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- 저자 : Hollands T. (검색결과 4 건)
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OECD/NEA Sandia Fuel Project phase I: Benchmark of the ignition testing
Adorni, M.,Herranz, L.E.,Hollands, T.,Ahn, K.I.,Bals, C.,D'Auria, F.,Horvath, G.L.,Jaeckel, B.S.,Kim, H.C.,Lee, J.J.,Ogino, M.,Techy, Z.,Velazquez-Lozad, A.,Zigh, A.,Rehacek, R. North-Holland Pub. Co 2016 Nuclear engineering and design Vol.307 No.-
The OECD/NEA Sandia Fuel Project provided unique thermal-hydraulic experimental data associated with Spent Fuel Pool (SFP) complete drain down. The study conducted at Sandia National Laboratories (SNL) was successfully completed (July 2009 to February 2013). The accident conditions of interest for the SFP were simulated in a full scale prototypic fashion (electrically heated, prototypic assemblies in a prototypic SFP rack) so that the experimental results closely represent actual fuel assembly responses. A major impetus for this work was to facilitate severe accident code validation and to reduce modeling uncertainties within the codes. Phase I focused on axial heating and burn propagation in a single PWR 17x17 assembly (i.e. ''hot neighbors'' configuration). Phase II addressed axial and radial heating and zirconium fire propagation including effects of fuel rod ballooning in a 1x4 assembly configuration (i.e. single, hot center assembly and four, ''cooler neighbors''). This paper summarizes the comparative analysis regarding the final destructive ignition test of the phase I of the project. The objective of the benchmark is to evaluate and compare the predictive capabilities of computer codes concerning the ignition testing of PWR fuel assemblies. Nine institutions from eight different countries were involved in the benchmark calculations. The time to ignition and the maximum temperature are adequately captured by the calculations. It is believed that the benchmark constitutes an enlargement of the validation range for the codes to the conditions tested, thus enhancing the code applicability to other fuel assembly designs and configurations. The comparison of lumped parameter and CFD computer codes represents a further valuable achievement.
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Δ additive and Δ ultra-additive maps, Gromov's trees, and the Farris transform
Dress, A.,Holland, B.,Huber, K.T.,Koolen, J.H.,Moulton, V.,Weyer-Menkhoff, J. Elsevier 2005 Discrete Applied Mathematics Vol.146 No.1
<P><B>Abstract</B></P><P>In phylogenetic analysis, one searches for phylogenetic trees that reflect observed similarity between a collection of species in question. To this end, one often invokes two simple facts: (i) Any tree is completely determined by the metric it induces on its leaves (which represent the species). (ii) The resulting metrics are characterized by their property of being <I>additive</I> or, in the case of dated rooted trees, <I>ultra-additive</I>. Consequently, searching for additive or ultra-additive metrics <I>A</I> that best approximate the metric <I>D</I> encoding the observed similarities is a standard task in phylogenetic analysis. Remarkably, while there are efficient algorithms for constructing optimal ultra-additive approximations, the problem of finding optimal additive approximations in the <SUB>l1</SUB> or <SUB>l∞</SUB> sense is NP-hard. In the context of the theory of δ-<I>hyperbolic</I> groups, however, good additive approximations <I>A</I> of a metric <I>D</I> were found by Gromov already in 1988 and shown to satisfy the bound∥D-A<SUB>∥∞</SUB>⩽Δ(D)⌈<SUB>log2</SUB>(#X-1)⌉,where Δ(D), the <I>hyperbolicity</I> of <I>D</I>, i.e. the maximum of all expressions of the formD(u,v)+D(x,y)-max(D(u,x)+D(v,y),D(u,y)+D(v,x))(u,v,x,y∈X). Yet, besides some notable exceptions (e.g. Adv. Appl. Math. 27 (2001) 733–767), the potential of Gromov's concept of hyperbolicity is far from being fully explored within the context of phylogenetic analysis. In this paper, we provide the basis for a systematic theory of Δ <I>ultra-additive</I> and Δ <I>additive</I> approximations. In addition, we also explore the average and worst case behavior of Gromov's bound.</P>
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The TANDEM Euratom project: Context, objectives and workplan
Vaglio-Gaudard C.,Dominguez Bautista M.T.,Frignani M.,Fütterer M.,Goicea A.,Hanus E.,Hollands T.,Lombardo C.,Lorenzi S.,Miss J.,Pavel G.,Pucciarelli A.,Ricotti M.,Ruby A.,Schneidesch C.,Sholomitsky S. 한국원자력학회 2024 Nuclear Engineering and Technology Vol.56 No.3
The TANDEM project is a European initiative funded under the EURATOM program. The project started on September 2022 and has a duration of 36 months. TANDEM stands for Small Modular ReacTor for a European sAfe aNd Decarbonized Energy Mix. Small Modular Reactors (SMRs) can be hybridized with other energy sources, storage systems and energy conversion applications to provide electricity, heat and hydrogen. Hybrid energy systems have the potential to strongly contribute to the energy decarbonization targeting carbon-neutrality in Europe by 2050. However, the integration of nuclear reactors, particularly SMRs, in hybrid energy systems, is a new R&D topic to be investigated. In this context, the TANDEM project aims to develop assessments and tools to facilitate the safe and efficient integration of SMRs into low-carbon hybrid energy systems. An open-source “TANDEM” model library of hybrid system components will be developed in Modelica language which, by coupling, will extend the capabilities of existing tools implemented in the project. The project proposes to specifically address the safety issues of SMRs related to their integration into hybrid energy systems, involving specific interactions between SMRs and the rest of the hybrid systems; new initiating events may have to be considered in the safety approach. TANDEM will study two hybrid systems covering the main trends of the European energy policy and market evolution at 2035’s horizon: a district heating network and power supply in a large urban area, and an energy hub serving energy conversion systems, including hydrogen production; the energy hub is inspired from a harbor-like infrastructure. TANDEM will provide assessments on SMR safety, hybrid system operationality and techno-economics. Societal considerations will also be encased by analyzing European citizen engagement in SMR technology safety.
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