T. L. Le

Tritium tests with a technical PERMCAT for final clean-up of ITER exhaust gases

One of the design targets for the ITER Tokamak Exhaust Processing system is not to lose more than 10−5 g h−1 into the Normal Vent Detritiation System of the Tritium Plant. The plasma exhaust gas, therefore, needs to be processed in a way that an overall tritium removal efficiency of about 108 is reached. Such a high decontamination factor can only be achieved by multistage processes. The third step of the three step CAPER process developed at the TLK is based on a so-called permeator catalyst (PERMCAT) reactor, a direct combination of a Pd/Ag permeation membrane and a catalyst bed. The PERMCAT principle is based on isotopic swamping in a counter current mode. Previous tritium experiments employing laboratory scale PERMCAT reactors have revealed decontamination factors as high as 105 for the third CAPER step. First tritium tests with a technical scale PERMCAT reactor led to similar decontamination factors and clearly demonstrated that the required overall ITER decontamination factor can be reached with a technical PERMCAT as the final clean-up step of the CAPER process.

Successful experimental verification of the Tokamak exhaust processing concept of iter with the caper facility

One of the design targets for the Tokamak Exhaust Processing (TEP) system of ITER is not to lose more than 10-5gh-1 into the Normal Vent Detritiation system of the Tritium Plant. The plasma exhaust gas therefore needs to be processed in a way that a tritium removal efficiency of about 108 with respect to the flow rate is achieved. Expressed in terms of tritium concentrations this corresponds to a decontamination from about 130 gm-3 down to about 10-4 gm-3 (about 1 Cim-3 = 3.7*1010 Bqm-3). The three step reference process for the TEP system of ITER is called CAPER and has been developed and realized at the Tritium Laboratory Karlsruhe (TLK). After the successful commissioning of the PERMCAT reactor as the key component of the third step detailed parametric tritium testing of the 3 steps involving the processing of more than 300 g tritium has been carried out and decontamination factors beyond the design requirements have been demonstrated for each process step and for the process as a whole. Not only the decontamination factor of 108 as required by ITER, but also the operational mode of TEP as a waste dump for gases from diverse sources has been experimentally validated with the CAPER facility.

Experience gained during the modification of the Caprice system to Caper

Abstract The experimental facility Caprice was designed to comply with the requirements for clean-up of tokamak exhaust gases. In the last 3 years simulated fusion exhaust gases containing 7 g of tritium have been processed with this facility achieving detritiation factors of up to 106. New requirements specifying detritiation factors of about 108 triggered the addition of a further tritium recovery step to the two already existing process loops. The main component of the third step is the so-called Permcat, a permeator–catalyst combination designed for isotopic swamping in a counter current mode. The upgrade of Caprice to the new system is now called Caper and involved the replacement of highly contaminated pipe work and the installation of an additional glove box, which houses the new components for the third loop as well as further equipment needed for the continuous operation of Caper.

Caper Modifications and First Experimental Results on Highly Tritiated Water Processing with PERMCAT at the Tritium Laboratory Karlsruhe

Abstract The CAPER facility operated at the Tritium Laboratory Karlsruhe for the demonstration of the tokamak exhaust processing system comprises a PERMCAT reactor as final clean-up stage. CAPER has been upgraded to enable the production of highly tritiated water (HTW) to be detritiated with PERMCAT. A staged approach for HTW production in CAPER is ongoing, using currently a metal oxide reactor, and later a micro-channel catalytic reactor. The whole experimental plan using the current single-tube PERMCAT reactor shall cover the HTW processing at flow rates up to 10 mL/min, with HTW up to 1.4 MCi/kg (i.e. stoichiometric DTO). The staged approach and corresponding CAPER modifications are described. The first experimental results obtained using metal oxide reactor are reported and discussed.

Tritium processing tests for the validation of upgraded PERMCAT mechanical design

Abstract The PERMCAT process, chosen for the final clean-up stage of the Tritium Exhaust Processing system in ITER, directly combines a Pd/Ag membrane and a catalyst bed for the detritiation of gaseous mixtures containing molecular and chemically bound tritium. Upgraded PERMCAT mechanical designs have been proposed to both increase the robustness and simplify the design of the reactor. One uses a special corrugated Pd/Ag membrane able to withstand change in length of the membrane during both normal operation and in the case of off-normal events. Based on this design, an upgraded PERMCAT reactor has been produced at FZK and successfully tested at TLK with ITER relevant tritiated gaseous mixtures using the CAPER facility.

Development of specific catalysts for detritiation of gases by counter current isotopic swamping

ABSTRACT The principal techniques developed by different research groups for the detritiation of primary gaseous wastes are altogether based on processes with multiple stages comprising at least one step involving heterogeneously catalyzed chemical reactions. While the permeation of hydrogen isotopes through palladium/silver membranes combined with heterogeneously catalyzed reactions were proven to be particularly suitable for highly contaminated gases, isotopic swamping in a counter current mode is the method of choice in ITER for the final detritiation and recovery of residual amounts of tritium. Since the catalyst employed to promote the isotope exchange reactions should not support methanation of carbon monoxide and carbon dioxide an attempt was made to design a highly selective exchange catalyst. Amongst the catalysts screened with methane - deuterium exchange and carbon oxide - methanation as test reactions a high temperature reduced palladium/silica (SiO2) catalyst was found to match the selectivity requirements. However, even though the palladium/silica catalyst shows very little activity for methanation, carbon monoxide was found to obstruct the isotope exchange reaction, whereas carbon dioxide does not show this unwanted effect.

Improvement and characterization of small cross-piece ionization chambers at the Tritium Laboratory Karlsruhe

Abstract At the Tritium Laboratory Karlsruhe stainless steel cross-piece ionization chambers have been used to measure the activity concentration of tritiated gases in experiments and processes for more than 10 years. New chambers with an optimized design in terms of the effective chamber volume were produced. Furthermore, they were gold and copper plated to determine the influence of the coatings on the signal and on the memory effect. A new chamber of the old design was built for direct comparison of the signals. The chambers were characterized with different helium-tritium mixtures in 8 runs and the ionisation current as a function of the static gas pressure was measured. When comparing the three new chambers, the gold chamber always showed the highest current, followed by the copper chamber. After exposing the chambers to ~13,100 TBq/m3, the memory effect was investigated by using a similar gas mixture of the earlier runs with ~1,500 TBq/m3. The gold chamber showed the highest memory effect, the copper chamber the lowest. This paper describes the design and the testing procedure of the chambers. It presents the first experimental results on the chamber performance, on the memory effects as well as calibration curves.

Experimental validation of main components of the Tokamak exhaust process for ITER-FEAT

The requirements of the tritium plant for ITER have been persistently detailed in the last decade and have led to increasing demands, especially for the Tokamak Exhaust Processing (TEP). Efficient multistage processes have been designed and commissioned to demonstrate the very high detritiation factors required. The operation of components installed at the Tritium Laboratory Karlsruhe, e.g. of a permeator run under the conditions expected for the front-end section of TEP (first stage), the development of catalysts for use in a Permcat (final (third) stage) which is a combination of a counter-current flow permeator and a catalyst to promote the exchange between tritium containing molecules and protium in the gas phase as well as results from decontamination of the methane cracker, key component of the second stage, after failure of both the main and redundant heater are described.

CAPER as Central and Crucial Facility to Support R&D with Tritium at TLK

Abstract The CAPER facility at TLK originally devoted to R&D on tokamak exhaust processing has been significantly upgraded over the last years. Beside new R&D on highly tritiated water, CAPER is presently largely used to support satellite experiments, mainly those dedicated to R&D on advanced analytics. Mutation from R&D to part of the TLK tritium infrastructure necessitated new features to be installed in order to facilitate and optimize tritiated mixtures preparation and sample filling, and to enable satellites experiments to discharge their waste gas to CAPER for clean-up. This paper presents recent CAPER mutations to become a central and key facility at TLK.

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.