[en] Hydrogen permeation through nickel dense membrane applied to Sodium cooled Fast Reactors has been studied theoretically and experimentally. In order to investigate the coupling of nickel membrane with external gas and sodium flows, an analytical model based on mass transfer resistances is developed. A sensitivity analysis showed that, for enough thick membranes and high sodium velocities, the nickel resistance has the most important effect. A permeator prototype constituted of four Ni201 tubular membranes, has been designed: experimental tests at pilot-scale are carried out at different temperatures, gas pressures and flowrates, both in gas-vacuum and gas-sodium configuration. Results for permeation against vacuum demonstrate that hydrogen diffusion within the membrane is the limiting step, in accordance with previous literature results obtained for pure nickel permeation experiments. (author)

[en] In order to operate a Sodium Fast Reactor in reliable and safe conditions, the quality of the coolant must be mastered. The chemical control of sodium is performed versus the different chemical compounds: oxygen (corrosion control), hydrogen (detection of the sodium-water reaction) and to a lesser degree, carbon (carburization, decarburization phenomena).Furthermore, other detrimental effects could be avoided: plugging of narrow sections, loss of heat transfer efficiency in heat exchangers, contamination and dosimetry,... Oxygen and moisture are introduced mainly during handling operations; hydrogen is due to aqueous corrosion of the Steam Generator Unit and thermal decomposition of hydrazine, used to control the oxygen content in the water. The purification of oxygen and hydrogen is adequately performed thanks to cold traps and mainly due to the fact that the solubilities are nearly nil for temperatures close to the fusion point, i.e. 97.8 deg. C. This paper deals with the development of purification systems for the primary and intermediate circuits of an SFR. Based on previous studies related to the basic mechanisms of Na₂O and NaH crystallization and on operational feedback from French Reactors, new concepts of cold traps were developed for Superphenix and EFR. In order to design new cold traps, a new computer tool has been developed, predicting the location and the amount of impurities deposited on cold walls for NaH and on wire mesh packing for NaH and Na₂O. This model helps the engineer developing a preconceptual design and assists the operator in following the filling rate of the cold trap, thereby avoiding long experimental tests in sodium facilities and reducing the cost of cold trap qualification strategies. (authors)

[en] The work deals with the removal by slow pyrolysis of epoxy resin from samples of spent nuclear fuel embedded in this polymer. Beyond the nuclear field, epoxy resin removal by pyrolysis is a typical issue for the recovery of metals in electronic waste. The main objective is to find the optimal conditions to remove hydrogen in the residual solid waste, in order to avoid hydrogen production by radiolysis during storage and so to prevent any risk of overpressure and explosion. The condensable pyrolysis products (tar-water mixture) and the char were characterised and quantified by elemental analyses, while the permanent gases were quantified by gas chromatography. A data reconciliation method was applied to adjust the values of raw measurements in order to complete the mass balances for both C, H, O and N elements and pyrolysis products. After studying the impact of temperature on the pyrolysis balance, experiments on a pilot furnace were conducted at 450 °C, in the frame of a parametric study of the heating rate, argon gas flow rate, resin mass and plateau time. At fixed temperature, we show that the plateau time is the only significant parameter for minimizing the residual hydrogen content in the char.

[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] Within the framework of the dismantling of Sodium cooled fast neutron reactors (SFR) in France (PHENIX, SUPERPHENIX, RAPSODIE), several processes are under investigation regarding sodium disposal. One of them, called ELA (radioactive sodium waste treatment process), is based on the implementation of the sodium-water reaction, in a controlled and progressive way, to remove residual sodium mainly from the sodium purification systems called cold traps. This system contains, after draining, residual sodium and trapped impurities such as sodium oxide (Na₂O), sodium hydride (NaH) with traces of tritium (NaT). The hydrolysis of these various chemical species leads to the production of a liquid effluent, mainly composed of an aqueous solution of sodium hydroxide, and a gaseous effluent, mainly composed of an inert gas, hydrogen and steam. The tritium is present in both effluents. Within the gaseous effluent, it is expected to be released as HT form only. But, according to some experimental data gathered from tritiated sodium hydrolysis operations performed at the CEA in France, a non-negligible amount of tritium is released in the off-gas as HTO form (up to more than 90 % of the tritium found in the gaseous effluent). HTO being 10,000 times more radiotoxic than HT, a precise knowledge of the mechanisms governing the phase distribution of tritium is necessary to estimate the tritium distribution. Indeed, it will help designing the process needed to optimize the treatment of the offgas before its release into the environment. In order to develop a numerical model able to predict the chemical composition of each effluent, a phenomenological description of the hydrolysis of residual sodium performed in the conditions of ELA has been proposed and is described in this paper. To validate some of the hypotheses made in this phenomenological description, and with the aim to validate the model that will be based on this scenario, a series of experiments has been performed in a laboratory-scale hydrolysis process designed at the CEA Cadarache, France. The experimental device consists of a 2-liter cylindrical glass reactor into which small quantities of sodium containing tritium were hydrolyzed by water injected drop by drop. A chemical characterization of the effluents generated by the process will allow us to study the influence of several parameters on the tritium distribution. An analysis of the experimental results obtained during this study is provided in this paper. (authors)

[en] The thermal degradation behavior of a commercial epoxy resin, EpoFix (Struers), has been investigated by thermogravimetry (TG), differential thermal gravimetry (DTG), and differential thermal analysis (DTA) under nonisothermal conditions in an argon atmosphere. Different methods (Kissinger, Flynn-Wall-Ozawa (FWO), Friedman iso-conversion methods, and nonlinear least-squares (NLSQ) estimation method) have been used to analyze the thermal degradation process and determine the apparent kinetic parameters. The methods produce similar results in terms of activation energy estimations. Nevertheless, the NLSQ method has several advantages over the other methods in terms of both characterizing the activation energy and modeling the thermal degradation - i.e., including this model in a resin degradation process simulation. However, it is interesting to combine the NLSQ method with other iso-conversion methods: they can reflect the dependence and variability of the activation energies during pyrolysis processes, while providing a good starting point for a nonlinear procedure, especially with respect to the activation energy E. This work is the first step (apparent kinetic reaction) of complete simulation of experimental oven of degradation of epoxy resin coating of impregnate nuclear fuel sample. (authors)

[en] This paper presents a general methodology for exergy balance in chemical and thermal processes integrated in ProSimPlus^® as a well-adapted process simulator for energy efficiency analysis. In this work, as well as using the general expressions for heat and work streams, the whole exergy balance is presented within only one software in order to fully automate exergy analysis. In addition, after exergy balance, the essential elements such as source of irreversibility for exergy analysis are presented to help the user for modifications on either process or utility system. The applicability of the proposed methodology in ProSimPlus^® is shown through a simple scheme of Natural Gas Liquids (NGL) recovery process and its steam utility system. The methodology does not only provide the user with necessary exergetic criteria to pinpoint the source of exergy losses, it also helps the user to find the way to reduce the exergy losses. These features of the proposed exergy calculator make it preferable for its implementation in ProSimPlus^® to define the most realistic and profitable retrofit projects on the existing chemical and thermal plants. -- Highlights: ► A set of new expressions for calculation of exergy of material streams is developed. ► A general methodology for exergy balance in ProSimPlus^® is presented. ► A panel of solutions based on exergy analysis is provided to help the user for modifications on process flowsheets. ► The exergy efficiency is chosen as a variable in a bi-criteria optimization.

[en] Operating a Sodium Fast Reactor (SFR) in reliable and safe conditions requires mastering the quality of the sodium fluid coolant, regarding oxygen and hydrogen impurities contents. A cold trap is a purification unit in SFR, designed to maintain oxygen and hydrogen contents within acceptable limits. The purification of these impurities is based on crystallization of sodium hydride on cold walls and sodium oxide or hydride on wire mesh packing. Indeed, as oxygen and hydrogen solubilities are nearly nil at temperatures close to the sodium melting point, i.e., 97.8 C, on line sodium purification can be performed by cooling down liquid sodium flows and promoting crystallization of sodium oxide and hydride. However, the management of cold trap performances is necessary to prevent from unforeseen maintenance operations, which could induce shut-down of the reactor. It is thus essential to understand how a cold trap fills up with impurities crystallization in order to optimize the design of this system and to overcome any problems during nominal operation. This paper deals with the mathematical modelling of crystallization process in a cold trap and predicts the location and the amount of the impurities deposit, on cold walls for sodium hydride and on wire mesh packing for sodium oxide. A model of the front propagation by 'diffuse deposit interface method' was developed and sensitivity to various parameters was evaluated. These results will enable to understand the consequences of the impurities deposited on the hydrodynamics and heat transfer in a cold trap. (authors)