1,720,998 research outputs found
Preliminary results from a detritiation facility dedicated to soft housekeeping waste and tritium valorization
No full textNuclear waste management has to be taken into account for fusion machine using tritium as fuel. Soft housekeeping waste (e.g. gloves, tissues, protective clothes, etc.) is produced during the whole life as well as during the dismantling of the reactor and is contaminated by tritium under reduced (HT) and oxidized (HTO) forms. In collaboration with ENEA, a lab-scaled facility has been built at CEA Cadarache for soft housekeeping waste detritiation and tritium valorization. The previously milled waste is placed in a reactor to be heated up to a temperature lower than the housekeeping melting point. A carrier gas is then injected in the detritiation reactor to remove tritium, thanks to the combined effects of temperature and carrier gas (type and feed flow). The tritiated gas exhausted from the detritiation reactor is then sent through a catalytic Pd-Ag membrane reactor (CMR) where tritium is recovered via isotopic exchange reaction and permeation phenomenon. Based on previous studies that have allowed defining the most efficient operating conditions for the detritiation process, this work presents the results obtained by the coupling of the detritiation facility with the CMR. Due to safety considerations, restrictions on the nature of the carrier gas were applied, rejecting air as the carrier gas even though air was the best candidate for the detritiation part of the process. The performance of the whole system was estimated by means of a parametric study on the influence of flow rates in the CMR and transmembrane pressure. © 2014 Elsevier B.V
Multi-tube Pd-Ag membrane module for pure hydrogen production: Comparison of methane steam and oxidative reforming
No full textThe results of steam and oxidative reforming of methane carried out through a membrane system are being compared in this work. The capability of the experimental setup to produce ultra-pure hydrogen has been evaluated in terms of hydrogen yield under different operating conditions. The reforming reactions took place over a Pt on Al2O3 catalyst in a traditional high temperature reformer, while the hydrogen produced has been removed by selective permeation in a membrane module containing an array of 19 defect-free Pd-Ag tubes (length 250 mm, diameter 10 mm and wall thickness 0.150 mm). The reformer has been tested in the temperature range of about 570-720 C while the membrane module temperature has been maintained at 350 C and the reaction (lumen) pressure has been ranged between 100 and 500 kPa. Methane feed flow rates from about 0.4 × 10-3 to 1.1 × 10-3 mol s-1 have been fed into the reformer with methane/water molar ratios of 1/4 and methane/water/oxygen of 1/3/0.33 for the steam and the auto-thermal reforming, respectively. A maximum hydrogen yield value of 2.8 corresponding to a hydrogen flow rate of 1.20 × 10-3 mol s-1 has been measured during the methane steam reforming at pressure of 350 kPa, GHSV of 864 L(STP) kg-1 h-1 and reformer temperature of 700 C. © Copyright © 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved
Reliability and availability requirements analysis for DEMO: Fuel Cycle system
No full textTwo of the key elements of the engineering development of the DEMO reactor are the definitions of reliability and availability requirements (or targets). The availability target for a hypothesized Fuel Cycle has been analysed as a test case. The analysis has been done on the basis of the experience gained in operating existing tokamak fusion reactors and developing the ITER design. Plant Breakdown Structure (PBS) and Functional Breakdown Structure (FBS) related to the DEMO Fuel Cycle and correlations between PBS and FBS have been identified. At first, a set of availability targets has been allocated to the various systems on the basis of their operating, protection and safety functions. 75% and 85% of availability has been allocated to the operating functions of fuelling system and tritium plant respectively. 99% of availability has been allocated to the overall systems in executing their safety functions. The chances of the systems to achieve the allocated targets have then been investigated through a Failure Mode and Effect Analysis and Reliability Block Diagram analysis. The following results have been obtained: i) the target of 75% for the operations of the fuelling system looks reasonable, while the target of 85% for the operations of the whole tritium plant should be reduced to 80%, even though all the tritium plant systems can individually reach quite high availability targets, over 90%-95%; ii) all the DEMO Fuel Cycle systems can reach the target of 99% in accomplishing their safety functions. © 2015, American Nuclear Society. All rights reserved
Pd-based membrane reactors for producing ultra pure hydrogen: Oxidative reforming of bio-ethanol
No full textA membrane reactor consisting of a dense self-supported Pd-Ag tube of wall thickness 60 μm has been filled with a Pt-based catalyst and used for producing pure hydrogen via oxidative steam reforming of bio-ethanol. The reformer feed stream consisted of water and ethanol with traces of glycerol and acetic acid in order to simulate a liquid waste of dairy industry after fermentation and concentration. The membrane reformer has been characterized through permeation and reaction tests performed at 400 and 450°C with a reaction (lumen) pressure in the range 100-200 kPa. The hydrogen permeated through the membrane has been collected in the reactor shell by a sweep stream of nitrogen. Permeation tests verified the complete hydrogen selectivity of the thin wall tube membrane and measured permeability values at 400-450°C of 1-2 mol m-1 s-1 Pa-0.5 accordingly to the literature. In the reaction tests, the capability of the membrane to promote the reaction conversion (shift effect) has been demonstrated. The gas chromatographic analysis of the retentate showed very low concentration of CO and the presence of methane as a main product of side-reactions. At 400°C the pressure affects significantly the hydrogen production and the hydrogen yield moves from 0.4 to 1 when the pressure increases from 100 to 200 kPa. Significant increase of the hydrogen production has been attained at the higher temperature of 450°C where maximum values of hydrogen yield (close to 3) have been measured with a lumen pressure of 200 kPa. Under these conditions, the technology of Pd-based membranes is effective for recovering hydrogen from a liquid waste. © 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved
Design, manufacturing and testing of Pd-membranes and membrane reactors for detritiation processes
No full textPd-based dense membranes are used to separate hydrogen isotopes with infinite selectivity. Membrane modules have been studied for several detritiation processes in the fuel cycle of fusion reactors: plasma exhaust treatment, tritium extraction from the breeding blanket and detritiation of highly tritiated water. © 2015 IEEE
Testing of dense Pd-Ag tubes: Effect of pressure and membrane thickness on the hydrogen permeability
No full textThe relevant role of hydrogen in the new and clean energy systems motivates the interest in membrane technologies able to separate and purify such element. Dense Pd-based membranes are particularly attractive for the high values of hydrogen selectivity and good permeance provided. An established approach to model the mass transfer of hydrogen through dense metal membranes describes permeation flux as proportional to the difference of the square root of the hydrogen partial pressure in the feed and permeated side divided by the inverse of the membrane thickness. However, deviations from this law are reported in literature especially when large range of pressure and membrane thickness are considered.This work presents the results of an experimental activity carried out on three dense, defect-free, self-supported Pd-Ag membranes having a thickness of 84, 150 and 200μm, respectively. During testing, the measurements of the hydrogen flux permeated through the membranes were collected in the pressure and temperature ranges of 200-800. kPa and 473-623. K, respectively. The observed permeability pre-exponential factors and activation energies exhibited a dependence on the pressure and the membrane thickness, in agreement with the square root formula mentioned above.This dependence has been discussed by investigating the impact of two effects on the considered process: the relationship between the hydrogen diffusivity from the H/Pd ratio and the surface reactions. The analysis reported in this work shows that Sieverts' law does not account for these two effects. In fact, when applying Sieverts law at the experimental data, a specific pattern is observed in the activation energy (Ea) of the hydrogen permeability. This fact is in contrast with the definition of permeability which is an intrinsic property of the material. © 2013 Elsevier B.V
Combined methane and ethanol reforming for pure hydrogen production through Pd-based membranes
No full textCombined methane and ethanol steam reforming has been carried out in a conventional reformer filled with a Pt (0.5% wt.) catalyst bed. The reformer has been coupled with a multi-membrane module, where pure hydrogen has been recovered in the shell side by vacuum pumping. The experiments-that mainly aimed at measuring the hydrogen yield-have been carried out in the reaction (lumen) pressure range of 100-500 kPa, while the temperature of the reformer and the Pd/Ag membranes module has been of 760°C and 350°C, respectively. The water/ethanol/methane molar ratio has varied in the different experiments (10/1/0, 11/1/0.25, 14/1/1 and 26/1/4). Such water/ethanol mixtures have been investigated in order to simulate the treatment of dilute bioethanol with methane. The hydrogen yield decreases when the molar ratio methane/ethanol increases while-in presence of a high water excess (feed molar ratio water/ethanol/methane of 26/1/4)- A hydrogen yield up to 35% at 500 kPa can be achieved. Copyright © 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved
Hydrogen permeation through Pd-Ag membranes: Surface effects and Sieverts' law
No full textMetal membranes mainly made of Pd alloys can be applied in membrane reformers for ultrapure hydrogen production from hydrocarbons and alcohols. Knowledge of the hydrogen mass transfer mechanisms through metals is very important to the purpose of properly designing and operating the membrane reactors. With the aim of understanding the deviations from the ideal behavior of the transport mechanisms predicted by the Sieverts' law, a permeation model which takes into account the surface effects has been applied to the permeability measurements that have been carried out on dense Pd-Ag permeator tubes from 473 to 623 K. The model has been validated by the results of permeation tests in a wide range of pressure (200-800 kPa) and membrane thickness (84-200 μm). The new model modifies the Sieverts' law by introducing the mass transfer resistances due to surface effects. The values of the surface resistance and permeability calculated by the model have been compared with the literature. Finally, the new hydrogen permeation expression has been applied in order to analyze the cost of a separation system which would consist of tubular Pd-based membranes. © 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved
The REX irradiation facility and its applications
No full textThe REX system is based on a linear electron accelerator and a removable head containing an electron to X-ray converter with its collimator. The machine and the irradiation chamber were manufactured and commissioned at ENEA Frascati Research Center. The activity of the Laboratory for Development of Particle Accelerators and Medical Applications is dedicated to the development of particle accelerators (electrons and protons) for medical, industrial and research applications, realized as sections of complex equipment or as stand-alone machine and offers related services to the scientific community. The REX facility is a versatile irradiation machine thought to be used for experimental campaigns in different research fields thanks to its customizable beam. Some of the cases we performed are related to irradiation of biological systems, development of in-beam monitoring devices, test of beam monitors, material radiation damage studies and cultural heritage. Experiments are carried out for specimen treatment with the two-radiation quality: electrons and X-rays. An overview of the laboratory and of the activities performed with the REX facility in its present status are given in this work and specific attention is devoted to the application on the cultural heritage for the preservation and conservation of artefacts
- …
