[en] Within the framework of R&D studies linked to the development of Generation IV nuclear reactors, CEA has started to build up research helium loops. A dynamic helium loop dedicated to the purification of the helium is planned to be in operation at the end of 2007, and then connected with the dynamic helium technological loop called HELITE (1 MW) in 2009. In order to improve the data and knowledge, the CIGNE loop is dedicated to the preliminary tests on helium chemical purification processes foreseen for gas reactors. To control the chemical composition of impurities low level contents, it is needed to purify and to adjust the composition of the helium contained in the loop. Thus, it is necessary to study, at laboratory scale first, the best way to reach the requirements for future high temperature reactor. A loop allows analytical tests, to understand, select and choose most promising ways to purify helium coolant. This device devoted to chemistry studies has been built to consider impurities trapping and then reagents regeneration. The main components involved as impurities at ppm levels in this study are: H₂O ; CO ; H₂ ; CO₂ ; CH₄ ; O₂ ; N₂ ; NOx . This presentation is mainly focused on hydrogen and carbon monoxide elimination. Oxidation mechanisms and kinetics are studied using copper oxide as a reagent but, in the future, other oxides will have to be considered.

[en] Highlights: • Experimental results for the conversion of tritiated water (using deuterium as a simulant of tritium) by means of a catalytic membrane reactor in view of tritium recovery. • Phenomenological 2D model to represent catalytic membrane reactor behavior including the determination of the compositions of gaseous effluents. • Good agreement between the simulation results and experimental measurements performed on the dedicated facility. • Explanation of the unexpected behavior of the catalytic membrane reactor by the modeling results and in particular the gas composition estimation. - Abstract: In the framework of tritium recovery from tritiated water, efficiency of packed bed membrane reactors have been successfully demonstrated. Thanks to protium isotope swamping, tritium bonded water can be recovered under the valuable Q_2 form (Q = H, D or T) by means of isotope exchange reactions occurring on catalyst surface. The use of permselective Pd-based membrane allows withdrawal of reactions products all along the reactor, and thus limits reverse reaction rate to the benefit of the direct one (shift effect). The reactions kinetics, which are still little known or unknown, are generally assumed to be largely greater than the permeation ones so that thermodynamic equilibriums of isotope exchange reactions are generally assumed. This paper proposes a new phenomenological 2D model to represent catalytic membrane reactor behavior with the determination of gas effluents compositions. A good agreement was obtained between the simulation results and experimental measurements performed on a dedicated facility. Furthermore, the gas composition estimation permits to interpret unexpected behavior of the catalytic membrane reactor. In the next future, further sensitivity analysis will be performed to determine the limits of the model and a kinetics study will be conducted to assess the thermodynamic equilibrium of reactions.

[en] Highlights: ► Catalytic palladium based membrane reactor is studied for ITER tritium waste management. ► Concentration polarization effect was highlighted by two-dimensional mass transfer model. ► Mass transfer resistance due to concentration polarization is reduced by the increase of fluid velocity. ► Concentration polarization phenomenon is enhanced by the decrease of non-permeable species content in the feed stream. -- Abstract: Tritium waste recycling is a real economic and ecological issue. Generally under the non-valuable Q₂O form (Q = H, D or T), waste can be converted into fuel Q₂ for a fusion machine (e.g. JET, ITER) by isotope exchange reaction Q₂O + H₂ = H₂O + Q₂. Such a reaction is carried out over Ni-based catalyst bed packed in a thin wall hydrogen permselective membrane tube. This catalytic membrane reactor can achieve higher conversion ratios than conventional fixed bed reactors by selective removal of reaction product Q₂ by the membrane according to Le Chatelier's Law. This paper presents some preliminary permeation tests performed on a catalytic membrane reactor. Permeabilities of pure hydrogen and deuterium as well as those of binary mixtures of hydrogen, deuterium and nitrogen have been estimated by measuring permeation fluxes at temperatures ranging from 573 to 673 K, and pressure differences up to 1.5 bar. Pure component global fluxes were linked to permeation coefficient by means of Sieverts’ law. The thin membrane (150 μm), made of Pd–Ag alloy (23 wt.%_Ag), showed good permeability and infinite selectivity toward protium and deuterium. Lower permeability values were obtained with mixtures containing non permeable gases highlighting the existence of gas phase resistance. The sensitivity of this concentration polarization phenomenon to the composition and the flow rate of the inlet was evaluated and fitted by a two-dimensional model

[en] Room temperature gamma irradiation at medium (1-100 kGy) or high (0.9-25 MGy) doses induces different radicals into pure or industrial poly(vinyl chloride) (PVC); the various ESR signals differ by their shapes and/or values of their g-factors and/or peak-to-peak widths but do not give precise information on the chemical structures of the different radicals as the spectra are only poorly resolved. However, looking at the ESR parameters of the different signals and their evolution during natural ageing of the samples, allows us to make correlations between the radio-induced lines in industrial PVC and the ones induced in pure PVC or in PVC additives. (authors)

[en] Highlights: • A new compression fitting for thin-walled tubes has been developed. • Pd-Ag tubes have been joined by using stainless steel adapters and inserts. • The design of the fitting has been carried out via a stress analysis. • Tests have verified the tightness after hydrogenation and thermal cycling. - Abstract: Pd-alloy membrane tubes are used for hydrogen isotopes separation in the fusion fuel cycle. The efficiency of these separation processes has been significantly increased by the adoption of thin-walled self-supported membrane tubes that exhibit high permeance and infinite selectivity to hydrogen. A critical aspect in the realization of Pd-based membrane devices (both separators and membrane reactors) is related to the joining of the thin-walled tubes to the membrane module. In this work, an innovative fitting of thin-walled tubes has been obtained by coupling two special stainless steel joints (a weld adapter and a sealing insert) that tighten the flared edge of the tube. In particular, the design of the compression fitting relies on the elastic deformation reserve of the conical edge of the sealing insert that is capable: i) to ensure the sealing of the joining also in presence of the expansion/contraction of the Pd-Ag alloy during the hydrogenation cycling, and ii) to compensate small irregularities of the thin-walled tube (thickness, circularity, etc.). The effectiveness of the new joining technique in terms of both hydrogen perm-selectivity and stability has been verified in preliminary permeations tests.