Combined Electrolysis And Catalytic Exchange Research Articles

Advanced modular system for tritium separation by CECE type process

The main source of tritium is fission reactors PHWR (CANDU) or molten salt (MSR), nuclear fusion reactors (JET, ITER, DEMO) which, in operation, generate significant amounts of tritiated light water or tritiated heavy water, whose efficient processing, through an advanced technology, would contribute to the reduction of stocks and the recovery of tritium and deuterium.The research presented in this work aims to promote a modern management of tritium and its associated materials, by developing a technology for separating hydrogen isotopes through the CECE (Combined Electrolysis and Catalytic Exchange) separation process, for the concentration of tritium in liquid state (HTO, DTO).The conceptual diagram of the Advanced Modular System (AMS), the main component elements, together with the description of 3 modes of experimentation will be presented.The technological process that takes place within AMS is electrolysis of process water and, respectively, isotopic exchange on mixed catalytic packing.

Deuterium Stream Management Leaving the LPCE Column in a CECE Process for Heavy Water Detritiation

In heavy water detritiation using the combined electrolysis and catalytic exchange (CECE) process, deuterium leaving the electrolyzer is fed to the bottom of the liquid-phase catalytic exchange column (LPCE) in which tritium exchanges between the tritiated deuterium gas (moving upward in the LPCE column) and D2O liquid (moving downward in the LPCE column). Once the deuterium gas leaves the LPCE column, typically a trickle bed recombiner (TBR) is used to convert the incoming deuterium gas into the heavy water. In this study a different approach is presented in which instead of using a TBR, an additional LPCE column is used. In the additional LPCE column, deuterium gas is scrubbed with demineralized light water. This process alternative has many advantages over using a TBR. First, the oxidation of isotopic hydrogen is highly exothermic and requires a separate water-cooling circuit to maintain the temperature within the TBR. Second, a TBR requires a relatively complex internal design to ensure proper distribution of the gas, otherwise catalyst burnup may occur. Using a LPCE column instead of a TBR eliminates these complications. This paper presents a high-level layout of the process plant in which a LPCE column is used instead of a TBR. Column modeling and results are also presented.

Comparison of AWD to CECE for ITER-Scale Water Detritiation

Tritium is used as a fuel in nuclear fusion, and water detritiation is an important part of the overall fusion fuel cycle. This paper compares two competing technologies for an ITER-scale water detritiation reactor, namely, the advanced water distillation (AWD) and combined electrolysis and catalytic exchange (CECE) processes. The processes are compared in terms of equipment size and footprint, energy demand, isotope separation characteristics, safety, and technology readiness level. An important technical concern discussed is management of deuterium accumulation since deuterium is enriched along with tritium and D-T separation is inherently more difficult than H-T separation. Interfacing with a downstream isotope separation system is also discussed.

Oxygen Stream Management in a CECE Process

In the combined electrolysis and catalytic exchange (CECE) process, the electrolyzer produces both hydrogen and oxygen streams. Hydrogen is typically fed to the bottom of the liquid-phase catalytic exchange column. The oxygen stream, however, is processed and afterward is either fed back to the trickle bed recombiner in heavy water detritiation or released to the exhaust stack in light water detritiation. This paper discusses the handling of the oxygen stream both in heavy and light water detritiation CECE processes. Oxygen leaving the electrolyzer has a trace amount of tritium gas in it as well as water vapor (due to diffusion across the membrane). Trace tritium is converted to vapor using a catalytic converter and then either scrubbed using an oxygen vapor scrubber or captured in a dryer bed. This study analyzes and compares the different options for handling the oxygen stream in a CECE process.

Modeling and experimental investigation for development of Combined Electrolysis and Catalytic Exchange process for hydrogen isotope separation

A process based on the Combined Electrolysis and Catalytic Exchange (CECE) has been developed for separation of hydrogen isotopes. Indigenously developed Platinum supported on Carbon Aerogel based hydrophobic catalyst was used for hydrogen-water isotope exchange reaction combined with hydrophilic packing in a catalytic exchange column. The exchange column has been studied in detail for various operating conditions in this study. The intrinsic kinetics for the catalytic reaction was determined through spinning basket reactor experiments, and activation energy was estimated to be 29.7 kJ/mol. The overall mass transfer co-efficient in a mixture of hydrophilic packing and hydrophobic catalyst packed bed was determined experimentally in a pilot scale counter current trickle bed reactor to be in the range of 0.15–0.25 s-1 for the proposed range of operating conditions. Individual mass transfer resistances for vapour-liquid mass transfer, external gas mass transfer and gas-solid mass transfer were estimated using widely accepted empirical correlations. Under benchmark operating conditions, the Damkohler number for the exchange column was found to be between 0.10 and 0.16, indicating a significant contribution of surface reaction to overall mass transfer resistance. The vapour liquid mass transfer was found to be fast compared to the gas-vapour reaction. Therefore, increasing hydrophobic catalyst proportion relative to hydrophilic packing was found to increase the overall mass transfer. A steady state process model has been developed to predict the performance of overall exchange process using the experimentally determined parameters. Validation of the process model was carried out using the experimental data generated on the pilot scale trickle bed reactor. Optimum operating conditions of temperature, hydrophobic catalyst to hydrophilic packing ratio, gas and liquid superficial velocities were determined.

Tritium Extraction from Water

Tritiated wate`r production is ubiquitous in facilities that handle tritium gas. Sources range from decontamination efforts, to the deliberate conversion of elemental tritium to tritiated water in processes that strive to reduce emissions to the environment, to gaseous effluents to the environment. At low concentrations, ranging from a few μCi/L to mCi/L, high throughputs are required to process the high-volume, low-activity water. Combined electrolysis and catalytic exchange (CECE) shows promise by offering high throughput, reliability, economic viability, and facile coupling to isotopic separation systems if necessary. This paper will discuss the features of two production-scale CECE facilities: a 7 m3/h throughput system that uses an alkaline electrolysis cell and a 21 m3/h throughput system that uses a proton exchange membrane electrolysis cell. The former is in service and has been modified to improve reliability; the latter is in the initial stages of commissioning.

Water Detritiation System for ITER—Evaluation of Design Parameters

The Water Detritiation System (WDS) designed for ITER is based on the combined electrolysis and catalytic exchange(CECE) process to ensure the emission of tritium to the environment is maintained below very strict limits. The CECE process is one of the processes for tritium removal that CNL (Canadian Nuclear Laboratories, formerly Atomic Energy of Canada Ltd.) has studied, developed and successfully demonstrated. In this work, CNL evaluated ITER’s design conditions of the exchange column and the electrolyser – the two key components of the CECE process (and the ITER WDS system) – to assess the effectiveness of tritium removal and investigate options to improve it. The evaluation was done using CNL’s CECE process simulation according to a protocol set out by ITER. Initially, calibration (benchmarking) of CNL’s hydrogen-water exchange column model was performed with a standard data set for a specified column to determine modeling parameters that resulted in a good match with the tritium concentration data. The model was then applied (with the same parameters) to the current WDS design. Some optimized conditions for the CECE process that could improve performance of the WDS to meet its design criteria were determined. The details of some of these assessments are presented here with particular attention to the WDS case where the feed water contains high levels of deuterium.

Mass Transfer Model Liquid Phase Catalytic Exchange Column Simulation Applicable to any Column Composition Profile

Liquid Phase Catalytic Exchange (LPCE) is a key technology used in water detritiation systems. Rigorous simulation of LPCE is complicated when a column may have both hydrogen and deuterium present in significant concentrations in different sections of the column. This paper presents a general mass transfer model for a homogenous packed bed LPCE column as a set of differential equations describing composition change, and equilibrium equations to define the mass transfer driving force within the column. The model is used to analyze Combined Electrolysis and Catalytic Exchange (CECE) sensitivity to deuterium accumulation in the electrolyser.

Setup and commissioning of a combined water detritiation and isotope separation experiment at the Tritium Laboratory Karlsruhe

The European union in kind supply for the ITER fuel cycle development consists, among others, of the water detritiation system (WDS) and the isotope separation system (ISS). In order to mitigate the release of tritium to the environment, these systems are combined by feeding hydrogen exhaust from the ISS into the WDS for final processing. Therefore, the WDS is the final tritium barrier before releasing hydrogen (H2) exhaust to the environment.The TRENTA 4 scaled prototype facility at TLK is based on combination of the combined electrolysis and catalytic exchange (CECE) process and a cryogenic distillation (CD) process. All components are fully tritium compatible and controlled using a state of the art control system for process automation, backed up by an additional dedicated safety system.The paper will give a detailed overview of the current experimental facility including all process components. Furthermore the paper will present the results of the functional test of the WDS/ISS combination using protium and deuterium, as well the results of the first commissioning runs using HTO of approximately 5×109Bqkg−1 activity concentration.

A Small Closed-Cycle Combined Electrolysis and Catalytic Exchange Test System for Water Detritiation

AECL has been actively involved in exploring advanced electrolysis technologies for its Combined Electrolysis and Catalytic Exchange (CECE) technology for water detritiation. A small-scale CECE system (mini-CECE) has been built and operated at AECL to explore its operation as a closed-cycle system with a proton-exchange membrane (PEM) type electrolysis cell. A similar mini-CECE system suitable for service with tritium concentrations up to 1000 Ci/kg(water) has been assembled, in collaboration with Tyne Engineering, for installation in a glovebox in AECL’s Tritium Facility. These systems were developed as test-beds for membranes that had been selected for their expected tritium resistance. The systems allowed the measurement of membrane performance over long periods at very high tritium concentrations, as well as the ability to monitor any effects of membrane degradation products on the performance of exchange and recombiner catalysts.Preliminary work has been done with Nafion-112 membrane samples by exposing them to gamma and beta radiation to determine their suitability for use in tritiated CECE system. Doses of up to 1250 kGy of gamma or 200 kGy of beta were applied. Visual observations showed that gamma irradiation at doses below 400 kGy produced severe damage to the membrane. No significant physical damage was observed for samples exposed to 200 kGy from tritiated water. However this level of exposure to either gamma or beta radiation was sufficient to significantly decrease membrane performance in fuel cell tests.

Performance Characterization of Hydrogen Isotope Exchange and Recombination Catalysts for Tritium Processing

AECL’s hydrogen isotope exchange catalyst and recombination catalysts have been successfully applied to a wide range of industrial tritium-removal applications. The catalysts are used for Liquid Phase Catalytic Exchange (LPCE) and for gas-phase and trickle-bed recombination of hydrogen isotopes and have led to process simplification, improved safety and operational advantages.Catalyst performance design equations derived from laboratory testing of these catalysts have been validated against performance under industrial conditions. In a Combined Electrolysis and Catalytic Exchange (CECE) demonstration plant analyses of LPCE and recombiner efficiency were carried out as a function of catalyst activity over a wide range of operation. A steady-state process simulation used to model and design the hydrogen-water isotopic exchange processes, such as the CECE detritiation plant, was validated using the results of this demonstration.Catalyst development for isotope-exchange and recombination applications has continued over the last decade. As a result, significant improvements in catalyst performance have been achieved for these applications. This paper outlines the uniqueness of AECL’s specialized catalysts and process designs for these applications with examples from laboratory and industrial case studies.

Fifteen Years of Operation of CECE Experimental Industrial Plant in PNPI

The experimental industrial plant for hydrogen isotope separation on the basis of the Combined Electrolysis and Catalytic Exchange (CECE) process has been operating safely and reliably for 15 years in Petersburg Nuclear Physics Institute (PNPI). The plant has been designed to carry out the development of CECE process. In parallel with study of hydrogen isotope separation by CECE process the facility is used for processing heavy water wastes contaminated by tritium. The plant produces reactor quality heavy water and heavy water with reduced content of tritium less than 105 Bq/kg. The plant has been modified several times since its put into operation in 1995. This paper summarizes the CECE technology development and experience gained during the upgrade of facility, replacement of failed components and operation of the plant since its commissioning in 1995.

Simulation of CECE Facility for Water Detritiation

This paper presents a program to simulate performance of a liquid phase catalytic exchange (LPCE) column of a water detritiation facility based on combined electrolysis and catalytic exchange (CECE) technology over a wide range of deuterium contents in a feed stream. The program uses rate constants of the chemical isotopic exchange reactions between gaseous hydrogen and water vapor occurring on a hydrophobic catalyst and the mass transfer rate between water vapor and the film of liquid water on packing material in the LPCE column, which have been measured experimentally using a specially developed method and at a low concentration of deuterium in a three-isotope mixture. The effect of the deuterium presence on the kinetics of isotopic exchange reactions and the performance of the LPCE column are taken into account considering several possible mechanisms that can control the overall rate of reaction. Selection of the most suitable mechanism was carried out by comparing the simulations with the results of an experimental test with a large deuterium content.The simulation program allows calculation of isotope profiles in streams of liquid water, water vapor, and gaseous hydrogen along the LPCE column over a very wide range of isotopic compositions and for CECE facilities of several different layouts.

Heavy water purification from tritium by CECE process

The experimental industrial plant for hydrogen isotope separation on the basis of the Combined Electrolysis and Catalytic Exchange (CECE) process is operated trouble free over a period of more than 10 years in Petersburg Nuclear Physics Institute. In parallel with carrying out the research of CECE process the plant is used for reprocessing heavy water wastes contaminated by tritium; several tons of reactor quality heavy water have been conditioned. The plant was updated to provide high factor of heavy water detritiation. Detritiation factor of about 2000 was achieved and heavy water with reduced contents of tritium less than 10 5 Bq/kg was withdrawn at the rate of 7–9 kg/day as a top product. The experience gained during the plant operation shows the high efficiency of hydrogen isotope separation with CECE process. This process can be used for tritium and protium removal from reactor heavy water.

The performance of a trickle-bed reactor packed with a Pt/SDBC catalyst mixture for the CECE process

The combined electrolysis and catalytic exchange (CECE) process with a hydrophobic catalyst is a very effective method to remove small quantities of tritium from light or heavy wastewater streams because of its high separation factor and mild operating conditions. A hydrophobic platinum/styrene-divinyl benzene copolymer (Pt/SDBC) catalyst which was developed for the liquid-phase catalytic exchange (LPCE) column of the Wolsong tritium removal facility (WTRF) has been tested in a trickle bed reactor for the design of the CECE process. An experimental apparatus has been built for the testing of the catalyst at various temperatures and gas velocities. The catalyst column was packed with a mixture of a hydrophobic catalyst and a hydrophilic packing (Dixon gauze ring) to improve the liquid distribution and vapor/liquid transfer area. Many tests have been carried out at Korea Atomic Energy Research Institute (KAERI) to measure the activity of the catalyst, K y a (1 s −1), under various operating conditions. K y a increases with the hydrogen flow rates in the range of 0.4–1.6 m s −1 at STP. The height of the catalyst column was determined from these K y a values according to the reaction temperatures and hydrogen flow rates.

Development of a Heavy Water Detritiation Plant for PIK Reactor

The research reactor PIK should be supplied with a Detritiation Plant (DP) to remove tritium from heavy water in order to reduce operator radiation dose and tritium emissions. The original design of the reactor PIK Detritiation Plant was completed several years ago. A number of investigations have been made to obtain data for the DP design. Nowadays the design of the DP is being revised on a basis of our investigations. The Combined Electrolysis and Catalytic Exchange (CECE) process will be used at the Detritiation Plant instead of Vapor Phase Catalytic Exchange. The experimental industrial plant for hydrogen isotope separation on the basis of the CECE process is under operation in Petersburg Nuclear Physics Institute. The plant was updated to provide a means for heavy water detritiation. Very high detritiation factors have been achieved in the plant. The use of the CECE process will allow the development of a more compact and less expensive detritiation plant for heavy water reactor PIK.

Development and Improvement of Devices for Hydrogen Generation and Oxidation in Water Detritiation Facility Based on CECE Technology

Water detritiation facility based on CECE (Combined Electrolysis and Catalytic Exchange) technology needs an electrolyser for water conversion to hydrogen. Use of a conventional alkali electrolyser requires a very deep purification of hydrogen stream from alkali prior to injection to LPCE (Liquid Phase Catalytic Exchange) column. In some applications conversion of detritiated hydrogen back into water is required. This is usually performed via hydrogen catalytic oxidation in a recombiner. This paper presents results of study to improve hydrogen and oxygen purification for alkali electrolysers and develop a hydrogen recombiner based on use of hydrophobic catalyst.

Modeling of the Process of Three-Isotope (H, D, T) Exchange between Hydrogen Gas and Water Vapour on Pt-SDBC Catalyst over a Wide Range of Deuterium Concentration

The large scale studies of Combined Electrolysis and Catalytic Exchange (CECE) process in Petersburg Nuclear Physics Institute showed a complicated influence of various factors on the process caused by the presence of two simultaneous isotope exchange sub processes: counter-current phase exchange (between liquid water and water vapour) and co-current catalytic exchange (between hydrogen gas and water vapour). A laboratory scale set-up of glass made apparatuses was established in such a way that it allows us to study phase and catalytic exchange apart. A computer model of the set-up has been developed.The catalytic isotope exchange model formulation is presented. A collection of reversible chemical reactions is accompanied by diffusion of the gaseous reactants and reaction products in the pores of catalyst carrier. This has some interesting features that are demonstrated. Thus it was noted that the flow rates ratio (gas to vapour - λ = G/V) as well as the concentrations of reactants exert influence on the process efficiency.

Heavy water detritiation by combined electrolysis catalytic exchange at the experimental industrial plant

The experimental industrial plant has been in operation in Petersburg Nuclear Physics Institute to develop the combined electrolysis and catalytic exchange (CECE) process for hydrogen isotope separation since 1995. The plant is also used for processing tritiated heavy water waste; several tons of reactor quality heavy water have been obtained. Last year, the plant was updated to provide a means for heavy water detritiation with high detritiation factor. This paper describes the experimental results for heavy water detritiation. During heavy water purification from tritium detritiation factor about 10 3 was achieved. Heavy water with reduced contents of tritium less than 10 5 Bq/kg was withdrawn at the rate of 4.5 kg per day as a top product. The sample points located along the separation column allowed obtaining tritium concentration profiles within the column. The experimental data are compared with the ones predicted by computer simulation. CECE process is attractive for use in the heavy water hi-flux PIK reactor detritiation plant. This process can find an application at the ITER (International Thermonuclear Experimental Reactor) fusion facility.

Demonstration of Very High Detritiation Factors with a Pilot-Scale CECE Facility

ABSTRACTAnalysis of process data from initial detritiation tests in a pilot-scale Combined Electrolysis and Catalytic Exchange (CECE) Facility1 indicated that very high detritiation factors (DFs), at least 10 000, could be achieved in the facility. Performance requirements for process equipment were evaluated and some minor refinements were made to selected components. In particular, the recombination efficiency of tritium in the electrolytic oxygen stream was improved and the tritiated-water feed point was moved to a location lower in the catalyst column. With these modifications, the facility was able to remove more than 99.998% of the tritium (i.e., achieve a DF greater than 50 000) from a heavy water feed stream containing 330 GBq/kg, with 7.8 TBq/kg in the electrolysis cell. The processing rate at these conditions was about 2.2 Mg/a, compared with a rate of 5 Mg/a for a DF of 180.