Bolzano, Italy
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Tosti S.,ENEA | Rizzello C.,Tesi Sas | Borgognoni F.,ENEA | Ghirelli N.,CEA Cadarache Center | And 2 more authors.
Fusion Engineering and Design | Year: 2011

The development of a Pd-based membrane reactor to be applied in processes for tritium removal from various gaseous streams of tokamak systems has been carried out. In particular, the membrane reactor has been designed for decontaminating soft housekeeping wastes of JET. This membrane reactor consists of Pd-Ag permeator tube fixed in a finger-like mode into a stainless steel shell. The feed stream (gases to be detritiated) is fed inside the membrane lumen where the isotopic exchange takes place on to a catalyst bed while pure hydrogen (protium) is sent in countercurrent mode in the shell side. The feed stream consists of 200 Ncm 3 min -1 of helium with 10% of tritiated water (tritium content 1.11 × 10 8 Bq h -1). The membrane reactor design has been based on a simplified calculation model which takes into consideration the very low tritium content of the gas to be processed and the complete oxidation of the tritiated species in the feed stream. The model considers a tubular Pd-Ag membrane divided into finite elements where the mass balances are performed according to both the thermodynamic equilibrium reactions and permeation rates through the membrane of the hydrogen isotopes. The reactor model has permitted to verify that a Pd-Ag commercial tube of diameter 10 mm, length 500 mm and wall thickness 0.150 mm is capable to attain a decontamination factor larger than 10. A new mechanical design of the Pd membrane reactor has been also developed: especially, harmful mechanical stresses of the long permeator tube consequent to the hydrogenation and thermal cycling has been avoided. Furthermore, an innovative effective heating system of the membrane has been also applied. © 2011 EURATOM ENEA Association-ENEA Unit. Published by Elsevier B.V. All rights reserved.

Borgognoni F.,ENEA | Tostr S.,ENEA | Rizzello C.,Tesi Sas | Vadrucci M.,ENEA | And 2 more authors.
Fusion Science and Technology | Year: 2011

This paper presents a model and a simulation code which study a Pd-based membrane reactor for detritiating highly contaminated gas streams. A finite elements method has been applied for evaluating the mass balance equations taking into account the isotopic exchange reactions equilibrium and the permeation kinetics. The code has been validated by comparing the results of the inactive experiments carried out on a prototype Pd-Ag reactor where high D/H ratios have been used. Further, a parametric analysis for evaluating the effect of the temperature and membrane wall thickness on the water detritiation capability has been performed.

Tosti S.,ENEA | Basile A.,University of Calabria | Bettinali L.,ENEA | Borgognoni F.,Tesi Sas | Rizzello C.,Tesi Sas
Topical Conference on Hydrogen 2006, Held at the 2006 AIChE Spring National Meeting | Year: 2014

Thin wall Pd-Ag permeator tubes have been produced by a diffusion welding procedure: these low-cost membranes are proposed for separating and producing highpure hydrogen in membrane reactors. The reliability of these dense metallic permeators is strongly related to the design configuration of the membrane modules. In fact, as a consequence of hydrogen and thermal cycling, the dense metallic tubes vary their length: therefore, in case of constrains between the membrane and the module, cyclic axial stresses on the tube can rise and involve the rupture of the permeator. In our application, a fingerlike assembly of the membrane tubes inside the reactor has been designed: it permits the free elongation and contraction of the palladium alloy tube avoiding any mechanical cycling stress. A process in which a membrane reactor produces ultra pure hydrogen needed to feed a polymeric fuel cell of power 500 W has been designed: the process foresees the use of both traditional and membrane reactors. The membrane reactor consists of a bundle of Pd-Ag thin wall tubes operating in parallel where the water gas shift reaction takes place at 350°C and 200 kPa: the hydrogen stream of 4,46·10-3 mol s-1 (about 6 liter/min) permeating through the membrane is recovered in the shell side by means of nitrogen sweep gas at 100 kPa.

Rizzello C.,TESI Sas | Borgognoni F.,ENEA | Pinna T.,ENEA | Tosti S.,ENEA
Fusion Engineering and Design | Year: 2010

The tritium confinement strategy adopted during the past years in the ITER hot cell building is compared to the safety requirements given by the standard ISO-17873 "Nuclear facilities - criteria for the design and operation of ventilation systems for nuclear installations other than nuclear reactors". In fact, this is the reference safety guideline recommended by French licensing authorities. Several features of the considered design of the hot cell building are not in agreement with these guidelines. Main discrepancies concern the zoning of the hot cell complex, the flow rates of ventilation, and the possibility to recycle the room atmosphere and to detritiate the effluent air. These aspects are discussed together with some proposed modifications of the design. © 2009 Elsevier B.V. All rights reserved.

In a D-T fusion machine, due to the possible reaction between tritium and oxygen, some potential sources of highly tritiated water (HTW) can be identified. Therefore, a dedicated detritiation process has to be assessed either for economic and safety reasons. In this view, the use of a Pd-based membrane reactor performing isotopic exchange reactions can be considered since hydrogen isotopes exclusively permeate the Pd-Ag membrane and their exchange over the catalyst realizes the water detritiation. In this activity, the treatment of highly tritiated water, generated by an ITER-like machine (i.e. 2 kg of stoichiometric HTO containing up to 300 g of tritium), via a Pd-membrane reactor is studied in terms of decontamination capability. Especially, a parametric analysis of two processes (water gas shift and isotopic swamping) performed in a Pd-based membrane reactor is carried out by using two mathematical models previously developed and experimentally verified. Particularly, the effect of the reactor temperature, the membrane thickness, the reaction pressure and the protium sweep flow-rate is investigated. Moreover, a comparison in terms of the decontamination factor and the number of reactors necessary to detritiate the HTW are provided. Generally, the results reveal a higher decontamination capability of the WGS reaction respect with the IS (maximum DF values of about 120 and 1.6 in the case of WGS and IS, respectively). However some drawbacks, mainly related with the formation of tritiated species, can occur by performing the WGS. © 2013 Elsevier B.V.

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