Application of a boron doped diamond (BDD) electrode as an anode for the electrolytic reduction of UO2 in Li2O–LiCl–KCl molten salt

A boron doped diamond thin film electrode was employed as an inert anode to replace a platinum electrode in a conventional electrolytic reduction process for UO₂ reduction in Li₂O–LiCl molten salt at 650 °C. The molten salt was changed into Li₂O–LiCl–KCl to decrease the operation temperature to 550 °C at which the boron doped diamond was chemically stable. The potential for oxygen evolution on the boron doped diamond electrode was determined to be approximately 2.2 V vs. a Li–Pb reference electrode whereas that for Li deposition was around ?0.58 V. The density of the anodic current was low compared to that of the cathodic current. Thus the potential of the cathode might not reach the potential for Li deposition if the surface area of the cathode is too wide compared to that of the anode. Therefore, the ratio of the surface areas of the cathode and anode should be precisely controlled. Because the reduction of UO₂ is dependent on the reaction with Li, the deposition of Li is a prerequisite in the reduction process. In a consecutive reduction run, it was proved that the boron doped diamond could be employed as an inert anode.     

Isotope Effects in Electrolytic Formation of Lithium Amalgam

Isotope effects in the lithium amalgam formation were studied by using the mercury cathode and LiOH solutions. The electrolyses were carried out at different conditions of both applied voltages 4–10 V, and the concentrations of initially charged LiOH, 0.5–5 mol/dm³. Higher efficiency of electrolytic amalgam formation was observed at higher LiOH concentrations and higher applied voltages. At these conditions, however, significant amount of solid amalgam was produced in the mercury phase. From the isotopic analyses on the samples taken during the electrolyses, it was found that the isotopic equilibrium was attained between the aqueous and the liquid amalgam phases. The isotopic equilibrium constant (isotope separation factor) was determined as 1.056 (average value for all the experiments) at 20°C.     

Nuclear and thermal effects during electrolytic reduction of deuterium at palladium cathode

In a galvanostatic experiment of charging deuterium in a palladium cathode, nuclear and thermal effects were found. A sintered palladium electrode shaped as parallelepiped was used. After 6 days of electolysis at 200 mA/cm², a simultaneous emission of neutrons, tritium excess in the electrolytic solution, and temperature rapid increase was observed. During the event which lasted 4 minutes, we counted 7.2×10⁵ neutrons while the electrode temperature reached 150°C. Electrochemical procedure for charging the palladium electrode by deuterium using galvanostatic pulses as well as the associated electrode temperature trends are shown.     

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.     

Effects of water chemistry and potential distribution on electrochemical corrosion potential measurements in 553 K pure water

The effects of water chemistry distribution on the potential of a reference electrode and of the potential distribution on the measured potential should be known qualitatively to obtain accurate electrochemical corrosion potential (ECP) data in BWRs. First, the effects of oxygen on a platinum reference electrode were studied in 553 K pure water containing dissolved hydrogen (DH) concentration of 26–105 μg kg^?1 (ppb). The platinum electrode worked in the same way as the theoretical hydrogen electrode under the condition that the molar ratio of DH to dissolved oxygen (DO) was more than 10 and that DO was less than 100 ppb. Second, the effects of potential distribution on the measured potential were studied by using the ECP measurement part without platinum deposition on the surfaces connected to another ECP measurement part with platinum deposition on the surfaces in 553 K pure water containing 100–130 ppb of DH or 100–130 ppb of DH plus 400 ppb of hydrogen peroxide. Measured potentials for each ECP measurement part were in good agreement with literature data for each surface condition. The lead wire connecting point did not affect the measured potential. Potential should be measured at the nearest point from the reference electrode in which case it will be not affected by either the potential distribution or the connection point of the lead wire in pure water.     

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.     

Characteristic of Two-phase Slanting Flow in Rod Bundle

Palladium membrane has been studied for sepration and purification of hydrogen isotopes because of its large permeability. In order to consider permeation of mixture of hydrogen isotopes, solubilities of protium and deuterium in palladium were studied in the temperature range of room temperature to 500°C using breakthrough method. It was observed that solubilities were represented by Sieverts' law and that the separation factor of protium-deuterium binary system was different from the isotope effect ratio. The ideal adsorbed solution theory by Myers and Prausnitz can be applied to estimate the separation factor of protium-deuterium binary system in palladium using the isotope effect ratio observed when protium and deuterium are handled independently. The permeation behavior of multi component hydrogen isotopes through palladium membrane is discussed applying observation on solubilities of this work.     

The Influence of Dissolved Hydrogen on the Corrosion of Type 304 Stainless Steels Treated with Inhibitive Chemicals in High Temperature Pure Water

In order to assess the influence of dissolved hydrogen on the intergranular stress corrosion cracking (IGSCC) characteristics of Type 304 stainless steels treated with inhibitive chemicals, electrochemical corrosion potential (ECP) measurements and slow strain rate tensile (SSRT) tests were conducted in high temperature pure water. A number of thermally sensitized specimens were prepared and then pre-oxidized in a 288°C pure water environment with the presence of 300ppb dissolved oxygen for 360h. Most of the specimens were then separately treated with various inhibitive chemicals including powdered zirconium oxide (ZrO₂), powdered titanium oxide (TiO₂), and zirconyl nitrate [ZrO(NO₃)₂] via hydrothermal deposition at 150°C. Test environments with a dissolved oxygen concentration of 300ppb and various dissolved hydrogen concentrations at 288°C were created. Test results showed that the ECPs of the treated specimens were lower than that of the untreated one no matter what the dissolved hydrogen concentration was. In addition, IGSCC was observed on all specimens (treated or untreated) in all tested environments. However, the untreated specimen exhibited lower elongation, shorter failure time, and more secondary cracks on the lateral surfaces. It was therefore suggested that inhibitive chemicals such as ZrO₂, TiO₂, and ZrO(NO₂)₂ did provide a certain degree of enhancement in improving the mechanical behavior of the treated specimens and in prolonging IGSCC initiation times.     

Electrolytic Reduction of Spent Light Water Reactor Fuel Bench-Scale Experiment Results

A series of experiments were performed to demonstrate the electrolytic reduction of spent light water reactor fuel at bench-scale in a hot cell at the Idaho National Laboratory Materials and Fuels Complex. The process involves the conversion of oxide fuel to metal by electrolytic means, which would then enable subsequent separation and recovery of actinides via existing electrometallurgical technologies, i.e., electrorefining. Four electrolytic reduction runs were performed at bench scale using ～500 ml of molten LiCl–1 wt% Li₂O electrolyte at 650°C. In each run, ～50 g of crushed spent oxide fuel was loaded into a permeable stainless steel basket and immersed into the electrolyte as the cathode. A spiral wound platinumwire was immersed into the electrolyte as the anode. When a controlled electric current was conducted through the anode and cathode, the oxide fuel was reduced to metal in the basket and oxygen gas was evolved at the anode. Salt samples were extracted before and after each electrolytic reduction run and analyzed for fuel and fission product constituents. The fuel baskets following each run were sectioned and the fuel was sampled, revealing an extent of uranium oxide reduction in excess of 98%.     

双柱周期逆流法分离氢同位素

将具有正、反氢同位素效应的2种贮氢材料Pd和LaNi_4.7Al_0.3结合,组成双分离柱,测试了原料气氘原子摩尔分数为0.5和0.1的2种混合气体的流出曲线,并进行了周期逆流方式的分离实验。实验结果表明,该分离方法具有较高的分离效率,产品气的氘原子摩尔分数一般大于0.995。改进方式后分离氘原子摩尔分数为0.1的原料气,产品气的最大氘原子摩尔分数为0.998,最大氘富集比为9.98,氘的回收率为92.5%,尾气中氢原子摩尔分数大于0.996,全分离因子大于120 000。     

Enrichment and Volume Reduction of Tritiated Water Using Electrolysis Cell Having Hydrogen Permeable Cathode

The electrolysis rate and the separation factor for hydrogen isotopes are measured using the electrolysis cell having the hydrogen permeable cathode. As the hydrogen gas without the vapor of electrolyte is obtained by this method, decrease of the apparent separation factor by mixing with vapor can be avoided. It is also observed in this study that enrichment and volume reduction of tritiated water using the bipolar electrode electrolysis cell is effective because it gives small loss of tritium from the cell during volume reduction. The separation factor obtained in this study indicates that attachment of two or three sub-cells is enough for volume reduction of tritiated water.     

Observation of Lithium Isotope Effect Accompanying Electrochemical Insertion of Lithium into Tin

Electrolysis of an organic electrolyte solution containing lithium ions was conducted to observe lithium isotope fractionation accompanying electrochemical insertion of lithium from the electrolyte to tin metal. The experimental setup consisted of a three-electrode electrolysis cell with a tin wire as cathode, lithium foils as anode and reference electrode and 1 M LiPF₆ dissolved in 1:2 volume ratio of ethylene carbonate and methylethyl carbonate as electrolyte and a power supply. The supplied electric energy was mostly consumed for the lithium insertion from the electrolyte to the tin cathode within the range of the cathode potential, relative to the reference electrode potential, from 0.05 V to 0.30 V. The single-stage separation factor increased with increasing cathode potential and seemed to asymptotically approach to the limiting value of 1.015 at 25®C, with ⁶Li being preferentially fractionated into tin metal.     

电解-精馏级联分离H2／HD过程的理论分析

为研究电解精馏级联氢同位素分离过程的规律性,建立了电解-精馏级联的微分模型,计算了H2／HD系统的分离行为,并获得了电解和精馏过程中系统的浓集行为,即,电解池中HDO摩尔分数从2．88×10^-4增长到8．35×10^-4精馏柱再沸器中HD摩尔分数达到0．033。随时间的延长,脱氘率下降,在精馏柱上HD的摩尔分数整体抬升。进一步研究了回流比对脱氘率的影响,结果显示,回流比为3～7时,平均脱氘率可达0．9828～0．9973。实验结果表明,电解-精馏级联分离氢同位素有明显的浓集效应。     

低温循环色谱法分离H_2/HD

低温循环色谱法(CCC)是一种有效的氢同位素分离方式。在升级改造后的低温色谱分离装置上开展了H2/HD体系的分离研究。结果表明:原始氘丰度为1.4×10-4的高纯氢经过CCC 4个流程后,氘丰度达到1.173×10-3;为获得最佳色谱柱柱效,CCC的进样量控制在组分峰的容量因子下降10%时较为合适;CCC的双柱间可互相充当解吸柱与接收柱的角色,在柱结构与程序升温条件相同的前提下,双柱间分离效果的差异可能是进样点的选择和进样压力的不同造成的,与进样时间无关。     

Extraction of hydrogen into vacuum by electrochemical hydrogen pump for hydrogen isotope recovery

For hydrogen isotope recovery, an electrochemical hydrogen pump using CaZr_0.9In_0.1O_3?α under vacuum in the cathode compartment has been proposed. Two types of electrodes—pasted and electroless plated electrodes—were used to evaluate the mass transfer process. When the hydrogen pump was operated using direct current, the voltage between electrodes under vacuum was less than that under atmospheric pressure, regardless of electrode type. This result indicates that the hydrogen pump performance is improved under vacuum. In the case of the pasted electrode, however, the voltage decrease was larger than that in the case of the plated electrode. Electrochemical impedance spectroscopy revealed that the diffusivity in the pasted electrode was smaller under atmospheric pressure than under vacuum. From comparing the microstructures of the two electrode types, the pasted electrode has larger pores and would be more suitable for the hydrogen pump under vacuum.     

Observation of H/D isotope effects on polymer electrolyte membrane fuel cell operations

The hydrogen isotope effects upon operation of a polymer electrolyte membrane fuel cell have been observed. The deuterium concentration in the exhaust hydrogen gas from the cell was found lower than that of the hydrogen gas fed to the cell, which indicated that the heavier isotope of hydrogen was preferentially oxidized at the anode. The overall hydrogen isotopic separation factor between the oxidized and non-oxidized hydrogen ranged from 3.46 to 3.99 and increased with decreasing flow rate of the feed gas or increasing rate of hydrogen utilization.     

REDOX Decontamination Technique Development, (I)

The decontamination technique is required to have a high decontamination rate and decontamination factor, to apply to irregularly formed metallic waste, and minimize secondary waste volume for component replacement and decommissioning. The authors were developed a new decontamination technique using Ce⁴⁺ for decommissioning, which was named “REDOX decontamination technique”. This paper has investigated decontamination conditions and regeneration conditions in a non-radioactive (namely cold) fundamental test. The decontamination conditions, namely dissolution conditions for stainless steel and carbon steel were selected using simulated samples in nitric acid solutions in varying Ce⁴⁺ concentrations, HNO₃ concentration, temperatures, and linear flow rate of decontamination solutions. The regeneration conditions for decontamination reagent were selected in various electrode materials and varying electrode separation distance, anode area/cathode area ratio, current density, Ce³⁺ concentration, and HNO₃ concentration. The REDOX decontamination technique was ascertained to have a high dissolution rate and the decontamination reagent was ascertained to be regenerated effectively by electrolysis.     

钯合金膜分离器级联氢同位素分离研究

提出了一种基于钯合金膜分离器串联(PMSCS)的氢同位素分离系统的初步设计,建立了评估该分离方法分离效果的数学模型,根据此模型和前期关于分离器分离系数的测定结果,估算了多级氢同位素分离系统分离级数与分离产品气、尾气中氘和氕之间的关系.结果表明,分离系统所串联的分离级数量越大分离效果越好.对于一个5级串联分离系统(单级分离器分离系数q=1.8),当以50%H-50%D混合气体为原料气时,若产品气的提取比例为40%,产品气中的D含量将达到约92%,产品气得到了充分富集;若尾气的提取比例为40%,尾气中的氢含量将达到约99.95%,尾气中的氘得到了充分的贫化.与低温蒸馏、热循环吸附分离和钯合金膜分离器级联分离比较,钯合金膜分离器串联系统具有结构简单、氚的贮留量小等优点,适用于氢同位素混合气体的分批次操作分离.     

Fast Transport of Colloidal Particles through Quartz-Packed Columns

Abstract

The migration of polystyrene latex particles (diameter = 310, 170 and 40 nm) through columns packed with 30 um quartz powder was experimentally studied at low eluant velocity at pH 6.0 + 0.1. The average velocity of polystyrene latex particle was found to be larger than that of HTO. The ratio (separation factor) of the average velocity of polystyrene latex particle to that of HTO increased with increasing the size of polystyrene latex particle and with decreasing the concentration of sodium chloride added under the experimental conditions. This reveals that the colloid migration process in the geological media is similar to that occurring in hydrodynamic chromatography. A model proposed for hydrodynamic chromatography was used to calculate the separation factor in which the potentials from the double layer force and from the van der Waals force were taken into account. The separation factor, calculated with the model by using the measured surface potentials of polystyrene latex particle and quartz powder and by using Hamaker constant evaluated from the literature, was found to agree well with the experimental result.     

Electrolytic dissolution characteristics of SIMFUEL in carbonate solutions of high concentration

This work studied anodic dissolution characteristics of a SIMFUEL electrode at several potentials in carbonate solutions of a high concentration at several pHs. The electrolytic uranium dissolution of SIMFUEL was much affected by a corrosion product of UO₂CO₃ generated at the electrode during the dissolution in carbonate solution. The corrosion product distorted the voltammogram of SIMFUEL in the potential region of oxygen evolution and increased the overpotential of oxygen evolution at the electrode. The effective dissolution of the SIMFUEL electrode in a carbonate solution could be obtained at an applied potential such as +4 V (vs SSE) or more which had an overpotential of oxygen evolution high enough to rupture the corrosion product on the electrode surface. The corrosion potential of SIMFUEL decreased with pH in the carbonate solution, and the dissolution rate and current efficiency of the SIMFUEL increased with a decrease of pH in the carbonate solution.