Two-point theory for the differential self-interrogation Feynman-alpha method

A Feynman-alpha formula has been derived in a two region domain pertaining the stochastic differential self-interrogation (DDSI) method and the differential die-away method (DDAA). Monte Carlo simulations have been used to assess the applicability of the variance to mean through determination of the physical reaction intensities of the physical processes in the two domains. More specifically, the branching processes of the neutrons in the two regions are described by the Chapman - Kolmogorov equation, including all reaction intensities for the various processes, that is used to derive a variance to mean relation for the process. The applicability of the Feynman-alpha or variance to mean formulae are assessed in DDSI and DDAA of spent fuel configurations.Comment: 15 pages, 5 figures. Submitted to EPJ Plu

Rough Sets: a Bibliometric Analysis from 2014 to 2018

Along almost forty years, considerable research has been undertaken on rough set theory to deal with vague information. Rough sets have proven to be extremely helpful for a diversity of computer-science problems (e.g., knowledge discovery, computational logic, machine learning, etc.), and numerous application domains (e.g., business economics, telecommunications, neurosciences, etc.). Accordingly, the literature on rough sets has grown without ceasing, and nowadays it is immense. This paper provides a comprehensive overview of the research published for the last five years. To do so, it analyzes 4,038 records retrieved from the Clarivate Web of Science database, identifying (i) the most prolific authors and their collaboration networks, (ii) the countries and organizations that are leading research on rough sets, (iii) the journals that are publishing most papers, (iv) the topics that are being most researched, and (v) the principal application domains

Experimental Measurements and CFD Results of Liquid Film Thickness in Vertical Downward Air-Water Annular Flow

[EN] Annular gas¿liquid flows have been extensively studied over the years. However, the nonlinear behavior of the interface is still currently the subject of study by multiple researchers worldwide. The appearance of a liquid layer on the wall and its turbulent behavior support the heat exchange of multiple systems in the industrial field. Research in this area allows the optimization of these installations as well as the analysis of possible safety problems if the liquid film disappears. This study first shows some of the most important findings obtained in the GEPELON experimental facility (GEneración de PElícula ONdulatoria or Wavy Film Generator). The facility was built in order to analyze the behavior of the liquid film in annular downward air¿water flow. The experimental range of the inlet conditions is 800¿8000 for the ReL and 0¿110,000 for the Reg. Measurements for the mean film thickness show a fairly good agreement with the empirical correlations and the measurements of other authors. One of the most demanded applications of this type of measurements is the validation of computational dynamics or CFD codes. Therefore, the experiment has been modeled using Ansys CFX software, and the simulation results have been compared with the experimental ones. This article outlines some of the reasons why two-phase flow simulations are currently challenging and how the codes are able to overcome them. Simulation predictions are fairly close to the experimental measurements, and the mean film thickness evolution when changing the boundary conditions also shows a good agreement.The authors are indebted to the plan of I+D support of the EXMOTRANSIN project ENE2016-79489-C2-1-P.Rivera-Durán, Y.; J. L. Muñoz-Cobo; A. Escrivá; C. Berna; Y. Córdova (2022). Experimental Measurements and CFD Results of Liquid Film Thickness in Vertical Downward Air-Water Annular Flow. International Journal of Computational Methods and Experimental Measurements. 10(2):93-103. https://doi.org/10.2495/CMEM-V10-N2-93-1039310310

Experiments in free falling and downward cocurrent annular flows-Characterization of liquid films and interfacial waves

[EN] Falling liquid films and downward cocurrent flows in rounded shape pipes have been experimentally studied during the last decades, estimating the evolution of its major characteristics. The most important variables during the formation and growth of surface waves in falling downward flows have been measured using conductance probes. The main objective of the current research paper is to study the dependency of the characteristics of the thin liquid layer for downward cocurrent annular flows. The GEPELON experimental facility consists of a vertical pipe with 3.8 m of useful test length. Two pipe diameters have been analysed in this experimental study, 42 and 30 mm, in which the range covered by the liquid Reynolds number varies between 570 and 8500 and 800-7900 respectively, while the gas Reynolds numbers vary from 0 to 7.9.10(4) and from 0 to 1.1.10(5) respectively for the mentioned pipe diameters. Up to five conductance probes have been placed along the pipes test sections to capture the liquid film thickness fluctuations along time at different distances of the pipe entrance for both developing and fully developed regions. After the study and analysis of the experimental data, the central point of this paper has been the development of new correlations for the liquid film thicknesses and the two major properties of the interfacial waves. Their adjustment procedure has been carried out in terms of dimensionless numbers, aiming to provide more general relationships. In particular, the magnitudes that characterise the interface behavior have been measured, particularly film thicknesses, average disturbance wave amplitudes, and disturbance wave frequencies for each boundary condition. An additional part of the document contains an extensive comparison between the results obtained in this study and the data and expressions of other authors. It has been confirmed the significant dispersion existing among different researchers, especially when analysing variables related to the interfacial waves. This highlights the lack of knowledge in some aspects even today. The different correlations proposed have been calculated based on the best fit of the data from all the series of experiments carried out in this study. Comparisons of the behaviour of these correlations with data from other researchers have also been included.This research is supported by the EXMOTRANSIN project ENE2016-79489-C2-1-P included in the I + D Spanish plan. Funding for open access charge: CRUE-Universitat Politècnica de València.Rivera-Durán, Y.; Berna, C.; Muñoz-Cobo, JL.; Escrivá, A.; Córdova, Y. (2022). Experiments in free falling and downward cocurrent annular flows-Characterization of liquid films and interfacial waves. Nuclear Engineering and Design. 392:1-23. https://doi.org/10.1016/j.nucengdes.2022.11176912339

APPLICATION OF THE STOCHASTIC TRANSPORT THEORY TO REACTIVITY MEASUREMENTS IN A SUBCRITICAL ASSEMBLY DRIVEN BY A PULSED SOURCE

ABSTRACT Using the stochastic transport theory formalism developed by Muñoz-Cobo for a radioactive source and for a spallation source, we derive an expression for the Cross Power Spectral Density (CPSD) for a subcritical system driven by an external pulsed neutron source. The derivation of this expression has been done in a rigorous and general way including the energy and spatial dependency. The CPSD shows some peaks at the source frequency together with its harmonics. The final expression containing some approximations (fundamental mode analysis; Dirac delta pulses for the source) is compared with calculations using a Monte Carlo code. In the future, comparisons with measurements in the MUSE project are planned

Obtención de las soluciones periódicas de un oscilador no lineal mediante un método rápido de Galerkin

Este artículo está enfocado a la determinación de las soluciones periódicas de los osciladores no lineales así como al análisis cualitativo de su estabilidad. Estos osciladores están modelizados por la ecuación diferencial 3 Z ( t ) + kk(t) + E ajzj = g(t) j=1 siendo g(t) una fuerza T-periódica. En este trabajo desarrollamos un algoritmo basado en el método de Galerkin que utiliza la transformada rápida de Fourier (FFT) para calcular las soluciones periódicas de la ecuación anterior. Además, incluimos un algoritmo combinado en un apéndice, con convergencia rápida, para resolver las ecuaciones algebraicas no lineales obtenidas por dicho método. Finalmente, validamos esta metodología aplicando el algoritmo pa,ra obtener las soluciones periódicas de un oscilador de Duffing con comportamiento caótico.This paper is focused to the determination of the harmonic solutions of the non linear oscillators modelled by the following differential equation 3 Z (t) + kk (t) + E a, r' = g (t) j=l being g(t) a T-periodic driving force. In this work we develop an algorithm based on the Galerkin method, using the Fast Fourier Transform (FFT) to calculate the harmonic solutions of previous equation. Furthermore, we include a combined algorithm with fast convergence to solve the non linear algebraic equations obtained in the Galerkin Fast Algorithm. Finally, we validate this methodology applying the algorithm to obtain the harmonic solutions of a Duffing oscillator with a chaotic behavior.Peer Reviewe

Development of Conductivity Sensors for Multi-Phase Flow Local Measurements at the Polytechnic University of Valencia (UPV) and University Jaume I of Castellon (UJI)

[EN] This paper describes all the procedures and methods currently used at UPV (Universitat Politécnica de Valencia) and UJI (University Jaume I) for the development and use of sensors for multi-phase flow analysis in vertical pipes. This paper also describes the methods that we use to obtain the values of the two-phase flow magnitudes from the sensor signals and the validation and cross-verification methods developed to check the consistency of the results obtained for these magnitudes with the sensors. First, we provide information about the procedures used to build the multi-sensor conductivity probes and some of the tests performed with different materials to avoid sensor degradation issues. In addition, we provide information about the characteristics of the electric circuits that feed the sensors. Then the data acquisition of the conductivity probe, the signal conditioning and the data processing including the device that have been designed to automatize all the measurement process of moving the sensors inside the channels by means of stepper electric motors controlled by computer are shown in operation. Then, we explain the methods used for bubble identification and categorization. Finally, we describe the methodology used to obtain the two-phase flow information from the sensor signals. This includes the following items: void fraction, gas velocity, Sauter mean diameter and interfacial area concentration. The last part of this paper is devoted to the conductance probes developed for the annular flow analysis, which includes the analysis of the interfacial waves produced in annular flow and that requires a different type of sensorThe authors are indebted to the support received from MINECO for the project MODEXFLAT ENE2013-48565-C2-1-P and ENE2013-48565-C2-2-P.Muñoz-Cobo, JL.; Chiva, S.; Mendez, S.; Monrós, G.; Escrivá, A.; Cuadros-Orón, JL. (2017). Development of Conductivity Sensors for Multi-Phase Flow Local Measurements at the Polytechnic University of Valencia (UPV) and University Jaume I of Castellon (UJI). Sensors. 17(5):1-35. https://doi.org/10.3390/s17051077S13517

Methodology and Application of Statistical Techniques to Evaluate the Reliability of Electrical Systems Based on the Use of High Variability Generation Sources

[EN] This study presents a new methodology, based on Monte-Carlo techniques to evaluate the reliability of a carbon-free electricity generation system based on renewable sources; it uses as inputs the variation of the electricity demand and the fluctuations in the renewable supply and provides the renewable system to be installed to guarantee a specific supply reliability level. Additionally, looking for a reduction of this renewable system, the methodology determines the improvements by the incorporation of nuclear power and electricity storage. The methodology is of general application, its implementation being possible under different contexts, such as different time horizons and different future energy scenarios, both for developing, emerging, and developed countries. The only requirement is to have a sufficient database from which to make predictions for future scenarios of electrical generation-demand balances. As an example of practical implementation, the electrical system reliability for the particular case of Spain in 2040 has been forecasted. When considering the fluctuations in solar and wind power contributions, very high values of the installed power from these renewable sources are needed to reach a high reliability of the system. These values decrease substantially if contributions from nuclear and storage technologies are included.Berna-Escriche, C.; Pérez-Navarro, Á.; Escrivá, A.; Hurtado-Perez, E.; Muñoz-Cobo, JL.; Moros, MC. (2021). Methodology and Application of Statistical Techniques to Evaluate the Reliability of Electrical Systems Based on the Use of High Variability Generation Sources. Sustainability. 13(18):1-26. https://doi.org/10.3390/su131810098S126131

On the One-Dimensional Modeling of Vertical Upward Bubbly Flow

[EN] The one-dimensional two-fluid model approach has been traditionally used in thermal-hydraulics codes for the analysis of transients and accidents in water¿cooled nuclear power plants. This paper investigates the performance of RELAP5/MOD3 predicting vertical upward bubbly flow at low velocity conditions. For bubbly flow and vertical pipes, this code applies the drift- velocity approach, showing important discrepancies with the experiments compared. Then, we use a classical formulation of the drag coefficient approach to evaluate the performance of both approaches. This is based on the critical Weber criteria and includes several assumptions for the calculation of the interfacial area and bubble size that are evaluated in this work. A more accurate drag coefficient approach is proposed and implemented in RELAP5/MOD3. Instead of using the Weber criteria, the bubble size distribution is directly considered. This allows the calculation of the interfacial area directly from the definition of Sauter mean diameter of a distribution. The results show that only the proposed approach was able to predict all the flow characteristics, in particular the bubble size and interfacial area concentration. Finally, the computational results are analyzed and validated with cross-section area average measurements of void fraction, dispersed phase velocity, bubble size, and interfacial area concentration.The authors sincerely thank the Plan Nacional de I+D+i for funding the Projects MODEXFLAT ENE2013-48565-C2-1- P, ENE2013-48565-C2-2-P, and NUC-MULTPHYS ENE2012- 34585.Peña-Monferrer, C.; Gómez-Zarzuela, C.; Chiva, S.; Miró Herrero, R.; Verdú Martín, GJ.; Muñoz-Cobo, JL. (2018). On the One-Dimensional Modeling of Vertical Upward Bubbly Flow. Science and Technology of Nuclear Installations. 2018:1-10. https://doi.org/10.1155/2018/2153019S110201

Expansión en Caos Polinómico como método de Cuantificación de la Incertidumbre en simulaciones CFD. Aplicación al benchmark Cold-Leg Mixing de la OECD/NE

[ES] En este documento se presenta un estudio de la metodología de cuantificación de la incertidumbre mediante Expansión en Caos Polinómico (PCE por sus siglas en inglés). La teoría presentada es aplicada a un benchmark de la OECD/NEA denominado Cold-Leg Mixing. Este benchmark está basado en la instalación experimental que recibe el mismo nombre y está desarrollada por la Texas A&M University. Se muestran varios estudios de sensibilidad para optimizar el cálculo de la simulación. El modelo de turbulencia utilizado finalmente corresponde a un modelo tipo Large Eddy Simulation. Los resultados de la simulación muestran una buena concordancia con las medidas experimentales, en especial después de aplicar el PCE.Los autores de este trabajo desean destacar la contribución del plan de apoyo I+D del proyecto EXMOTRANSIN ENE2016-79489-C2-1-P.Rivera-Durán, Y.; Muñoz-Cobo, JL.; Berna, C.; Escrivá, A. (2019). Expansión en Caos Polinómico como método de Cuantificación de la Incertidumbre en simulaciones CFD. Aplicación al benchmark Cold-Leg Mixing de la OECD/NE. Sociedad Nuclear Española. 1-8. http://hdl.handle.net/10251/180968S1