Accurate and easy to implement multi-scale modelling algorithm

Abstract

The Université Bretagne Sud has developed an algorithm in order to improve fusion plasma simulation (gyrokinetic and kinetic codes, turbulent transport) and especially reached problems of convergence of two-scale models. This project gave the way to transfer information between the various scales while attending simulating a multi-scale phenomenon. Conveniently used to tackle many phenomena involving oscillations or heterogeneities with high degree of accuracy, yet without requiring detailed input, this technology can find many applications in the study of complex fluidics, porous media flow and oscillatory dynamical systems.

Description of the Technology

Physical phenomena can be observed and simulated at different scales and degrees of complexity. Multiscale modelling consists in a framework, based on fundamental principles, for building mathematical and computational models of such phenomena, by examining the connection between models at different scales.

The technology consists in an algorithm especially designed to tackle the challenges of convergence of two-scale models widely used for fusion plasma. Tokamak and stellarator are toric devices in which a mixture of deuterium and tritium particles is heated and submitted to a strong magnetic field, in order to ignite a fusion reaction and extract the produced energy. It is well known that the trajectory of a charged particle in a magnetic field is a helix. The period of this helix, called the gyroperiod, depends only on the mass and charge of the particle, and on the magnitude of the magnetic field. As the magnitude of the magnetic field is nearly constant and as there are essentially three species of particles (deuterium, tritium, and electrons), the particle mixture performs oscillations with only a few frequencies, which are well separated from one another. Moreover, since in such devices the magnetic field is strong, those frequencies are high.

Two-scale convergence is efficient but challenging in tokamak or stellarator plasma physics. In addition, the two-scale convergence is the easiest homogenization approach to manipulate and efficiently handle many phenomena involving oscillations or heterogeneities without a lot of analytical material or requiring detailed input.

Innovation and advantages of the offer

The innovation introduced in the Pd-membrane reactors for fusion fuel cycle applications consists of innovative mechanical design concepts (multi-tube modules, heating systems, compact size) and new joining techniques of Pd-tubes to steel parts. These developments allow operating detritiation processes in a continuous mode (then more efficiently and safely than the alternative processes based on the use of traditional reactors or on selective absorption in batch operations). In the tests carried out at CEA Cadarache laboratories (EFDA task on JET soft housekeeping waste detritiation) where D2O was used instead of tritiated water, under the best operating conditions a Pd-membrane reactor exhibited very high extraction efficiency by recovering more than 90% of deuterium via isotopic exchange over the catalyst and permeation through the selective membrane.

Non fusion applications

Thanks to the validity of the technologies developed in the fusion, several applications in the field of (pure) hydrogen production (both membrane technology and process optimization) have been approached. Membrane reactors have been tested for the production of hydrogen and syngas from reforming of methane, ethanol and biomass. Reforming of olive mill wastewater via membrane processes allows to recover up to 3 kg of hydrogen per ton of wastewater. Although cost of Pd-alloy is still a hurdle in large scale applications, Pd-tubes can be applied in hydrogen generators for laboratory and other ultra-pure hydrogen devices. Furthermore, the processes based on dehydrogenation reactions represent the only solution available for some kind of biomass that cannot be treated via the conventional biological processes. This is the case of olive mill wastewater: the reforming process studied allows the reduction of the environmental pollution and its valorization for producing energy (hydrogen and syngas). Therefore, potential applications outside fusion concern: realization of small purifier for laboratory hydrogen generators, reforming of biomass for producing hydrogen and syngas. The technology and related know-how reach a TRL 8 in fusion and is available for demonstration in non-fusion.

EUROfusion Heritage

Researches at ENEA Frascati about Pd-membrane are carried out since 90’s years in the frame of the programmes EFDA and then EUROfusion and in collaboration with CEA Cadarache and KIT (former TLK) Institutes. In this field, ENEA developed a relevant expertise moving from material development (diffusion bonding of Pd-Ag sheet for realizing thin-wall permeator tubes), then designing innovative Pd-membrane reactor (single and multi-tube finger-like configurations, heating systems, Pd-tubes joining) and, finally, developing detritiation processes via membrane