines the K-value as: K=1.0 for Eoλ≧2×10⁶ and K=0.57 for Eoλ<2×10⁶.

A comparison between the predicted values by this method and experimental values at pressures from atmospheric to 80 kg/cm² abs., heat fluxes 0–1.5×10⁶ kcal/m²-hr, pipe diameters 5–76.2mm and gas-water volumetric flow ratios 0.06–10⁴, showed that the present correlation is adequate within ±15% of deviation.     

Combinated Flow Pattern Map for Cocurrent and Countercurrent Air-Water Flows in Vertical Tube

Flow patterns for cocurrent and countercurrent air-water flows in vertical tubes (40 and 80mm I.D.) at volumetric flux densities of air and water in the ranges ?115–158 and ?100–102 cm/s were observed. A flow pattern map presenting the entire data of the observed flow patterns, i.e. bubbly, slug and annular flow for each mode of flow operation (upflow, countercurrent flow and downflow) were presented on the j_l vs. j_g plane. The flow pattern maps showed significant difference of flow pattern transition boundaries with upflow, countercurrent flow and downflow. Flow pattern transition curves were smoothly continuous with the change of the direction of water flow, on the other hand the change of flow direction of air showed complicated effect on flow pattern transition near zero j_g . Comparison of the present flow pattern data with the reported general flow pattern maps for upflow showed that the correlation of Taitel et al. for bubble-slug flow transition is applicable to both cocurrent and countercurrent air-water flows.     

Optimum Cut of Separating Element as Function of Total Separation Factor and Mole Fraction of Component to be Separated

For a simplified model of separating elements where a total separation factor αβ is independent of values of cut ? (0≤?≤1), an optimum cut ?_opt in the sense that the cut makes a separative power δU maximum, was derived in terms of αβ, and a mole fraction x_F (0≤x _F≤1) of the component to be separated. When values of x^F is nearly equal to zero, the optimum cut ?^xF _opt?0 decreases and approaches to near 0, as the total separation factor becomes larger. On the contrary, when x_F is nearly equal to 1, the optimum cut ?^xF _opt?1 was found from calculation to be 1-?^xF _opt?0, and increases and approaches to near 1, as the total separation factor becomes larger. Moreover, in the case of x_F =0.5, the optimum cut is 0.5 regardless of αβ. Generally, the optimum cut ?_opt(x_F ) was solved to be in the form of a linear interpolation of the boundary values, ?x^F _opt?0 and ?x^F _opt?1.     

Detritiation of Glovebox Atmosphere by Using Compact Tritium Removal Equipment

A compact tritium removal equipment (TRE), assembled in a console with casters, has been developed for detritiation of air in a glovebox used for handling of several curies of tritium. The TRE was designed to remove gaseous tritium in the form of T₂, HT and CH₃T through oxidation with precious metal/alumina catalysts followed by adsorption on zeolite pellets.

From the detritiation experiments with hydrogen tritide (HT, 2–20 mCi), the TRE was confirmed to have sufficient performance for the practical use. The tritium concentration in the test gas (total volume –32l; 1%H₂, 5%O₂, 94%N₂) decreased from 0.64 to 6.4 ×10-⁷ Ci.m³ within 155 min when the TRE was operated under the recirculation mode with the flow rate of 200 l-h¹ at the catalyst temperature of 200°C. In addition, the HT-to-HTO fractional conversion was determined at various catalyst temperatures (25–200°C) and flow rates (100–360 lh-¹).     

Room-Temperature Reactor Packed with Hydrophobic Catalysts for the Oxidation of Hydrogen Isotopes Released in a Nuclear Facility

A room-temperature reactor packed with hydrophobic catalysts for the oxidation of hydrogen isotopes released in a nuclear facility will contribute to nuclear safety. The inorganic-based hydrophobic Pt catalyst named H1P has been developed especially for efficient oxidation over a wide concentration range of hydrogen isotopes at room temperature, even in the presence of saturated water vapor. The overall reaction rate constant for hydrogen oxidation with the H1P catalyst in a flow-through system using a tritium tracer was determined as a function of space velocity, hydrogen concentration in carriers, temperature of the catalyst, and water vapor concentration in carriers. The overall reaction rate constant for the H1P catalyst in the range near room temperature was considerably larger than that for the traditionally applied Pt/Al₂O₃ catalyst. Moreover, the decrease in reaction rate for H1P in the presence of saturated water vapor was slight compared with the reaction rate in the absence of water vapor due to the excellent hydrophobic performance of H1P. Oxidation reaction on the catalyst surface is the rate-controlling step in the range near room temperature and the rate-controlling step is shifted to diffusion in a catalyst substratum above 313K due to its fine porosity. The overall reaction rate constant in the range near room temperature was dependent on the space velocity and hydrogen concentration in carriers. The overall reaction rate constants in the range of 1;000=T greater than 3.2 correlated to k _overall[s^?1] = 5.59 × 10⁷ × SV[h^?1] × exp (?67.7 [kJ/mol]/R_gT), where the space velocity range was from 600 to 7,200 h^?1.