Abstract
Dense self-supported Pd-alloy membranes are used to selectively separate hydrogen and hydrogen isotopes. In particular, deuterium (D) and tritium (T) are currently identified as the main elements for the sustainability of the nuclear fusion reaction aimed at carbon free power generation. In the fusion nuclear reactors, a breeding blanket produces the tritium that is extracted and purified before being sent to the plasma chamber in order to sustain the fusion reaction. In this work, the application of Pd-alloy membranes has been tested for recovering tritium from a solid breeding blanket through a helium purge stream. Several simulations have been performed in order to optimize the design of a Pd-Ag multi-tube module in terms of geometry, operating parameters, and membrane module configuration (series vs. parallel). The results demonstrate that a pre-concentration stage before the Pd-membrane unit is mandatory because of the very low tritium concentration in the He which leaves the breeding blanket of the fusion reactor. The most suitable operating conditions could be reached by: (i) increasing the hydrogen partial pressure in the lumen side and (ii) decreasing the shell pressure. The preliminary design of a membrane unit has been carried out for the case of the DEMO fusion reactor: the optimized membrane module consists of an array of 182 Pd-Ag tubes of 500 mm length, 10 mm diameter, and 0.100 mm wall thickness (total active area of 2.85 m2).
Highlights
Nuclear fusion power is one of the most challenging and promising options for future carbon-free energy production
This work exhibits the results of a preliminary design of a Pd-alloy membrane diffuser for tritium extraction from the He purge stream of a helium cooled pebble bed (HCPB) breading blanket
By introducing a membrane diffuser directly downstream of the cold trap, a preliminary study has shown that a diffuser consisting of self-supported membranes could not efficiently treat the stream coming from the breeding blanket because of its very low tritium concentration
Summary
Nuclear fusion power is one of the most challenging and promising options for future carbon-free energy production. ITER is the halfway reactor aimed at assessing various plasma configurations, operational procedures, and technologies in view of DEMO The latter is currently being designed, and it will be the first demonstrative fusion power plant. In the fusion fuel cycle, membrane technologies are applied for processing tritiated streams of breeding blankets, plasma exhaust treatment, and water detritiation facilities. Metal dense membranes demonstrate good stability, which is another important requirement for safe operation in the nuclear plant Due to all these considerations, dense Pd-Ag membranes are currently the most used technology for separation processes in fusion fuel. Aof preliminary the required permeation area andthe of the particular, feasibility a Pd-basedassessment multi-tubeof diffuser for tritium extraction from He other is provided under different operating purgedesign gas hasparameters been evaluated. Required permeation area and of the other design parameters is provided under different operating scenarios
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