1,720,966 research outputs found
Multiphysics Modelling of Fusion Machines Liquid-Breeder Blankets
Full text linkL'abstract è presente nell'allegato / the abstract is in the attachmen
Multiphysics modelling of the Activated Corrosion Products generation and transport in the WCLL PbLi loop with GETTHEM
Full text linkOne of the main milestones towards the development of the EU DEMO reactor is to demonstrate the feasibility of a closed tritium fuel cycle, a key aspect for the generation of electricity from fusion energy by the middle of the century. In view of this, the design of the breeding blanket (BB) has a key role. A candidate design for the EU DEMO BB is the Water-Cooled Lithium-Lead (WCLL) concept, where eutectic lithium-lead (PbLi) is circulated in a suitable closed circuit. A key issue in the design of the PbLi circuit is the evaluation of the inventories of Activated Corrosion Products (ACPs), which are solid particles corroded from structural materials and eventually activated in the blanket, transported inside the loop within the PbLi. In recent years, a PbLi loop model has been implemented in the GETTHEM code, a system-level tool for the thermal-hydraulic modelling of BB and related subsystems. In this work, in addition to the already existing assessment of corrosion phenomena, models of different pieces of physics necessary for a comprehensive assessment of the ACP inventories are added to the PbLi loop model in GETTHEM. Specifically, these include activation and decay of the corroded species in the BB. For the latter, a sink term for the radioactive decay and a source term for the transmutation due to neutrons interaction with materials are introduced in the mass conservation equations for each ACP. To demonstrate the code capabilities, a representative test case is presented
Monte Carlo modelling of the ARC Breeding Blanket with the Serpent code
No full textThe Affordable, Robust, Compact (ARC) fusion reactor, proposed by MIT, foresees the use of an innovative “liquid immersion” Breeding Blanket (BB), entirely constituted by a molten salt (FLiBe), serving all the BB functions (tritium breeder and carrier, neutron multiplier, coolant and shielding). Neutronic calculations have been carried out in the past with the Monte Carlo N-Particle (MCNP) transport code to estimate the Tritium Breeding Ratio (TBR), the power generation in the FLiBe, and the neutron flux to the magnets.
In the present work the Monte Carlo Serpent code, developed at VTT, is used to evaluate the TBR and power deposited in the ARC BB, as a first step towards a comprehensive neutronic analysis of ARC with Serpent, thus including other relevant aspects such as magnet shielding and material activation. Two different models for the neutron source generated by the plasma are used, starting from a spatially uniform neutron source, and then moving to a non-uniform distribution, more representative of the actual differences in neutron source generation in the plasma core with respect to the edge. Moreover, an estimation of the uncertainty of the results, associated with the uncertainty in the nuclear data, is performed, thanks to non-intrusive Uncertainty Quantification methods like Polynomial Chaos Expansion. The results are compared with those available in the open literature, proving the applicability of the Serpent code to the neutronic analysis of liquid immersion BBs
A Genetic-Driven Optimization of the Energy Grid Structure for Nodal Full-Core Calculations in Lead-Cooled Fast Reactors
No full textThis work presents a novel genetic algorithm (GA) for optimizing the few-group energy grid structure used for full-core nodal calculations in lead-cooled fast reactors. The optimization is started considering a set of group constants computed on a reference 61-group structure from which the GA selects an optimal subset of groups. Compared to existing works in the literature, the number of groups is not defined a priori but varies within a user-defined range, allowing a better exploration of the solution space. This feature requires one to develop an adequate representation of the chromosomes used in the evolution process, which is examined with different definitions of the chromosomes. The work also proposes a suitable combination of physics-driven fitness functions (FFs) related to the effective multiplication factor, the power density, and the neutron flux. Different weights based on the adjoint flux are also studied for the flux FF, with the aim of improving the convergence of the evolution process. All the studies are performed focusing on a three-dimensional model of the Advanced Lead Fast Reactor European Demonstrator (ALFRED) core design, which is modeled using the multigroup diffusion module of the Fast REactor NEutronics/Thermal-hydraulICs (FRENETIC) multiphysics code. The results suggest that the energy grid can be profitably optimized using a representation with two chromosomes. The optimal solutions yielded by the GA are justified on a physical basis by looking at some relevant figures of merit
Application of the Polynomial Chaos Expansion to the Uncertainty Propagation in Fault Transients in Nuclear Fusion Reactors: DTT TF Fast Current Discharge
Full text linkNuclear fusion reactors are composed of several complex components whose behavior may be not certain a priori. This uncertainty may have a significant impact on the evolution of fault transients in the machine, causing unexpected damage to its components. For this reason, a suitable method for the uncertainty propagation during those transients is required. The Monte Carlo method would be the reference option, but it is, in most of the cases, not applicable due to the large number of required, repeated simulations. In this context, the Polynomial Chaos Expansion has been considered as a valuable alternative. It allows us to create a surrogate model of the original one in terms of orthogonal polynomials. Then, the uncertainty quantification is performed repeatedly, relying on this much simpler and faster model. Using the fast current discharge in the Divertor Tokamak Test Toroidal Field (DTT TF) coils as a reference scenario, the following method has been applied: the uncertainty on the parameters of the Fast Discharge Unit (FDU) varistor disks is propagated to the simulated electrical and electromagnetic relevant effects. Eventually, two worst-case scenarios are analyzed from a thermal–hydraulic point of view with the 4C code, simulating a fast current discharge as a consequence of a coil quench. It has been demonstrated that the uncertainty on the inputs (varistor parameters) strongly propagates, leading to a wide range of possible scenarios in the case of accidental transients. This result underlines the necessity of taking into account and propagating all possible uncertainties in the design of a fusion reactor according to the Best Estimate Plus Uncertainty approach. The uncertainty propagation from input data to electrical, electromagnetic, and thermal hydraulic results, using surrogate models, is the first of its kind in the field of the modeling of superconducting magnets for nuclear fusion applications
A genetic algorithm to optimize the multi-group structure for the neutronic analyses of the ARC fusion reactor
No full textIn the framework of the modeling of fusion reactors with deterministic neutronic codes, the choice of an appropriate energy grid for the generation of the multigroup nuclear properties is essential. In this work, a Genetic Algorithm is employed to optimize the energy grid employed in the nemoFoam multiphysics code to reproduce the results provided by the Monte Carlo code Serpent in terms of neutron flux, neutron power deposition and Tritium Breeding Ratio for the Affordable, Robust and Compact (ARC) fusion reactor. Different runs of the Genetic Algorithm are performed, with the aim of optimizing not only the quantities of interest separately, but also trying to combine them thanks to the definition of appropriate fitness functions. The optimization is performed starting from a pre-defined 86 groups energy grid, over which the nuclear properties and the reference quantities are evaluated with Serpent. The results show that it is not straightforward to optimize at the same time the energy grid for different quantities and that, in general, coarse energy grids are able to provide good results in nemoFoam for what concerns the ARC reactor, allowing to alleviate the computational burden of the neutronic evaluation too
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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