Combined Electrolysis Catalytic Exchange Process Research Articles

Integration of a Microchannel Reactor in a CECE Process for H2 Removal from the O2 Stream Produced by the H2 Generator

A hydrogen generator is used in the combined electrolysis catalytic exchange process (CECE) for low-level tritiated water detritiation as a source of H2 (Q2) for the liquid-phase catalytic exchange column(s) within the process. To produce H2, the H2 generator employs an electrolytic process for H2O splitting into H2 and O2, resulting two streams: a hydrogen stream and an oxygen stream. During the detritiation of water, tritium is accumulated in the H2 generator in the form of tritiated water, and the effluent streams (hydrogen and oxygen) show in time an increased tritium concentration in the form of both tritiated water vapors and gas, which need to be recovered. The traditional methods for recovery present a risk of explosion due to the high concentration of hydrogen in oxygen (above 3%, while the explosion limit is 1%). In order to minimize this risk, a microchannel reactor with platinated channels has been developed and tested for the oxidation of tritiated hydrogen from the O2 electrolyzer stream in view of its recovery in a scrubber column and returned as tritiated water to the process. The reactor has been coupled to an electrolyzer and tested with regard to the operating temperature. It has been found that it reaches the highest oxidation efficiency of hydrogen when operated at 200°C. The design of the equipment is presented together with the results of the tests done with the equipment integrated in the CECE process.

Experimental Investigation of CECE Process to Recover Tritium and Deuterium from Low Tritiated/Deuterated Liquid Waste

A current concern of researchers from the Experimental Pilot Plant for Tritium and Deuterium Separation (PESTD) within the National R&D Institute for Cryogenics and Isotopic Technologies in Rm. Valcea is the solution of a combined electrolysis catalytic exchange (CECE) isotopic separation process that aims to be part of a new liquid waste decontamination technology. The experimental installation, defined as module M1100, has interfaces with the PESTD process and auxiliary systems and is placed within the PESTD area. The installation has its own automation and control system that allows for safe operation. Two operating modes are presented. The first mode is in “open-circuit” mode to evaluate the individual separation performances of the two technological processes, water electrolysis and water-hydrogen catalytic isotopic exchange, respectively. The second mode is in “closed loop,” which corresponds to the CECE isotopic separation process where the tritium/deuterium are concentrated in the water within the electrolyzer. The preliminary experimental investigations were performed with low-concentrated tritiated water (HTO; ~100 Bq/l] in order to have a reduced degree of contamination as the concentration of the processed water was increased (~1000 Bq/l). The evaluation of the separation performances was made by comparing correlations from direct measurements with the calculated ones provided by the software developed for the CECE isotopic separation process in the open-circuit operating mode. For the closed-loop operation mode, the data provided by the calculation program for the representation of the nonstationary CECE isotopic separation regime were compared with the measured data. The preliminary results show a good correlation between the measured and the calculated data considering these experiments were carried out mainly in order to improve the operating performance.

MICRO-CHANNEL REACTOR FOR LOW LEVEL H2 OXIDATION WITHIN AN O2 STREAM: PRELIMINARY TESTS IN VIEW OF INTEGRATION IN A H2 GENERATOR WITHIN CECE PROCESS

CECE (Combined Electrolysis Catalytic Exchange) process is the candidate for low level tritiated water detritiation within any application. The process consists mainly of a H2 generator, a LPCE (Liquid Phase Catalytic Exchange) column and an O2 striping column. During operation, tritium is being accumulated within the H2 generator in the form of tritiated water and the effluent streams (hydrogen and oxygen) show in time an increase concentration in tritium in the form of both tritiated water vapors and gas, which needs to be recovered. The tritium in the H2 stream is recovered in a LPCE column, while the tritium in the O2 stream is recovered in a striping column. In view of lowering the load onto the striping column and to recover the tritium in gas form, a micro-channel reactor is proposed to be included for H2 oxidation followed by vapor recovery. The design of the equipment together with the preliminary results of the tests done with H2 and air will be shown, prior to integration in the CECE process.

The Current Status of the Heavy Water Detritiation Facility at the NRC (Kurchatov Institute) – PNPI

The multifunctional Tritium Removal Facility (TRF) has been designed for the heavy water research reactor PIK in Russia. Along with the extraction of tritium and protium from a heavy water reflector of the reactor, the TRF provides the processing of heavy water waste and the production of tritium-free heavy water. The combined electrolysis catalytic exchange process and hydrogen cryogenic distillation are used at the TRF. A number of investigations have been made to obtain data for the TRF design. At present, the facility is under construction and a detailed design is being completed. The possibility of processing heavy water waste to produce heavy water simultaneously with the extraction of tritium and protium from the heavy water reactor will improve the functionality and economic efficiency of the TRF. The basic technological scheme of the facility and the main modes of its operation are presented along with the progress of the construction of the facility building and engineering systems.

The Study of CECE Process for Low-Tritiated Liquid Waste Prior to Experimental Phase

In order to ensure the efficient management of radioactive waste in the form of tritiated light water and tritiated heavy water with low tritium and/or deuterium concentration, Institute for Cryogenics and Isotopic Technologies (ICSI) Rm.Valcea is developing an experimental demonstration facility based on the combined electrolysis catalytic exchange (CECE) separation process. The facility is completing the experimental pilot plant for tritium and deuterium separation—the installation support for heavy water detritiation from the CANDU reactors in Romania. The concentration of deuterium from low-concentrated waste extends the recovery area from below 1% D2O/(D2O + H2O), corresponding to the minimum threshold of the Cernavoda Upgrading Facility, thus contributing to the reduction of heavy water losses. At the same time the tritium recovery process will be increased. The experimental installation has an innovative solution that reconfigures a proton exchange membrane (PEM) electrolyzer for tritium qualification thereby improving equipment specific to hydrogen isotope separation processes. This paper presents the experimental installation conceptual scheme, including the measurement and control elements. A modeling software for simulation of the nonsteady-state regime of the CECE separation process, specific to the deuterium/tritium isotopes concentration process in the liquid phase, is also presented. The mathematical model integrates the characteristic equations of separation by liquid phase catalytic exchange (LPCE), the mathematical representation of isotope separation by electrolysis, and the water distillation from the oxygen purification process in a nonstationary regime. An analysis is presented for the concentration of various low-concentrated tritium waste. We also investigate the influence of the electrolyzer liquid holdup and the isotopic separation column holdup on concentrated water production.

Enhanced configuration of a water detritiation system; impact on ITER Isotope Separation System based cryogenic distillation

Tritiated water is generated in the ITER systems by various sources and may contain deuterium and tritium at various concentrations. The reference process for the ITER Water Detritiation System is based on Combined Electrolysis Catalytic Exchange (CECE) configuration. During long time operation of the CECE process, the accumulation of deuterium in the electrolysis unit and consequently along the Liquid Phase Catalytic Exchange (LPCE) column is unavoidable with consequences on the overall detritiation factor of the system. Beside the deuterium issue in the process, the large amount of the tritiated water with tritium activity up to 500Ci/kg in the electrolysis cells is a concern from the safety aspect of the plant.The enhanced configuration of a system for processing tritiated water allows mitigation of the effects due to deuterium accumulation and also reduction of tritium inventory within the electrolysis system. In addition the benefits concerning to the interface between the water detritiation system and tritium recovery based cryogenic distillation are also presented.

Operational Characterization of a Combined Electrolysis Catalytic Exchange Process

Many current CECE systems, which are used to extract harmful tritium from heavy water nuclear reactors, operate with inefficient alkaline electrolyzers that contain dangerous caustic chemicals. Thus the Hydrogen Isotope Branch at Chalk River Laboratories developed and integrated a safer and more efficient PEM electrolyzer to replace the alkaline electrolyzer. In this research, a bench-scale CECE system with a PEM type electrolyzer at Chalk River Laboratories was tested at LPCE column temperatures of 20°C, 40°C and 60°C to determine baseline operational parameters and conditions for optimal isotopic exchange. Increased operational temperature led to greater isotopic exchange across the PEM electrolyzer but not the LPCE column, an irregularity likely caused by an insufficient amount of catalyst in the column. Increased LPCE temperature also led to a decrease in overall system flow stability. Finally, the PEM electrolyzer voltage exhibited an unusual sharp rise throughout testing, indicating the membrane's susceptibility to damage if used without proper conditioning. Research conclusions will be taken into consideration in setting up a new bench-scale CECE process that more accurately models tritium extraction using a PEM electrolyzer.

Water detritiation processing of JET purified waste water using the TRENTA facility at Tritium Laboratory Karlsruhe

A Water Detritiation System (WDS) is required for any Fusion machine in order to process tritiated waste water, which is accumulated in various subsystems during operation and maintenance. Regarding the European procurement packages for the ITER tritium fuel cycle, the WDS test facility TRENTA applying the Combined Electrolysis Catalytic Exchange (CECE) process was developed, installed and is currently in operation at the Tritium Laboratory Karlsruhe (TLK).Besides the on-going R&D work for the design of ITER WDS, the current status of the TRENTA facility provides the option to utilize the WDS for processing tritiated water. Therefore, in the framework of the EFDA JET Fusion Technology Work Programme 2011, the TLK was able to offer the capability on a representative scale to process tritiated water, which was produced during normal operation at JET. The task should demonstrate the availability of the CECE process to handle and detritiate the water in terms of tritium enrichment and volume reduction.The operational program comprised the processing of purified tritiated water from JET, with a total volume of 180l and an activity of 74GBq. The paper will give an introduction to the TRENTA WDS facility and an overview of the operational procedure regarding tritiated water reduction. Data concerning required operation time, decontamination and enrichment performances and different operating procedures will be presented as well. Finally, a preliminary study on a technical implementation of processing the entire stock of JET tritiated water by means of water reduction and tritium recovery and an impact of storage capacity at JET will be discussed.

Modification of a solid polymer electrolyte (SPE) electrolyser to ensure tritium compatibility

A Water Detritiation System (WDS) is required for the ITER Tritium Plant in order to process tritiated water which is accumulated in various subsystems (e.g. the hall ventilation systems). For the ITER-WDS, the Combined Electrolysis Catalytic Exchange (CECE) process with an electrolyser unit as one of the major components is envisaged. An experimental WDS was built and commissioned at the Tritium Laboratory Karlsruhe (TLK) for the investigation of various subsystems of the CECE process in tritium environment. The TLK-WDS consists of an 8 m Liquid Phase Catalytic Exchange column and two Solid Polymer Electrolyte electrolysers, each with a maximum hydrogen output of 1 m 3/h. The commercially available Hogen40 electrolyser units from Proton Energy Systems are not tritium compatible concerning materials, joints and quality documentation (e.g. necessary certificates). In order to process tritiated water with tritium concentrations up to 370 GBq/kg, tritium compatibility had to be ensured by appropriate modifications. Up to now, the modified system has been operated with tritiated water for 3500 h, the maximum tritium concentration in the electrolysers being 190 GBq/kg. This contribution reports on the necessary modifications of the electrolyser units and the experiences gained thereby. The results are equally important for the ITER-WDS, where the maximum tritium concentration in the feed water of the electrolyser units will be even higher with 11 TBq/kg.

Effects of the gas–liquid ratio on the optimum catalyst quantity for the CECE process with a homogeneously packed LPCE column

In order to improve the separative performance of a combined electrolysis catalytic exchange (CECE) process, we have carried out experimental studies on hydrogen isotope separation by a CECE process using a liquid phase catalytic exchange (LPCE) column of trickle-type packed beds. Two types of trickle beds were tested in our previous study. One was the layered bed, where layers of Kogel catalysts and Dixon gauze rings were alternately filled in the column. The other was the homogeneous bed, where Kogel catalysts and Dixon gauze rings were homogeneously mixed and filled in the column. We found that (1) the homogeneously packed bed was more efficient than the layered packed bed, and (2) the catalyst quantity was optimal, which resulted in the highest separative performance. In this study, the effect of the gas–liquid ratio ( G/ L) on the optimum catalyst quantity was studied experimentally in a homogeneously packed bed. When the value of G/ L was 1.7, total separation factors were relatively small and the optimum catalyst quantity could not be determined. On the other hand, when the values of G/ L were 0.9 and 0.7, the values of the total separation factors had maximums and the optimal quantities of the catalyst were clearly obtained.

Present status of hydrogen isotope separation by CECE process at the NIFS

At the National Institute for Fusion Science experimental studies on hydrogen isotope separation by a combined electrolysis catalytic exchange (CECE) process have been carried out in order to apply it to the system of water detritiation for D–D burning experiments of the large helical device (LHD). Isotope separation experiments of hydrogen and deuterium are performed with two types of packed beds filled with Kogel catalysts (4.0–6.7 mm spherical, 0.8 wt% Pt deposited) and Dixon gauze rings (6 mm outer diameter, 6 mm height). One is the layered bed where layers of Kogel catalysts and that of Dixon gauze rings are filled in the column alternately. The other is the homogeneous bed where Kogel catalysts and Dixon gauze rings are mixed and filled in the column homogeneously. The separative performance of the homogeneous bed is appreciably greater than that of the layered bed, where the quantities of the catalysts are equal for both beds. The homogeneous packed bed exhibits fine performances; pressure drop is small in the range of 40–300 Pa/m and the coefficient of vapor-liquid mass transfer becomes more than 900 kmol/m 3/h, while the superficial velocity is in the range 0.2–0.7 m/s.

Hydrogen Isotope Separation by Combined Electrolysis Catalytic Exchange Under Reduced Pressure

At the National Institute for Fusion Science experimental studies on hydrogen isotope separation by a Combined Electrolysis Catalytic Exchange (CECE) process have been carried out in order to apply it to the system of water detritiation for D-D burning experiments of the Large Helical Device. As an improvement of the CECE process, we have developed a reduced-pressure method as a means of enhancing the separation factor. The feasibility of this method is examined through application to a CECE process using a prototype separation column. Hydrogen-deuterium isotope separation experiments are performed in the two cases where column pressures are 12 and 101 kPa, and the separation factors for hydrogen and deuterium are obtained as 6.8 and 5.6, respectively. It is confirmed that the present method is applicable and useful to the CECE process. The values of Height Equivalent to a Theoretical Plate (HETP) are estimated by analyses with the equilibrium stage model. The HETP values are 15 cm at 12 kPa and 13 cm at 101 kPa. The increase of superficial velocity with decreasing pressure may spoil the efficiency of the mass transfer.

Design and Operational Experience with a Pilot-Scale CECE Detritiation Process

ABSTRACTA 5 Mg/annum Combined Electrolysis Catalytic Exchange (CECE) Facility was designed, constructed and operated to demonstrate the CECE process for heavy water detritiation. In this demonstration facility, a liquid-phase catalytic exchange (LPCE) column, using AECL’s wetproofed catalyst, separated tritium from deuterium and a specially designed, low-inventory electrolytic cell provided tritium-enriched deuterium to the LPCE column. An overhead recombiner, also using wetproofed catalyst, produced detritiated heavy water. Tritium was removed from the electrolysis cell as tritiated deuterium gas and packaged as a titanium deuteride. The design detritiation factor of 100 was readily achieved using a 370 GBq/kg heavy water feed. Design features, operational experience and results from the 4-month, 2 000-h operation are described.

CANDU with hydrogen

How Canada's successful CANDU ( CANada Deuterium Uranium) nuclear power reactors would benefit from an emerging hydrogen-electric economy and vice versa is discussed with reference to the Combined Electrolysis Catalytic Exchange (CECE) process for recovering byproduct heavy water from electrolytic hydrogen. At the heart of this process is a hydrophobic, dispersed-platinum catalyst which has been under development at Chalk River for about a decade. Other potential applications of the CECE process are presented, including tritium recovery from both light and heavy water. Based on preliminary data and cost estimates, the net heavy water dollar credit appears to be at least comparable to the byproduct oxygen credit of electrolytic hydrogen. The potential for byproduct heavy water production from hydrogen in general, and from electrolytic hydrogen in particular, is discussed in relation to Canada's present primary heavy water production capacity.