An aggregated wind power generation model based on MERRA reanalysis data: MATLAB model and example data for the April 2014 wind farm distribution of Great Britain.

The MATLAB model is contained within the compressed folders (versions are available as .zip and .tgz). This model uses MERRA reanalysis data (>34 years available) to estimate the hourly aggregated wind power generation for a predefined (fixed) distribution of wind farms. A ready made example is included for the wind farm distribution of Great Britain, April 2014 ("CF.dat"). This consists of an hourly time series of GB-total capacity factor spanning the period 1980-2013 inclusive. Given the global nature of reanalysis data, the model can be applied to any specified distribution of wind farms in any region of the world. Users are, however, strongly advised to bear in mind the limitations of reanalysis data when using this model/data. This is discussed in our paper: Cannon, Brayshaw, Methven, Coker, Lenaghan. "Using reanalysis data to quantify extreme wind power generation statistics: a 33 year case study in Great Britain". Submitted to Renewable Energy in March, 2014. Additional information about the model is contained in the model code itself, in the accompanying ReadMe file, and on our website: http://www.met.reading.ac.uk/~energymet/data/Cannon2014/

Algorithms for two-dimensional cutting stock and strip packing problems using dynamic programming and column generation

We investigate several two-dimensional guillotine cutting stock problems and their variants in which orthogonal rotations are allowed. We first present two dynamic programming based algorithms for the Rectangular Knapsack (RK) problem and its variants in which the patterns must be staged. The first algorithm solves the recurrence formula proposed by Beasley; the second algorithm - for staged patterns - also uses a recurrence formula. We show that if the items are not so small compared to the dimensions of the bin, then these algorithms require polynomial time. Using these algorithms we solved all instances of the RK problem found at the OR-LIBRARY, including one for which no optimal solution was known. We also consider the Two-dimensional Cutting Stock problem. We present a column generation based algorithm for this problem that uses the first algorithm above mentioned to generate the columns. We propose two strategies to tackle the residual instances. We also investigate a variant of this problem where the bins have different sizes. At last, we study the Two-dimensional Strip Packing problem. We also present a column generation based algorithm for this problem that uses the second algorithm above mentioned where staged patterns are imposed. In this case we solve instances for two-, three- and four-staged patterns. We report on some computational experiments with the various algorithms we propose in this paper. The results indicate that these algorithms seem to be suitable for solving real-world instances. We give a detailed description (a pseudo-code) of all the algorithms presented here, so that the reader may easily implement these algorithms. (c) 2007 Elsevier B.V. All rights reserved.

Integrating open source codes for solid modeling and automatic mesh generation in FEM applications

The applications of the Finite Element Method (FEM) for three-dimensional domains are already well documented in the framework of Computational Electromagnetics. However, despite the power and reliability of this technique for solving partial differential equations, there are only a few examples of open source codes available and dedicated to the solid modeling and automatic constrained tetrahedralization, which are the most time consuming steps in a typical three-dimensional FEM simulation. Besides, these open source codes are usually developed separately by distinct software teams, and even under conflicting specifications. In this paper, we describe an experiment of open source code integration for solid modeling and automatic mesh generation. The integration strategy and techniques are discussed, and examples and performance results are given, specially for complicated and irregular volumes which are not simply connected. © 2011 IEEE.

Three-dimensional modeling and highly refined mesh generation of the aorta artery and its tunics

This paper describes strategies and techniques to perform modeling and automatic mesh generation of the aorta artery and its tunics (adventitia, media and intima walls), using open source codes. The models were constructed in the Blender package and Python scripts were used to export the data necessary for the mesh generation in TetGen. The strategies proposed are able to provide meshes of complicated and irregular volumes, with a large number of mesh elements involved (12,000,000 tetrahedrons approximately). These meshes can be used to perform computational simulations by Finite Element Method (FEM). © Published under licence by IOP Publishing Ltd.

Proposal for a code of good practice in statistics in Latin America and the Caribbean and implementation plan for 2012-2013

Incluye Bibliografía

Abstraction-carrying code: a model for mobile code safety

Proof-Carrying Code (PCC) is a general approach to mobile code safety in which programs are augmented with a certificate (or proof). The intended benefit is that the program consumer can locally validate the certificate w.r.t. the "untrustcd" program by means of a certificate checker a process which should be much simpler, efficient, and automatic than generating the original proof. The practical uptake of PCC greatly depends on the existence of a variety of enabling technologies which allow both proving programs correct and replacing a costly verification process by an efficient checking proceduri on th( consumer side. In this work we propose Abstraction- Carrying Code (ACC), a novel approach which uses abstract interpretation as enabling technology. We argue that the large body of applications of abstract interpretation to program verification is amenable to the overall PCC scheme. In particular, we rely on an expressive class of safely policies which can be defined over different abstract domains. We use an abstraction (or abstract model) of the program computed by standard static analyzers as a certificate. The validity of the abstraction on ihe consumer side is checked in a single pass by a very efficient and specialized abstract-interpreter. We believe that ACC brings the expressiveness, flexibility and automation which is inherent in abstract interpretation techniques to the area of mobile code safety.

Steps Ahead in the Few-Group CRoss-Section Library Generation at the Pin Level

There exists an interest in performing pin-by-pin calculations coupled with thermal hydraulics so as to improve the accuracy of nuclear reactor analysis. In the framework of the EU NURISP project, INRNE and UPM have generated an experimental version of a few group diffusion cross sections library with discontinuity factors intended for VVER analysis at the pin level with the COBAYA3 code. The transport code APOLLO2 was used to perform the branching calculations. As a first proof of principle the library was created for fresh fuel and covers almost the full parameter space of steady state and transient conditions. The main objective is to test the calculation schemes and post-processing procedures, including multi-pin branching calculations. Two library options are being studied: one based on linear table interpolation and another one using a functional fitting of the cross sections. The libraries generated with APOLLO2 have been tested with the pin-by-pin diffusion model in COBAYA3 including discontinuity factors; first comparing 2D results against the APOLLO2 reference solutions and afterwards using the libraries to compute a 3D assembly problem coupled with a simplified thermal-hydraulic model.

Reduced certificates for abstraction-carrying code

Abstraction-Carrying Code (ACC) has recently been proposed as a framework for mobile code safety in which the code supplier provides a program together with an abstraction whose validity entails compliance with a predefined safety policy. The abstraction plays thus the role of safety certifícate and its generation is carried out automatically by a fixed-point analyzer. The advantage of providing a (fixedpoint) abstraction to the code consumer is that its validity is checked in a single pass of an abstract interpretation-based checker. A main challenge is to reduce the size of certificates as much as possible while at the same time not increasing checking time. We introduce the notion of reduced certifícate which characterizes the subset of the abstraction which a checker needs in order to validate (and re-construct) the full certifícate in a single pass. Based on this notion, we instrument a generic analysis algorithm with the necessary extensions in order to identify the information relevant to the checker. We also provide a correct checking algorithm together with sufficient conditions for ensuring its completeness. The experimental results within the CiaoPP system show that our proposal is able to greatly reduce the size of certificates in practice.

Abstraction-carrying code

Proof-Carrying Code (PCC) is a general approach to mobile code safety in which programs are augmented with a certifícate (or proof). The practical uptake of PCC greatly depends on the existence of a variety of enabling technologies which allow both to prove programs correct and to replace a costly verification process by an efñcient checking procedure on the consumer side. In this work we propose Abstraction-Carrying Code (ACC), a novel approach which uses abstract interpretation as enabling technology. We argüe that the large body of applications of abstract interpretation to program verification is amenable to the overall PCC scheme. In particular, we rely on an expressive class of safety policies which can be defined over different abstract domains. We use an abstraction (or abstract model) of the program computed by standard static analyzers as a certifícate. The validity of the abstraction on the consumer side is checked in a single-pass by a very efficient and specialized abstract-interpreter. We believe that ACC brings the expressiveness, flexibility and automation which is inherent in abstract interpretation techniques to the área of mobile code safety. We have implemented and benchmarked ACC within the Ciao system preprocessor. The experimental results show that the checking phase is indeed faster than the proof generation phase, and that the sizes of certificates are reasonable.

On abstraction-carrying code and certificate-size reduction

Abstraction-Carrying Code (ACC) is a framework for mobile code safety in which the code supplier provides a program together with an abstraction (or abstract model of the program) whose validity entails compliance with a predefined safety policy. The abstraction plays thus the role of safety certificate and its generation is carried out automatically by a fixed-point analyzer. The advantage of providing a (fixed-point) abstraction to the code consumer is that its validity is checked in a single pass (i.e., one iteration) of an abstract interpretation-based checker. A main challenge to make ACC useful in practice is to reduce the size of certificates as much as possible, while at the same time not increasing checking time. Intuitively, we only include in the certificate the information which the checker is unable to reproduce without iterating. We introduce the notion of reduced certifícate which characterizes the subset of the abstraction which a checker needs in order to validate (and re-construct) the full certificate in a single pass. Based on this notion, we show how to instrument a generic analysis algorithm with the necessary extensions in order to identify the information relevant to the checker.

Abstraction carrying code and resource-awareness

Proof-Carrying Code (PCC) is a general approach to mobile code safety in which the code supplier augments the program with a certifícate (or proof). The intended benefit is that the program consumer can locally validate the certifícate w.r.t. the "untrusted" program by means of a certifícate checker—a process which should be much simpler, eíñcient, and automatic than generating the original proof. Abstraction Carrying Code (ACC) is an enabling technology for PCC in which an abstract model of the program plays the role of certifícate. The generation of the certifícate, Le., the abstraction, is automatically carried out by an abstract interpretation-based analysis engine, which is parametric w.r.t. different abstract domains. While the analyzer on the producer side typically has to compute a semantic fixpoint in a complex, iterative process, on the receiver it is only necessary to check that the certifícate is indeed a fixpoint of the abstract semantics equations representing the program. This is done in a single pass in a much more efficient process. ACC addresses the fundamental issues in PCC and opens the door to the applicability of the large body of frameworks and domains based on abstract interpretation as enabling technology for PCC. We present an overview of ACC and we describe in a tutorial fashion an application to the problem of resource-aware security in mobile code. Essentially the information computed by a cost analyzer is used to genérate cost certificates which attest a safe and efficient use of a mobile code. A receiving side can then reject code which brings cost certificates (which it cannot validate or) which have too large cost requirements in terms of computing resources (in time and/or space) and accept mobile code which meets the established requirements.

Reduced certificates for abstraction-carrying code

Abstraction-Carrying Code (ACC) has recently been proposed as a framework for mobile code safety in which the code supplier provides a program together with an abstraction (or abstract model of the program) whose validity entails compliance with a predefined safety policy. The abstraction plays thus the role of safety certifícate and its generation is carried out automatically by a fixed-point analyzer. The advantage of providing a (fixed-point) abstraction to the code consumer is that its validity is checked in a single pass (i.e., one iteration) of an abstract interpretation-based checker. A main challenge to make ACC useful in practice is to reduce the size of certificates as much as possible while at the same time not increasing checking time. The intuitive idea is to only include in the certifícate information that the checker is unable to reproduce without iterating. We introduce the notion of reduced certifícate which characterizes the subset of the abstraction which a checker needs in order to validate (and re-construct) the full certifícate in a single pass. Based on this notion, we instrument a generic analysis algorithm with the necessary extensions in order to identify information which can be reconstructed by the single-pass checker. Finally, we study what the effects of reduced certificates are on the correctness and completeness of the checking process. We provide a correct checking algorithm together with sufficient conditions for ensuring its completeness. Our ideas are illustrated through a running example, implemented in the context of constraint logic programs, which shows that our approach improves state-of-the-art techniques for reducing the size of certificates.

Certificate size reduction in abstraction-carrying code

Abstraction-Carrying Code (ACC) has recently been proposed as a framework for mobile code safety in which the code supplier provides a program together with an abstraction (or abstract model of the program) whose validity entails compliance with a predefined safety policy. The abstraction plays thus the role of safety certificate and its generation is carried out automatically by a fixpoint analyzer. The advantage of providing a (fixpoint) abstraction to the code consumer is that its validity is checked in a single pass (i.e., one iteration) of an abstract interpretation-based checker. A main challenge to make ACC useful in practice is to reduce the size of certificates as much as possible while at the same time not increasing checking time. The intuitive idea is to only include in the certificate information that the checker is unable to reproduce without iterating. We introduce the notion of reduced certificate which characterizes the subset of the abstraction which a checker needs in order to validate (and re-construct) the fall certificate in a single pass. Based on this notion, we instrument a generic analysis algorithm with the necessary extensions in order to identify the information relevant to the checker. Interestingly, the fact that the reduced certificate omits (parts of) the abstraction has implications in the design of the checker. We provide the sufficient conditions which allow us to ensure that 1) if the checker succeeds in validating the certificate, then the certificate is valid for the program (correctness) and 2) the checker will succeed for any reduced certificate which is valid (completeness). Our approach has been implemented and benchmarked within the CiaoPP system. The experimental results show t h a t our proposal is able to greatly reduce the size of certificates in practice. To appear in Theory and Practice of Logic Programming (TPLP).

Analysis of a Spanish energy scenario with Generation IV nuclear reactors

The advantages of fast-spectrum reactors consist not only of an efficient use of fuel through the breeding of fissile material and the use of natural or depleted uranium, but also of the potential reduction of the amount of actinides such as americium and neptunium contained in the irradiated fuel. The first aspect means a guaranteed future nuclear fuel supply. The second fact is key for high-level radioactive waste management, because these elements are the main responsible for the radioactivity of the irradiated fuel in the long term. The present study aims to analyze the hypothetical deployment of a Gen-IV Sodium Fast Reactor (SFR) fleet in Spain. A nuclear fleet of fast reactors would enable a fuel cycle strategy different than the open cycle, currently adopted by most of the countries with nuclear power. A transition from the current Gen-II to Gen-IV fleet is envisaged through an intermediate deployment of Gen-III reactors. Fuel reprocessing from the Gen-II and Gen-III Light Water Reactors (LWR) has been considered. In the so-called advanced fuel cycle, the reprocessed fuel used to produce energy will breed new fissile fuel and transmute minor actinides at the same time. A reference case scenario has been postulated and further sensitivity studies have been performed to analyze the impact of the different parameters on the required reactor fleet. The potential capability of Spain to supply the required fleet for the reference scenario using national resources has been verified. Finally, some consequences on irradiated final fuel inventory are assessed. Calculations are performed with the Monte Carlo transport-coupled depletion code SERPENT together with post-processing tools.

Core physics and safety analysis of Generation-IV Sodium Fast Reactors using existing and newly developed computational tools

El futuro de la energía nuclear de fisión dependerá, entre otros factores, de la capacidad que las nuevas tecnologías demuestren para solventar los principales retos a largo plazo que se plantean. Los principales retos se pueden resumir en los siguientes aspectos: la capacidad de proporcionar una solución final, segura y fiable a los residuos radiactivos; así como dar solución a la limitación de recursos naturales necesarios para alimentar los reactores nucleares; y por último, una mejora robusta en la seguridad de las centrales que en definitiva evite cualquier daño potencial tanto en la población como en el medio ambiente como consecuencia de cualquier escenario imaginable o más allá de lo imaginable. Siguiendo estas motivaciones, la Generación IV de reactores nucleares surge con el compromiso de proporcionar electricidad de forma sostenible, segura, económica y evitando la proliferación de material fisible. Entre los sistemas conceptuales que se consideran para la Gen IV, los reactores rápidos destacan por su capacidad potencial de transmutar actínidos a la vez que permiten una utilización óptima de los recursos naturales. Entre los refrigerantes que se plantean, el sodio parece una de las soluciones más prometedoras. Como consecuencia, esta tesis surgió dentro del marco del proyecto europeo CP-ESFR con el principal objetivo de evaluar la física de núcleo y seguridad de los reactores rápidos refrigerados por sodio, al tiempo que se desarrollaron herramientas apropiadas para dichos análisis. Efectivamente, en una primera parte de la tesis, se abarca el estudio de la física del núcleo de un reactor rápido representativo, incluyendo el análisis detallado de la capacidad de transmutar actínidos minoritarios. Como resultado de dichos análisis, se publicó un artículo en la revista Annals of Nuclear Energy [96]. Por otra parte, a través de un análisis de un hipotético escenario nuclear español, se evalúo la disponibilidad de recursos naturales necesarios en el caso particular de España para alimentar una flota específica de reactores rápidos, siguiendo varios escenarios de demanda, y teniendo en cuenta la capacidad de reproducción de plutonio que tienen estos sistemas. Como resultado de este trabajo también surgió una publicación en otra revista científica de prestigio internacional como es Energy Conversion and Management [97]. Con objeto de realizar esos y otros análisis, se desarrollaron diversos modelos del núcleo del ESFR siguiendo varias configuraciones, y para diferentes códigos. Por otro lado, con objeto de poder realizar análisis de seguridad de reactores rápidos, son necesarias herramientas multidimensionales de alta fidelidad específicas para reactores rápidos. Dichas herramientas deben integrar fenómenos relacionados con la neutrónica y con la termo-hidráulica, entre otros, mediante una aproximación multi-física. Siguiendo este objetivo, se evalúo el código de difusión neutrónica ANDES para su aplicación a reactores rápidos. ANDES es un código de resolución nodal que se encuentra implementado dentro del sistema COBAYA3 y está basado en el método ACMFD. Por lo tanto, el método ACMFD fue sometido a una revisión en profundidad para evaluar su aptitud para la aplicación a reactores rápidos. Durante ese proceso, se identificaron determinadas limitaciones que se discutirán a lo largo de este trabajo, junto con los desarrollos que se han elaborado e implementado para la resolución de dichas dificultades. Por otra parte, se desarrolló satisfactoriamente el acomplamiento del código neutrónico ANDES con un código termo-hidráulico de subcanales llamado SUBCHANFLOW, desarrollado recientemente en el KIT. Como conclusión de esta parte, todos los desarrollos implementados son evaluados y verificados. En paralelo con esos desarrollos, se calcularon para el núcleo del ESFR las secciones eficaces en multigrupos homogeneizadas a nivel nodal, así como otros parámetros neutrónicos, mediante los códigos ERANOS, primero, y SERPENT, después. Dichos parámetros se utilizaron más adelante para realizar cálculos estacionarios con ANDES. Además, como consecuencia de la contribución de la UPM al paquete de seguridad del proyecto CP-ESFR, se calcularon mediante el código SERPENT los parámetros de cinética puntual que se necesitan introducir en los típicos códigos termo-hidráulicos de planta, para estudios de seguridad. En concreto, dichos parámetros sirvieron para el análisis del impacto que tienen los actínidos minoritarios en el comportamiento de transitorios. Concluyendo, la tesis presenta una aproximación sistemática y multidisciplinar aplicada al análisis de seguridad y comportamiento neutrónico de los reactores rápidos de sodio de la Gen-IV, usando herramientas de cálculo existentes y recién desarrolladas ad' hoc para tal aplicación. Se ha empleado una cantidad importante de tiempo en identificar limitaciones de los métodos nodales analíticos en su aplicación en multigrupos a reactores rápidos, y se proponen interesantes soluciones para abordarlas. ABSTRACT The future of nuclear reactors will depend, among other aspects, on the capability to solve the long-term challenges linked to this technology. These are the capability to provide a definite, safe and reliable solution to the nuclear wastes; the limitation of natural resources, needed to fuel the reactors; and last but not least, the improved safety, which would avoid any potential damage on the public and or environment as a consequence of any imaginable and beyond imaginable circumstance. Following these motivations, the IV Generation of nuclear reactors arises, with the aim to provide sustainable, safe, economic and proliferationresistant electricity. Among the systems considered for the Gen IV, fast reactors have a representative role thanks to their potential capacity to transmute actinides together with the optimal usage of natural resources, being the sodium fast reactors the most promising concept. As a consequence, this thesis was born in the framework of the CP-ESFR project with the generic aim of evaluating the core physics and safety of sodium fast reactors, as well as the development of the approppriated tools to perform such analyses. Indeed, in a first part of this thesis work, the main core physics of the representative sodium fast reactor are assessed, including a detailed analysis of the capability to transmute minor actinides. A part of the results obtained have been published in Annals of Nuclear Energy [96]. Moreover, by means of the analysis of a hypothetical Spanish nuclear scenario, the availability of natural resources required to deploy an specific fleet of fast reactor is assessed, taking into account the breeding properties of such systems. This work also led to a publication in Energy Conversion and Management [97]. In order to perform those and other analyses, several models of the ESFR core were created for different codes. On the other hand, in order to perform safety studies of sodium fast reactors, high fidelity multidimensional analysis tools for sodium fast reactors are required. Such tools should integrate neutronic and thermal-hydraulic phenomena in a multi-physics approach. Following this motivation, the neutron diffusion code ANDES is assessed for sodium fast reactor applications. ANDES is the nodal solver implemented inside the multigroup pin-by-pin diffusion COBAYA3 code, and is based on the analytical method ACMFD. Thus, the ACMFD was verified for SFR applications and while doing so, some limitations were encountered, which are discussed through this work. In order to solve those, some new developments are proposed and implemented in ANDES. Moreover, the code was satisfactorily coupled with the thermal-hydraulic code SUBCHANFLOW, recently developed at KIT. Finally, the different implementations are verified. In addition to those developments, the node homogenized multigroup cross sections and other neutron parameters were obtained for the ESFR core using ERANOS and SERPENT codes, and employed afterwards by ANDES to perform steady state calculations. Moreover, as a result of the UPM contribution to the safety package of the CP-ESFR project, the point kinetic parameters required by the typical plant thermal-hydraulic codes were computed for the ESFR core using SERPENT, which final aim was the assessment of the impact of minor actinides in transient behaviour. All in all, the thesis provides a systematic and multi-purpose approach applied to the assessment of safety and performance parameters of Generation-IV SFR, using existing and newly developed analytical tools. An important amount of time was employed in identifying the limitations that the analytical nodal diffusion methods present when applied to fast reactors following a multigroup approach, and interesting solutions are proposed in order to overcome them.