a b s t r a c t
Development of a technico-economic optimization strategy of cogeneration systems of electricity/hydro- gen, consists in finding an optimal efficiency of the generating cycle and heat delivery system, maximiz- ing 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 MUL- TIGEN 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 opti- mized: the exchange surface, the exergy destruction and the number of exchange modules.
One of the great motivations of studying and developing Generation IV (GenIV) reactors of VHTR (Very High Temperature Reactor) design concept is their capacity to efficiently produce both electricity and H 2 (hydrogen). This study aims at developing an
optimization methodology for cogeneration systems of H 2 and electricity, from GenIV
In systems engineering, the availability of a system is its ability to be ready to achieve its required mission in defined operational conditions, assuming that required resources and existing support means are present . In order to comply with this key operational requirement, the NFM system has to be both reliable and maintainable, that is capable of achieving a continuous mission and undergoing modifications and repairs, respectively. A system with these capabilities is said to feature dependability. In addition, the nuclear safety of a nuclear reactor is actually another dependability requirement, which is called innocuity in systems engineering .
One of the great motivations of studying and developing Generation IV (GenIV) reactors of VHTR (Very High Temperature Reactor) design is their capacity
to efficiently produce both electricity and H 2 (hydrogen). This study aims at
developing an optimization methodology for cogeneration systems of hydrogen and electricity, with respect to energy constraints, economics and conjuncture in terms of demand. It lies within the scope of a collaboration between the Laboratoire de Génie Chimique (LGC Toulouse, France) and the French Atomic Energy Commission (CEA, Cadarache, France) in order to compare various cogeneration systems from both energy and economics viewpoints.This paper describes the different steps of the technico-economic methodology for
GEN-IV reactors aim to exhibit at least the same safety standards as the previous generation and also provide significant advances in future designs. Firstly, the uranium resource, just as the classical energy resources oil or gas, has a limited stock. According to some experts, it is limited to approximate hundreds years consumption with current nuclear reactor systems. So the fast neutron reactor technology, which falls under the aegis of GEN-IV reactors, could extend the utilization of the uranium reserves till several thousand years. Secondly, the nuclear waste management is an embarrassing issue and provokes certain conflicts concerning the potential safety risk. Gen-IV reactors aim to solve this issue by burning a large part of the long-live nuclear wastes, thereby reducing their volume as well as their toxicity. The GEN-IV reactors continue to make efforts to im- prove the safety of the installation facilities to reduce the risks and potential consequences of an accident while remaining economically viable. Lastly, they provide an unattractive and least desirable route for diversion and theft of weapon-usable materials and hence are resistant to nuclear proliferation. Six types of reactors are proposed and being studied by the researchers from different partner countries participating in the Gen-IV forum. France has chosen to go on with sodium cooled fast reactors mainly because of the maturity of the SFR concept, available know-how, prior experience in the country with reactors such as HARMONIE, RAPSODIE, PH ´ ENIX, SUPERPH ´ ENIX, consistency with the strategic national objectives of closed fuel cycles and long lived waste management. France, being
Traditionally, the analysis of nuclear system behaviour is performed using system thermal-hydraulics codes. Such analyses are validated using integral design speci ﬁc experiments or reactor data from prototype, test, or demonstration reactors. In recent years, the traditional approach of using system thermal-hydraulic codes is supplemented with new multi-scale approaches in which system thermal hydraulics codes are coupled to detailed three-dimensional CFD approaches. SESAME project aimed at extending the validation base by providing reference data at different levels. The validation data were provided in loop scale by experiments in the NACIE-UP facility, focused on the multi-scale coupling of the behaviour in the fuel assemblies and the loop system. Scaling up, the CIRCE facility in the so-called HERO con ﬁguration is used to provide experimental validation data. Real reactor data were provided from the Phénix reactor end of life tests. This data allowed validation of the three-dimensional effects to a much larger extent than the natural circulation test data which were previously used. Finally, the approaches under development will be applied to the MYRRHA and ALFRED lead-cooled reactor designs.
For ASTRID SFR project, this consideration was taken into account at the very beginning of the reactor conceptual design.
The topic was a particularly difficult one because: - how to take action on the reliability of the entire plant while studies on the sub-systems are only in their early stages?
Figure 5: Graph of the score for concept capability for prevention and mitigation
Some parameters and some criteria resulting from these parameters are proposed in this paper in order to assess without performing extensive studies, the capability of the reactor to prevent and to mitigate severe accidents. These parameters and criteria take into account the reactor concept features related to its core, its coolant, its overall geometry and its confinement options. They do not consider the safety provisions implemented through the detailed design process. So these criteria do not highlight the safety level of a concept but only its safety characteristics by roughly considering the possible physical behavior of the concept without prevention systems and mitigation measures. Thus, it can help to compare weak points of a concept and to provide an idea of accident sequences to be prevented and of physical effects to be mitigated. Their application to 3 concepts of GenIV reactors and to a PWR 1300 (Gen II) has enabled to show the relevancy of the criteria because the results of the present analysis cope with the results of detailed studies available for the 4 concepts. The proposed analysis can be used in the future in order to help the decision for design choices when starting a new design. Another potential purpose could be to improve prevention and mitigation capabilities during the design process on bad scored issues highlighted by the overall indicators proposed in this paper.
1. FUTURE NUCLEAR POWER: THE CHALLENGE
Nuclear power plant technology in the U.S. can be characterized as three distinct design generations: (1) prototypes, (2) current operating plants, and (3) advanced light water reactors. While the third generation plants have been very successful where they have been built in Europe, Asia and the Pacific Rim, further evolution is needed to make new nuclear energy systems a more attractive option for deployment around the world. In particular, the next generation of nuclear energy systems must be able to be licensed, constructed, and operated in a manner that will provide a competitively priced supply of energy while satisfactorily addressing plant reliability, nuclear safety, waste disposal, proliferation resistance, and public perception concerns of the countries in which they are deployed. Advanced water-cooled-reactor nuclear energy system concepts have been identified as part of the Generation IV International Roadmap evaluation  and R&D planning activity; i.e., involving international laboratories, academia, and industry groups from countries including Argentina, Brazil, Canada, France, Italy, Japan, Korea, Russia, Switzerland, the UK and the U.S. This activity resulted in the proposal of over thirty-eight specific reactor designs. For our purposes, the leading reactor designs can be categorized into two general groups:
DISCUSSION ON FUTURE TOPICS
Several aspects of multipactor-induced breakdown remain to be investigated in fusion RF systems. First of all, multipactor modelling work in the literature mostly concentrates on matched or low Voltage Standing Wave Ratio (VSWR) RF systems, which is the most frequent case in telecommunication satellite payloads. However, fusion RF antennas have to deal with a non-negligible part of the power reflected by the plasma. High VSWR can have an indirect effect on the multipactor threshold by peaking the electric field strength on several locations in the system and breakdown may appear at lower power level than initially assumed with matched models. Relationships between the plasma coupling properties with respect to the maximum power/electric field have to be established in order to help predicting the performances of the future large RF systems such as the ones of the ITER tokamak. Moreover, dielectrics like ceramics are used for the vacuum window materials in both ICRH and LHCD systems. These materials, mainly alumina or Beryllium oxide or eventually CVD diamond, have a high secondary emission yield and anti-multipactor treatments must be applied on them in order to allow high power handling. Future work will focus on the multipactor modelling of complex and multi-materials geometries with different secondary emission properties, with or without presence of inhomogeneous DC magnetic field in order to investigate the cyclotron resonance aspects in realistic environment.
Received 2 March 2004 / Accepted 13 October 2004
Abstract. In the framework of the methods we introduced for the restoration of images of Fizeau interferometers such as the Large Binocular Telescope, we propose an algorithm which is able to super-resolve compact stellar objects such as a binary system with an angular separation smaller than the angular resolution of the telescope. The method, which works also in the case of a monolithic mirror, is based on a simple modification of the Richardson-Lucy (RL) method or of the Ordered Subsets – Expectation Maximization (OS-EM) method for image deconvolution. In general, it consists of three steps: the first one requires a large number of RL-iterations, which are used to identify and estimate the domain of the unresolved object; the second one is a RL-restoration initialized with the mask of the domain. These two steps can provide a super-resolved image of the stellar system but the photometry of the stars may not be correct. Therefore their positions are derived from the result of the first two steps while their magnitudes are estimated in a third step by solving a simple least-squares problem. In order to show that the method can work in practice, we use (simulated) adaptive-optics-corrected point spread functions (PSF), both in the case of a monolithic and in the case of a binocular telescope, and we investigate mainly the case of binary systems. We analyze the limitations of the method in evaluating the angular separation and the relative magnitude of the two stars. The results we obtain are quite promising.
Helium implantation from transmutation reactions is a major cause of embrittlement and dimensional instability of structural components in nuclear energy systems. Development of novel materials with improved radiation resistance, which is of the utmost importance for progress in nuclear energy, requires guidelines to arrive at favorable parameters more efficiently. Here, we present a methodology that can be used for the design of radiation tolerant materials. We used synchrotron X-ray reflectivity to nondestructively study radiation effects at buried interfaces and measure swelling induced by He implantation in Cu/Nb multilayers. The results, supported by transmission electron microscopy, show a direct correlation between reduced swelling in nanoscale multilayers and increased interface area per unit volume, consistent with helium storage in Cu/Nb interfaces in forms that minimize dimensional changes. In addition, for Cu/Nb layers, a linear relationship is demonstrated between the measured depth-dependent swelling and implanted He density from simulations, making the reflectivity technique a powerful tool for heuristic material design. V C 2014 AIP Publishing LLC. [ http://dx.doi.org/10.1063/1.4883481 ]
54 Laurane Léost et al.
Since the discovery of nuclear fission in the middle of the 20th century, ac- tinide elements have been studied continuously. This family of unstable el- ements, of which uranium and plutonium are the two most famous repre- sentatives, has marked the history of science and humanity. Currently ura- nium and plutonium are strategic resources exploited at an industrial level. Schematically, these two radioactive elements are used for the production of electrical energy and for the manufacture of atomic weapons. The past use of nuclear weapons (atmospheric and submarine tests, Hiroshima and Na- gasaki bombs) and industrial nuclear accidents (Chernobyl, and Fukushima mainly) have resulted in significant environmental pollution and human contamination. In the current context, the risk of actinide dispersion is still present, and possible cases of internal contamination may mainly affect nu- clear workers or soldiers.
En utilisant le programme ABINIT, l'ensemble de ces études est basé sur la LDA (l'approximation de la densité locale) associée à la DFT (la théorie de la fonctionnelle de densité).
Les propriétés structurales (Le paramètre de maille, le module de rigidité et sa dérivée), mécaniques (constantes élastiques, module de cisaillement, le coefficient de Zener, le coefficient de Poisson, et le module de Young), vibrationnelles (Le spectre des phonons et leurs fréquences le long des différentes lignes de symétrie Γ, X , et L), et thermodynamiques (température de Debye, l’énergie libre, l’énergie interne, l’entropie, et la capacité thermique) des composées semiconducteurs SiX ( X= C, Ge) du type IV-IV, ainsi que leurs alliages binaires ont été calculées en utilisant la méthode VCA (virtual crystal approximation) et celle de la supercellule SC.
In Table 3, real data recorded for nuclear power in 2008 shows that the average is of 172 MWh/2 for the downward variation and of 190 MWh/2 for the upward variation. These levels increase by 2030 in EC 2030 case to 468 MWh/2 and to 461 MWh/2 respectively. For ramping rates higher than the level chosen for these simulations (1%), the wind power variability would increase the speed of up- and down-ward variations as shown in the Annexe 1. For instance, if ramp rates are allowed to be lifted toward ± 6%, the number of ramping events becomes more distributed over the range of ramp rates (i.e., 0- 1%, 1-2%, etc.). This implies that a more flexible nuclear system would be more effective at reducing the variable supply. By 2030, the load factor increase from 78% in 2008 to 90% which enhances a less flexible nuclear power system. Figure 2 shows the system reaction during the same day as in Fig 1, but considering no ramping constraints on nuclear reactors.