R. Michling

Behavior of solid polymer membrane electrolyzers in use with highly tritiated water

Abstract These days more and more modern electrolysis cells are operated with new solid polymer membranes. These membranes prevailing DuPont’s Nafion® are not only used for electrolysis but as well for the wide spectrum of fuel cells due to their good mechanical and chemical stability and the high proton conductivity. For that reason it is intended to use these solid polymer membranes for the electrolyzer units in the ITER Water Detritiation System (WDS). The influence of Tritium during water electrolysis to the membrane material is still not sufficiently investigated. Therefore long-term experiments of solid polymer membranes were performed at Tritium Laboratory Karlsruhe (TLK). The chemical degradation and durability behavior of the used Nafion® 117 membrane are investigated in details under tritiated water conditions. For comparison a second cell was operated with demineralized water for the same period. In addition to the experimental rigs with single Nafion® membranes, two industrial electrolyzer units equipped with Nafion® membranes were operated during different tritium experiments at TLK. Before operation they had been modified to be compatible for tritium operation. After long operation period no degradation in the performance of the electrolyzers is observable.

Experiments on water detritiation and cryogenic distillation at TLK. Impact on ITER fuel cycle subsystems interfaces

Abstract The ITER Isotope Separation System (ISS) and Water Detritiation System (WDS) should be integrated in order to reduce potential chronic tritium emissions from the ISS. This is achieved by routing the top (protium) product from the ISS to a feed point near the bottom end of the WDS Liquid Phase Catalytic Exchange (LPCE) column. This provides an additional barrier against ISS emissions and should mitigate the memory effects due to process parameter fluctuations in the ISS. To support the research activities needed to characterize the performances of various components for WDS and ISS processes under various working conditions and configurations as needed for ITER design, an experimental facility called TRENTA representative of the ITER WDS and ISS protium separation column, has been commissioned and is in operation at TLK. The experimental program on TRENTA facility is conducted to provide the necessary design data related to the relevant ITER operating modes. The operation availability and performances of ISS-WDS have impact on ITER fuel cycle subsystems with consequences on the design integration. The preliminary experimental data on TRENTA facility are presented.

Infrared Spectroscopy in Liquid Hydrogen Isotopologues for the ISS of ITER

Abstract The ITER project aims at demonstrating the technical feasibility of nuclear fusion in a DT plasma. One of the important steps towards a functional fusion power plant is the development of a stable and reliable fuel cycle. Major developments on this field are made at the Tritium Laboratory Karlsruhe (TLK). In this paper the design and installation of an analysis apparatus for tritium concentrations via InfraRed (IR) absorption for engagement in the ITER ISS is described. The IR analysis is performed in the liquid hydrogen phase at the bottom of a cryogenic distillation column similar to those foreseen for ITER ISS. Technical constraints and physical boundary conditions are presented as well as experimental methods and preliminary results. The technical feasibility is shown and suggestions for further development of IR spectroscopy for ITER appliances are given.

Performance Tests of Tritium Separation by LPCE Column at TLK Facility

Abstract The research for the performance improvement of the Liquid Phase Chemical Exchange (LPCE) column has been carried out at Nagoya University in collaboration with National Institute for Fusion Science (NIFS) and Tritium Laboratory Karlsruhe (TLK). Kogel catalysts and Dixon gauze rings were mixed at a certain ratio and packed in the column in a random manner. Performance tests of tritium separation by the column using tritiated water of 26 kBq/cm3 in the electrolyzer were performed at the TLK experimental facility. An effect of axial mixing on the separative performance of the column was examined by a stage-wise model, named “Channeling stage model.” It was suggested by the analyses that quite a long-distance axial mixing generated in the water phase.

Highly tritiated water processing by isotopic exchange

Abstract Three kinds of Pt-catalyzed zeolite were tested as candidates for isotopic exchange of highly tritiated water (HTW), and CBV 100 CY (Na-Y, Si/Al~5.0) shows the best performance. Small-scale tritium testing indicates that this method is efficient for reaching an exchange factor (EF) of 100. Full-scale non-tritium testing implies that an EF of 300 can be achieved in 24 hours of operation if a temperature gradient is applied along the column. For the isotopic exchange, deuterium recycled from the Isotope Separation System (deuterium with 1% T and/or 200 ppm T) should be employed, and the tritiated water regenerated from the Pt-catalyzed zeolite bed after isotopic exchange should be transferred to Water Detritiation System (WDS) for further processing.

Micro-Channel Catalytic Reactor Integration in Caper and R&D on Highly Tritiated Water Handling and Processing

Abstract The CAPER facility of the Tritium Laboratory Karlsruhe has demonstrated the technology for the tokamak exhaust processing. CAPER has been significantly upgraded to pursue R&D towards highly tritiated water (HTW) handling and processing. The preliminary tests using a metal oxide reactor producing HTW afterward detritiated with PERMCAT were successful. In a later stage, a micro-channel catalytic reactor was installed in view of long term R&D program on HTW. The integration of this new system in CAPER was carried out along with a careful safety analysis due to high risk associated with such experiments. First experiments using the μ-CCR were performed trouble free, and HTW up to 360 kCi/kg was produced at a rate of 0.5 g/h. Such HTW was collected into a platinized zeolite bed (2 g of HTW for 20 g of Pt-zeolite), and in-situ detritiation was performed via isotopic exchange with deuterium. These first experimental results with tritium confirmed the potential for the capture and exchange method to be used for HTW in ITER.

Capture and isotopic exchange method for water and hydrogen isotopes on zeolite catalysts up to technical scale for pre-study of processing highly tritiated water

Abstract Highly tritiated water (HTW) may be generated at ITER by various processes and, due to the excessive radio toxicity, the self-radiolysis and the exceedingly corrosive property of HTW, a potential hazard is associated with its storage and process. Therefore, the capture and exchange method for HTW utilizing Molecular Sieve Beds (MSB) was investigated in view of adsorption capacity, isotopic exchange performance and process parameters. For the MSB, different types of zeolite were selected. All zeolite materials were additionally platinized. The following work comprised the selection of the most efficient zeolite candidate based on detailed parametric studies during the H2/D2O laboratory scale exchange experiments (~25 g zeolite per bed) at the Tritium Laboratory Karlsruhe (TLK). For the zeolite, characterization analytical techniques such as Infrared Spectroscopy, Thermogravimetry and online mass spectrometry were implemented. Followed by further investigation of the selected zeolite catalyst under full technical operation, a MSB (~22 kg zeolite) was processed with hydrogen flow rates up to 60 mol h-1 and deuterated water loads up to 1.6 kg in view of later ITER processing of arising HTW.

High level tritiated water monitoring by bremsstrahlung counting using a silicon drift detector

Abstract The β-ray induced X-ray spectrometry (BIXS) is a promising technique to monitor the tritium concentration in a fuel cycle of a fusion reactor. For in-situ measurements of high level tritiated water by bremsstrahlung counting, the characteristics of a low-noise silicon drift detector (SDD) have been examined at the Tritium Laboratory Karlsruhe (TLK). In static measurements with constant sample volume and tritium concentration, the bremsstrahlung spectra of tritiated water samples in a concentration range of 0.02 to 15 MBq/ml have been observed. The volume has been kept constant at 5 cm3. The observed spectra are well above the noise threshold. In addition to X-rays induced by β-rays, the spectra feature X-ray fluorescence peaks of the surrounding materials. No indications of memory effects have been observed. A linear relation between the X-ray intensity and the tritium concentration was obtained and the lower detection limit of the setup has been determined to 1 MBq ml-1, assessed by the Currie criterion. In addition, the spectra obtained experimentally could be reproduced with high agreement by Monte-Carlo simulations using the Geant4-toolkit. It was found that the present detection system is applicable to non-invasive measurements of high-level tritiated water and the SDD is a convenient tool to detect the low energy bremsstrahlung X-rays.