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.     

Oxidation behaviour of fecralloy and 20/25/Nb stainless steels and a nickel-based alloy,PE16, in argon containing 7 μatm water vapour and 375 μatm hydrogen

The oxidation behaviour of four alloys [yttrium-bearing and yttrium-free Fecralloy ferritic stainless steels, a 20/25/Nb austenitic stainless steel and a nimonic alloy, PE16] have been studied in argon (1.3 atm pressure) containing 7 μatm water vapour and 375 μatm hydrogen. The alloys were exposed for periods up to 7166 h at temperatures in the range, 650–1000 °C. The overall reaction kinetics were determined, as were the magnitudes and nature of both the general and any internal attack. The behaviour of the alloys in wet argon was consistent with that observed in fully oxidising environments, except at the highest temperature studied, 800 and 1000°C, with the 20/25/Nb and Fecralloy steels respectively. In carbon dioxide a greater attack of both alloys and a more complex composition of the oxide film on the 20/25/Nb steel have been attributed to its higher oxygen potential compared with that of the H₂O/H₂ gas mixture.     

Simulation Procedure for Multistage Water/Hydrogen Exchange Column for Heavy Water Enrichment Accounting for Catalytic and Scrubbing Efficiencies

The present paper gives a simulation procedure for multistage water/hydrogen exchange columns for heavy water enrichment using hydrophobic catalysts. The Murphree-type efficiencies for H₂O, HDO and D₂O are used as the scrubbing efficiencies for sieve trays. The reaction rate of H₂+D₂?HD is assumed to be very rapid and equilibrated at the outlet of the catalyst bed. The catalytic efficiencies defined for H₂O(g) and D₂O(g) are considered for the nonequilibrated exchange reactions: H₂+HDO(g)?HD+H₂O(g) and H₂+D₂O(g)?D₂+H₂O(g). Those efficiencies are treated as input variables for the simulation. The main calculational loop is based on the Newton-Raphson iteration, but the order of the Jacobian matrix is just equal to the number of sieve trays for vapor/hydrogen scrubbing. The procedure is applicable to solution of operating problems in a wide range of input and output specifications.     

Removal of Tritiated Water Vapor by Adsorption

Abstract

Experiments were conducted on the dynamic adsorption of tritiated water vapor, using a column packed with either silica-gel, activated alumina, or molecular sieve 5A. The column was 4 mm I.D. and 5–30 cm long. The runs were performed at 30°–70°C. Tritiated water vapor (HTO) was loaded into the column with a concentration of 170 μμCi/ml, either in pulses of predetermined duration or continuously (breakthrough). The concentrations of H₂O and HTO at column outlet were measured. Particular interest was attached to observing the effect of differences in the pretreatment applied to the adsorbents (whether dried or saturated with water), and in the H₂O partial pressure of the carrier gas. It was found that the adsorption characteristics shown for HTO were not influenced to any appreciable extent by differences in the pretreatment applied to the adsorbents. On the other hand, adsorbent performance depended sensitively on the H₂O pressure in the carrier gas.

Adsorption models for a two-component mixture composed of H₂O and HTO were sought for describing the adsorption mechanism. For the particular case of the molecular sieve 5A, the Langmuir-type mixed adsorption model was found to give values agreeing fairly well with experiment. A model postulating chemisorption of H₂O into hydroxyl group on the adsorbent surface, to be subsequently replaced by tritium, was found suitable for explaining the adsorbent behavior in the case of silica-gel.     

Simulation of the inhibition of water α-radiolysis via H2 addition

The continuous formation of H₂, O₂, and H₂O₂ observed in water during α-radiolysis may be suppressed by the addition of H₂ above the threshold hydrogen concentration (THC). Using the FACSIMILE simulation code, water radiolysis was reproduced in order to determine the THC and clarify the mechanism at room temperature. Using the reaction set and rate constants reported by Ershov and Gordeev together with the primary yields for water decomposition products generated using 12 MeV α-particles, the THC was found to be 165 μM. Further simulation results clearly showed that the value of THC is strongly dependent on the reaction set and rate constants. In addition, a possible mechanism involving a chain reaction governed by the two reactions OH + H₂ → H + H₂O and H + H₂O₂ → OH + H₂O was proposed. Furthermore, the same inhibition effect was found when a high-temperature simulation (300 °C) was performed, but the concentration range and THC were much smaller than the values obtained at room temperature. The importance of the reverse reaction OH + H₂ → H + H₂O was also investigated.     

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.     

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.     

Reaction rate of Na-based titanium nanofluid with water

Suppression of chemical reactivity in reaction between sodium (Na) and water by Na-based titanium nanofluid (NaTiNF) was verified by measuring the difference between the H₂ generation rates of NaTiNF–water reaction and sodium–water reaction (SWR). H₂ generation at the beginning of the reaction was slower in NaTiNF–water reaction than in SWR. To determine the effect of temperature on the reaction rate, NaTiNF–water reactions were conducted at 104 °C, 120 °C and 150 °C. At 104 °C, the reaction rate of SWR was twice as fast as NaTiNF–water reaction. This result demonstrates that the chemical reactivity of liquid Na is suppressed by the presence of Ti nanoparticles in liquid Na. The reaction rate of NaTiNF–water reaction increased with reaction temperature. The activation energy of NaTiNF–water reaction was obtained using the Arrhenius equation.     

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.     

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.     

Hydrogen Isotope Separation by Plasma-Chemical Method

Deuterium transfer (exchange) reaction as shown in HDO+H₂=H₂O+HD was studied as a case similar to the tritium transfer reaction as shown in DTO+D₂=D₂O+DT, the first step in tritium isotope separation of the tritiated heavy water DTO. The transfer reaction was plasma-chemically catalyzed by allowing a gas mixture such as H₂O/D₂, D₂O/H₂, H₂O/HDO/H₂ or H₂O/D₂O/HDO/H₂ to flow through an atmospheric pressure discharge zone formed in a reaction chamber, the inner temperature of which was maintained just above 100°C. The plasma-chemical reactions diagnosed by infrared and emission spectroscopy revealed that the mixture underwent instantaneous deuterium transfer reactions as it passed the zone. The effectiveness of the method was demonstrated by high deuterium transfer rate, high separation factor of the transfer and a possibility of miniaturizing the separation facility.     

Verification of hydrogen isotope separation by pressure swing adsorption process: Successive volume reduction of isotopic gas mixture using SZ-5A column

For the purpose of verifying the applicability of pressure swing adsorption (PSA) process to such as volume reduction of tritiated waste storage, an experimental series was carried out by a PSA apparatus having a zeolite packed column operated at the liquefied nitrogen temperature, where synthetic zeolite 5A was used as a candidate of adsorbents. Experimental results are shown here which were obtained from cyclic operation of isolating a volume of hydrogen decontaminated with its heaver isotope from a mixture of H₂ and D₂ while reducing a volume of this mixture storage. Successive reduction during six cycles is observed in the inventory of this hydrogen mixture in a gas holder. Experimental data are analyzed in order to evaluate the performance of this PSA process operating the hydrogen isotope separation, where several factors are introduced defining efficiencies of decontamination, volumetric reduction, and so on. These factors suggest that the PSA process is available for successive reduction of a tritiated hydrogen storage inventory. A tritium waste management system of PSA process combined with electrolysis is considerable which is aiming at reducing the inventory of tritiated water in storage.     

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.     

Decomposition pressures in the (α + β) fields of the Li-LiH,Li-LiD,and Li-LiT systems

Decomposition (“plateau”) pressures of H₂, D₂, and T₂ over Li-LiH, Li-LiD, and Li-LiT alloys were determined between 600 and 850°C, for pressures ranging from 3 to 460 Torr, and for alloy compositions falling within the (α + β) miscibility gaps. The measurements were carried out separately for each hydrogen isotope using the same lithium sample and experimental procedures. For each system the ln P vs. 1/T data form a pair of linear segments, the intersection of which represents the monotectic temperature (694°C for Li-LiH, 690°C for Li-LiD, and 688°C for Li-LiT). For a given temperature plateau pressures were in the order P_T2 >P_D2 >P_H2. The $\text{D}\text{H}$ and $\text{T}\text{H}$ isotope effects in pressures varied from 1.48 and 1.74 at 600°C to 1.34 and 1.45 at 850°C. The results were used to calculate the standard free energies of formation of solid LiH, LiD, and LiT. The tritium gas used in this study had significant amounts of hydrogen and deuterium. A method for correcting the plateau pressures of this mixture to those of pure tritium is presented.     

水-氢交换氢同位素体系HD/H_2O、DT/D_2O和HT/H_2O分离性能模拟研究

计算模拟应用于氢同位素分离领域,能够方便、快捷地进行工艺条件分析。本工作采用数值模拟的方法对比研究了水-氢催化交换过程中HD/H_2O、DT/D2O和HT/H_2O三种氢同位素体系的分离性能。研究表明:在一定工艺条件下,三种体系均在操作温度为343K时达到最大的分离效果;随着气液比从1.0增大到3.0,最优操作温度均从343K降低到323K,但是在此过程中,HT/H_2O体系的分离效果受温度的影响较小一些;在达到最大分离效果的目标下,HT/H_2O体系需要的理论塔板数比HD/H_2O和DT/D2O体系少,同时,在优化的工艺条件下,三体系气相中氢同位素浓度在交换柱内分布曲线存在一定的差异。     

Three Phase Region in Ternary System UO2-PUO2-PU2O3

The thermal decomposition of PuF₆ in the temperature range from 100° to 160°C was studied. At 100° and 120°C, no decomposition was detected. At 140° and 160°C, the rate of decomposition during reaction lasting up to 20 hr, and the dependence of the decomposition on the initial PuF₆ pressure were determined. The results are explained by assuming that the rate of decomposition is proportional to the 0.4-th power of PuF₆ pressure. The activation energy of the reaction was found from calculation to be 14.8 kcal/mole.     

Chromatographic Study on Boron Isotopic Fractionation at High Pressure

Boron isotopic fractionation factor (S) between boron adsorbed onto kaolin clay and boron in aqueous solution was determined by break-through column chromatography at 25.0 MPa at 5 and 25°C. The S values obtained were 1.0021 at 5°C and 1.0011 at 25°C, and were smaller than those obtained by the batch method performed at the atmospheric pressure at room temperature. Theoretical calculations estimate that more than 90% of boron in the clay phase was taken up as B(OH)₃-form at high pressures. Combining the present S values with preliminarily obtained one at 12.0 MPa, it is likely that S value decreases with increasing pressure, which suggests that the difference of the partial isotopic molar volumes between ¹⁰B(OH)₃ and ¹¹B(OH)³ is larger than that of the volumes between ¹⁰B(OH)₄ ^? and ¹¹B(OH)₄ ^?.     

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.