Multiobjective genetic algorithm strategies for electricity production from generation IV nuclear technology

Development of a technico-economic optimization strategy of cogeneration systems of electricity/hydrogen, consists in finding an optimal efficiency of the generating cycle and heat delivery system, maximizing the energy production and minimizing the production costs. The first part of the paper is related to the development of a multiobjective optimization library (MULTIGEN) to tackle all types of problems arising from cogeneration. After a literature review for identifying the most efficient methods, the MULTIGEN library is described, and the innovative points are listed. A new stopping criterion, based on the stagnation of the Pareto front, may lead to significant decrease of computational times, particularly in the case of problems involving only integer variables. Two practical examples are presented in the last section. The former is devoted to a bicriteria optimization of both exergy destruction and total cost of the plant, for a generating cycle coupled with a Very High Temperature Reactor (VHTR). The second example consists in designing the heat exchanger of the generating turbomachine. Three criteria are optimized: the exchange surface, the exergy destruction and the number of exchange modules

Optimization of electricity / hydrogen cogeneration from generation IV nuclear energy systems

One of the great motivations of studying and developing Generation IV (Gen IV) reactors of VHTR (Very High Temperature Reactor) design concept is their capacity to efficiently produce both electricity and H2 (hydrogen). This study aims at developing an optimization methodology for cogeneration systems of H2 and electricity, from Gen IV nuclear reactors, with respect to energy constraints, economics and conjuncture in term of demand. It lies within a scope of a collaboration between the Laboratoire de Génie Chimique (Toulouse, France) and the Commissariat à l’Energie Atomique (CEA, Cadarache, France) in order to compare various cogeneration systems from both energy and economics viewpoint. This paper presents the results of an optimization study based on the “minimal destruction of exergy” or “exergy loss” concept. This criterion, used within the framework of a mono-objective genetic algorithm optimizer, was applied successfully to electric and heat production from Gen IV systems

Experimental study of the tritium distribution in the effluents resulting from the sodium hydrolysis

Within the framework of the dismantling of fast breeder reactors 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 sodium contains impurities such as sodium hydride, sodium oxide and tritiated sodium hydride. 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 nitrogen (inert gas), hydrogen and steam. The tritium is distributed between these effluents, and, within the gaseous effluent, according to its forms HT and HTO. HTO being 10,000 times more radiotoxic than HT, a precise knowledge of the mechanisms governing the phase distribution of tritium is necessary. Indeed, it will help to design the process needed to optimize the treatment of the off-gas before its release into the environment. This paper presents the first experimental results from a parametric study on the tritium distribution between the various effluents generated during hydrolysis operations. This parametric study has been performed in a laboratory scale hydrolysis process designed at the CEA Cadarache

Experimental study of the tritium distribution in the effluents resulting from the sodium hydrolysis

Within the framework of the dismantling of fast breeder reactors 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 sodium contains impurities such as sodium hydride, sodium oxide and tritiated sodium hydride. 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 nitrogen (inert gas), hydrogen and steam. The tritium is distributed between these effluents, and, within the gaseous effluent, according to its forms HT and HTO. HTO being 10,000 times more radiotoxic than HT, a precise knowledge of the mechanisms governing the phase distribution of tritium is necessary. Indeed, it will help to design the process needed to optimize the treatment of the off-gas before its release into the environment. This paper presents the first experimental results from a parametric study on the tritium distribution between the various effluents generated during hydrolysis operations. This parametric study has been performed in a laboratory scale hydrolysis process designed at the CEA Cadarache

Characterization of the reactive system involved in the high temperature treatment of tar and gas coming from biomass pyrolysis

This work contributes to the on going emergence of new technologies for energy production. It deals with the use of lignocellulosic biomasses to produce syngas that can be transformed into synthetic fuel by the Fischer Tropsch process. A two-stage process is studied performing first the biomass pyrolysis then the catalytic treatment of the produced gas at 1000°C. The objective of this study is to better understand the physical and chemical phenomena involved during the high temperature gas treatment stage through a coupled experimental and modelling approach. A particular attention is paid to the removal of tar produced during the first stage, and to the opportunity of using the char produced during the biomass pyrolysis as catalyst in the second stage. A phenomenological model describing the system (geometry, heat transfer, mass transfer between the different phases (gas, tar, char) and throughout the bed) has to be developed. The tar and the char compositions and potential interactions are particularly complex. Indeed, the tar is a lump of a hundred compounds and in addition, the reaction network is rather complex: decomposition reactions (steam and dry reforming, cracking), polymerisations, soot formation and interactions between the compounds. So some “model compounds” illustrating some of the characteristics of the whole group or the limit of these characteristics (i.e. the steam reforming reactivity, the thermal stability…) have been selected to simplify the reaction network. In order to establish the basis of the phenomenological model, some preliminary experiments are carried out on the Biocarb facility to study the behaviour of the first stage and the destruction of tar on different loads

Modelling of a hydrogen permeation process from gas phase towards liquid sodium and experimental set-up for prototype testing

International audienceHydrogen 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

Exergy analysis for Generation IV nuclear plant optimization

This article deals to the application of exergy concept to the energy production system involving a VHTR (Very High Temperature Reactor) coupled with an innovative electricity-generating cycle. The objective is to propose a general formulation to quantify the exergy destruction of the involved process components embedded in a thermodynamic simulator CYCLOP (Haubensack, 2004). The exergy destruction is thus identified as a major criterion to minimize. For this purpose, a genetic algorithm embedded in the so-called MULTIGEN environment is used. Finally, the optimization criterion, based on exergy destruction minimization, is applied to electrical production by a Brayton-Rankine combined cycle connected to a nuclear reactor. Some typical results are presented. The perspectives of this work including the cogeneration of hydrogen and electricity are highlighte

Radial viscous fingering in miscible Hele-Shaw flows: A numerical study

A modified version of the usual viscous fingering problem in a radial Hele-Shaw cell with immiscible fluids is studied by intensive numerical simulations. We consider the situation in which the fluids involved are miscible, so that the diffusing interface separating them can be driven unstable through the injection or suction of the inner fluid. The system is allowed to rotate in such a way that centrifugal and Coriolis forces come into play, imposing important changes on the morphology of the arising patterns. In order to bridge from miscible to immiscible pattern forming structures, we add the surface tensionlike effects due to Korteweg stresses. Our numerical experiments reveal a variety of interesting fingering behaviors, which depend on the interplay between injection (or suction), diffusive, rotational, and Korteweg stress effects. Whenever possible the features of the simulated miscible fronts are contrasted to existing experiments and other theoretical or numerical studies, usually resulting in close agreements. A number of additional complex morphologies, whose experimental realization is still not available, are predicted and discussed. © 2008 The American Physical Society

Glycosylphosphatidylinositol Anchors from Galactomannan and GPI-Anchored Protein Are Synthesized by Distinct Pathways in Aspergillus fumigatus

Glycosylphosphatidylinositols (GPIs) are lipid anchors allowing the exposure of proteins at the outer layer of the plasma membrane. In fungi, a number of GPI-anchored proteins (GPI-APs) are involved in the remodeling of the cell wall polymers. GPIs follow a specific biosynthetic pathway in the endoplasmic reticulum. After the transfer of the protein onto the GPI-anchor, a lipid remodeling occurs to substitute the diacylglycerol moiety by a ceramide. In addition to GPI-APs, A. fumigatus produces a GPI-anchored polysaccharide, the galactomannan (GM), that remains unique in the fungal kingdom. To investigate the role of the GPI pathway in the biosynthesis of the GM and cell wall organization, the deletion of PER1—coding for a phospholipase required for the first step of the GPI lipid remodeling—was undertaken. Biochemical characterization of the GPI-anchor isolated from GPI-APs showed that the PER1 deficient mutant produced a lipid anchor with a diacylglycerol. The absence of a ceramide on GPI-anchors in the Δper1 mutant led to a mislocation of GPI-APs and to an alteration of the composition of the cell wall alkali-insoluble fraction. On the other hand, the GM isolated from the Δper1 mutant membranes possesses a ceramide moiety as the parental strain, showing that GPI anchor of the GM follow a distinct unknown biosynthetic pathway