Numerical Analysis of Pressure Effects on Heavy Water Separation Characteristics for a Pair of Dual Temperature Multistage-Type H2/H2O-Exchange Columns

In order to study how the operating pressure has influence on the heavy water separation characteristics for a pair of dual temperature multistage-type H₂/H₂O-exchange columns, the authors utilized the analytical expressions derived from the finite difference equation describing the material balance in the exchange column. The separation characteristics of the system were studied theoretically under the conditions where the temperature in a hot column t_h=200°C, the pressure in a hot column π≦50atm and the pressure in a cold column π = 5–50atm.

As the results, the optimum modified specific column volume v^*_opt decreases with the increase of π and then keeps the nearly constant value, and is smaller at ≦=50atm than at ≦=30atm in the case where the temperature in a cold column t_c is constant. Other important parameters such as the optimum operating temperature in a cold column t_copt the optimum numbers of stages in a hot column M_opt and in a cold column t_opt, the optimum hydrogen to feed water molar flow ratio γ _opt and the optimum degradation ratio δ_opt were also calculated.     

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.     

Digital Void Velocimeter

The paper describes the principle of measuring digitally the flow velocity of local voids, and discusses the accuracy of this method. It is shown that the spectrum of local void velocities can be determined reliably with digital values.

The measurement errors of void velocity u_g (m/sec) are within about ±9% in cases when the probes have detector head lengths of 0.8~1.0mm, and head diameters of 0.1 mmφ, when the voids have a flow velocity in the range of 0.2 m/sec≤u_g ≤1.2 m/sec and a radius of curvature of void of 2mm≤R≤16mm.     

Chemical State and Deposition Rate of Nickel Ion Deposit Produced on Heated Surface in High Pressure Boiling Water

Nickel ion deposit was produced on a heated rod surface in high pressure boiling water (150–285°C, 0.4–7.0 MPa). The deposit under the same temperature and pressure conditions as those for BWR reactor water (285°C, 7.0 MPa) was identified as NiO by spectrum profile analysis of the NiLα, NiLβ and 9th-order NiKα₁ lines. Deposition rate was obtained from in situ measurements of deposit thickness, by a photoacoustic method, and from chemical analysis of deposit amount. The deposition rate coefficients obtained in temperature and pressure ranges of 150–250°C and 0.4–4.0 MPa were 2 × 10^?3–5 × 10^?2, which were 0.15–0.45 times as large as those of iron crud. This was attributed to a dissolution effect of Ni ion from NiO. The deposition rate coefficient at 285°C, 7.0 MPa was estimated to be 4.4 × 10^?2–1.3 × 10^?1.     

Frictional Pressure Drop for NaK-N2 Two-Phase Flow in Rectangular Cross Section Channel of Large Aspect Ratio

In this paper, the frictional pressure drop in an isothermal liquid metal-gas two-phase flow through a rectangular channel with large width-to-height ratio is treated semiempirically for a NaK-N₂ two-phase flow system.

The frictional pressure drop in the two-phase flow is compared with the following two reference values :

1. The frictional pressure drop in the liquid flowing alone in single phase with the same velocity as that of the liquid in the two-phase mixture.

2. The frictional pressure drop in the liquid flowing alone in single phase with the same mass flow rate as that of the liquid in the two-phase mixture.

The comparison with the former reference value is necessary for the prediction of friction loss in a liquid metal MHD generator channel whose medium would be two-phase mixture.

The semiempirical analysis was performed assuming the two-phase mixture to be a continuous medium with its properties, e.g. viscosity and density, defined by void fraction and the velocity determined by the total mass flow rate.

In the region of low slip and density ratio ρ_g/ρ_l the frictional pressure drop in the two-phase flow appeared to be smaller than that due to the liquid flowing alone with the same velocity as that of the liquid in the two-phase flow.

The experiments have been undertaken with the NaK-N₂ two-phase mixture flowing through a rectangular channel (4 × 60 mm²).

Data were taken over the following parameter range:

NaK velocity: 5～30 m/sec, Void fraction: 0～70%

Density ratio: 0.006～0.013, Quality: 0.07～1.10%.     

Effects of Hydrogen Peroxide on Corrosion of Stainless Steel, (I)

In order to evaluate the effects of hydrogen peroxide (H₂O₂) on intergranular stress corrosion cracking, a high temperature high pressure water loop, which can control H₂O₂ concentration with minimal oxygen (O₂) co-existence, is required. This loop is characterized by

1. A once-through type loop to prevent accumulation of decomposed O₂ in the loop

2. Minimized autoclave volume to prevent bulk thermal decomposition of H₂O₂

3. A polytetrafluoroethylene (PTFE) lining to prevent surface decomposition of H₂O₂, and

4. A H₂O₂ monitoring system with an off-line H₂O₂ detector to determine concentration in the sampled water which is combined with an in-line dissolved O₂ detector to determine the decomposed O₂ concentration.

The authors developed such a loop previously. In the present work, performance tests were carried out and measured data were evaluated by comparing with predicted values to verify whether the target characteristics were met. The measured H₂O₂ remaining in the sampled water agreed with the predicted amount within 5%. It was confirmed that the ratio of H₂O₂ remaining in the loop autoclave was more than 90% and the concentration could be monitored continuously with the in-line dissolved O₂ detector installed after the cooler in the loop. Electrochemical corrosion potential (ECP) and frequency dependent complex impedance were measured successfully by changing H₂O₂ concentration.     

Effect of Operational Pressure on Periodic Oscillation of Secondary Circulation near the Bottom of the Thermal Diffusion Column

A computational code has been developed to analyze the non-steady flow field of the thermal diffusion column in the higher pressure region. Numerical analyses for H₂-HT are performed for the thermal diffusion column with an effective height of 1,500 mm, a hot wire of 0.15 mm and a cold wall of 15 mm in radius. In the condition that temperatures of cold wall and hot wire are 77.35 and 1,277.35 K at the pressure less than 0.112 MPa, the flow fields reach the steady state. However, a secondary circulation observed near the bottom of the column moves periodically at the pressure of 0.112 MPa or more. The frequency of the flow fields becomes larger as the gas pressure increases. The marginal pressure to make flow field apart from the steady state to the periodic state is predicted with the present analyses.     

Densification and Swelling in UO2 Pellets under Hydrostatic Pressure Condition

The effect of hydrostatic pressure on the volume change in unirradiated UO₂ pellets has been examined using an out-of-pile high pressure annealing technique. The pellet volume change was generated by annealing UO₂ pellets at 1,500°C and at higher or lower ambient external pressures of 10–150 MPa Ar/0.2%H₂ gas than the sintering pressures of 50 or 100MPa at 1,800°C. The pressure difference, Δ P, between bubble internal and external hydrostatic pressures during the annealing corresponded to a range of ?101 to 82MPa. The volume change directly depended on the sign and magnitude of Δ P. More negative Δ P caused larger densification due to the shrinkage of the as-sintered bubbles. Almost no volume change was observed at nearly zero Δ P, and fuel swelling due to the bubble growth increased at more positive Δ P. The bubble shrinkage and growth data were analyzed by the rate equation of Hull and Rimmer. The fractional volume changes calculated by the model were in good accordance with the measured values in the wide range of—8 to +10%.     

Void Fraction and Pressure Drop in Liquid Metal Two-Phase Flow

This paper describes a new correlation for predicting a two-phase frictional pressure drop multiplier, and discusses the pressure level effects and the mass velocity effects. This correlation predicts satisfactorily the frictional pressure drop not only for liquid metals but also for ordinary fluid two-phase flow in a wide range of flow variables.

The authors' void fraction correlation previously proposed is also compared with published data of void fraction for liquid metal two-phase flow, and is found to represent well the mass velocity effects. Wettability and magnetohydrodynamic effects are discussed briefly in relation to the hydrodynamic characteristics of liquid metal two-phase flow.     

Pressure Recovery in a Diffuser for Gas Centrifuge

The pressure recovery of supersonic flow at very low density was studied in a vane-island type diffuser for gas centrifuge.

A tester of diffuser with a rapidly rotating cylinder was used in experiments. Wall static pressures were measured at many points in the diffuser to observe the static pressure distribution. The change of pressure distribution with back pressure and the effect of flow rate were investigated. Pressure distribution showed that the pressure recovery occurred in the converging section. The pressure ratio increased linearly with the back pressure in this experimental range and the effect of flow rate was not observed.

A numerical analysis of the pressure recovery in the channel section of the diffuser was made by applying the finite difference method to the slender-channel equations. The pressure distribution obtained in experiments could be explained as a result of supersonic compression with reverse flow.     

Effects of Annealing under High Static Pressure on Precipitation Behavior of Fission Gas Bubbles in Irradiated UO2

Annealing experiments were carried out on irradiated UO₂ in argon gas under high pressure (600 and 1,000 kg/cm²) as well as atmospheric, at temperatures of 1,400°–1,600°C. The effects of high external pressure on the behavior of fission gas bubbles in the irradiated UO₂ were studied by comparing replica electron micrographs of fractured surfaces of specimens annealed under different temperatures and pressures. The results indicate that high pressures such as above 600 kg/cm² can be effective in surpressing the growth of fission gas bubbles in both intergranular and intragranular zones, and in inhibiting the joining together of intergranular bubbles to form direct passages for fission gas release.     

Incipient Boiling Pressure Pulse of Sodium under Forced Convection by Direct Heating

An account is given of experiments on incipient boiling pressure pulses imparted by liquid sodium, performed in a forced convection loop. The sodium is heated by direct current applied to the liquid metal itself in a vertical tube of 14.9 mm inner diameter through which the medium pumped. The experiments were carried out with the following ranges:

Input power: 6–12kW,Pressure at condenser: 0.6–1.0 kg/cm², Inlet temperature: 780^°–850^°C, Flow rate: 1.0–3. 5 l/min

Typical pressure pulses registered during incipient boiling presented the form of damped oscillation. The initial pressure pulses were dependent on the location of boiling inception along the test section, the incipient boiling pattern and the degree of superheat. The initial pressure pulses observed were in the range of 0–3. 5 kg/cm². The pressure pulses increased with the degree of superheat, which ranged 0^°–150°C.

The magnitudes of pressure pulses exceeded the saturation vapor pressure corresponding to the temperature of superheated liquid. Consideration of a simplified model indicated that, during incipient boiling, the pressure in the vapor phase oscillates while approaching asymptotically the saturation pressure.     

Effects of Flow Circulation on Hot-Wire Temperature at Top and Bottom of Thermal Diffusion Column for Isotope Separation

Abstract

By using the two-dimensional rigorous numerical solution of equations of change, the change in hot-wire temperature caused by flow circulation near the top and bottom plates of thermal diffusion column with 14.7 mm-radius and 80 K cold-wall was analyzed with constant heat flux condition on hot-wire temperature boundary by parametrically changing the pressure. Flow field analysis for H²-HD (tracer level) gas mixture in total-reflux operation has revealed : (i) The magnitude of the change in hot-wire temperature is almost proportional to the square of the pressure, while the magnitude of the free convection is almost proportional to the pressure. (ii) The magnitude of the change in hot-wire temperature at the bottom is larger than that near the top plate, while the magnitude of the radial flow component is almost the same at the top and bottom, and (iii) The range of temperature change is wider than the range at the top and bottom part of the column where convective flow turns around (i.e. radial velocity components significantly exist).     

Structure of Flow Fields in Low Pressure Impactor

In order to clarify the detailed flow fields of impinging jets in a low pressure impactor, nitrogen and argon flow fields are investigated experimentally and numerically at a relatively small range of P _down/P _up, where P _down is the downstream stagnation pressure and P _up the upstream stagnation pressure. The pressure at the center of collection plate, P _c, is measured in addition to the flow visualization by Laser Induced Fluorescence (LIF) technique, which is used in previous study. Furthermore, the flow fields in a low pressure impactor have been simulated by solving the axisymmetric Euler equation through Harten-Yee TVD method. The effects of P _down/P _up and H/D on flow fields are examined in detail, where H is the jet-to-plate distance and D the nozzle diameter. The calculated shock wave position on jet axis and the pressure at the center of collection plate are in reasonable agreement with the experimental results. It is found that the structure of flow fields changes drastically at a certain value of P _down/P _up and there exist hysteresis phenomena in the relationship between the value of P _c/P _up and that of P _dowb/P _up for both gases. The formation of the separation bubble at a certain value of H/D is discussed.     

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.     

Effect of Argon Ion Sputtering of Surface on Hydrogen Permeation through Vanadium, (II) Effect of Sputtering of Both Side Surfaces

As part of studies on plasma-wall interactions of fusion reactors, the effect of Ar ion sputtering of both the upstream side and the downstream side surfaces of a V coupon upon its H₂ permeability has been studied. The H₂ permeability measuring apparatus has been modified to install another ion gun for the use in sputtering the downstream side specimen surface. The H₂ permeation rates were measured at 673K by changing the H₂ pressure and sputtering mode. The downstream side sputtering has been observed to enhance the H₂ permeability, though its degree was smaller than that due to the upstream side sputtering. The both side sputtering resulted in the largest H₂ permeability value ever obtained for V. The rate of H₂ permeation through V seemed to be determined by the surface processes including the downstream side rather than the bulk diffusion even after the both side sputtering. Based on AES measurements, the enhancement of H₂ permeability caused by sputtering was attributed to the diminishing of the surface O impurity.     

Control of Oxygen Partial Pressure with Stabilized Zirconia Cell

A study was made on the method of controlling oxygen partial pressure in the range of 10^?4~10^?8 atm by the addition of oxygen into purified argon gas through stabilized zirconia cell. The oxygen partial pressures obtained by controlling the electric current passed through the cell and the feed rate of the carrier gas were found to agree well with theoretical values in the range of 10^?4 to 10^?6 atm oxygen partial pressure. Below 10^?6 atm, however, some discrepancy appeared between the theoretical and observed values, due to the oxygen partial pressure being reduced by the reaction with impurity gases such as hydrogen present in the argon. A discussion is also presented on the measured polarization curves for the anode and cathode of the stabilized zirconia cell.     

Experimental Study of Counter-Current Two-Phase Flow in Horizontal Tube Connected to Inclined Riser

In order to determine the Counter-Current Flow Limitation (CCFL) in hot legs of PWRS, CCFL characteristics of air-water and saturated steam-water flow were experimentally investigated in a modeled flow path of a horizontal tube connected to an inclined riser. The ranges of dimensions of experimental tubes were as follows: diameter D 0.026–0.076 m, length of horizontal tube H 0.01–0.4 m, length of inclined riser I 0.038–0.6 m and inclination angle of inclined riser θ 40° or 45°.

Wallis-type correlation (J _g ^*1/2+mJ _i ^*1/2=C) was applicable to the data during a steady separated flow. An analysis based on envelope theory showed that the constant C should be a function of H/D and I. A function of C with those parameters was empirically determined by using data obtained in this study. The developed function correlated well with the results of Richter et al. (D = 0.203 m, H = 1.26 m, I = 0.5 m and θ = 45°). The constant m in the Wallis-type correlation was almost constant 0.75. The problems were discussed, which should be made clear to apply the correlation obtained in this study to an actual PWR hot leg.     

Corrosion behavior of TiO2-treated type 304 stainless steels in high temperature water containing with hydrogen peroxide

ABSTRACT

Titanium dioxide (TiO₂) treatment coupled with ultraviolet irradiation was selected as a corrosion mitigation technique for Type 304 stainless steel (SS) in high-temperature pure water with the presence of hydrogen peroxide (H₂O₂). Type 304 SS specimens were pre-oxidized in oxygenated pure water at 288 °C and then coated with TiO₂ nanoparticles by hydrothermal deposition. Electrochemical polarization analyses were conducted to investigate the corrosion behavior of both TiO₂-treated and pre-oxidized specimens in 288 °C pure water with 300 ppb H₂O₂. Ultraviolet (UV) irradiation was then imposed upon the TiO₂-treated specimens to examine if there was any distinct photoelectric effect on the corrosion behavior of the treated samples. It was found that the electrochemical corrosion potentials of the TiO₂ treated specimens under UV irradiation were 10–20 mV lower than those without UV. In addition, the corrosion current densities of the treated specimens were also lower in the presence of UV radiation. Without UV radiation, however, no significant differences were observed between the TiO₂ treated and untreated specimens. These results indicate that the TiO₂ treatment in combination with UV radiation would reduce the corrosion rate of Type 304 SS in H₂O₂-rich, high-temperature pure water.     

Release of Neptunium from Neptunium-Doped Borosilicate Waste Glass

The release of neptunium from a neptunium-doped borosilicate waste glass was studied at 90°C in deionized water and silicate water. The standard MCC-1 static leach method was applied to the tests for durations up to 91 days with the SA/V ratio of 10 m^?1.

The normalized elemental mass loss obtained for neptunium was about 5 g/m² for both the deionized and the silicate water leachates. This value is similar to those for currently typical borosilicate waste glasses. That is, the studied glass is comparable with the typical glasses in terms of the ability to immobilize neptunium.

The time dependence of the release of neptunium from the glass was different from those of soluble glass components such as sodium, boron and cesium, but similar to that of strontium. A part of neptunium, like strontium, probably remained in the surface layer formed on the leached glass. The neptunium species in the surface layer was predicted to be NpO₂.xH₂O(am) based on available solubility data.