<p>In order to monitor a nuclear boiling water reactor fixed and movable detectors are used, such as the neutron sensitive LPRM (Local Power Range Monitors) detectors and the gamma sensitive TIP (Traversing Incore Probe) detectors. These provide a mean to verify the predictions obtained from core simulators, which are used for planning and following up the reactor operation. The core simulators calculate e.g. the neutron flux and power distribution in the reactor core. The simulators can also simulate the response in the LPRM and TIP detectors. By comparing with measurements the accuracy of the core simulators can be quantified. The core simulators used in this work are PHOENIX4 and POLCA7. Because of the complexity of the calculations, each fuel assembly is divided axially into typically 25 nodes, which are more or less cubic with a side length of about 15 cm. Each axial segment is simulated using a 2D core simulator, in this work PHOENIX4, which provides data to the 3D code, in this case POLCA7, which in turn perform calculations for the whole core. The core simulators currently use both radial pin weights and axial node weights to calculate the gamma TIP detector signal. A need to bring forward new weight factors has now been identified because of the introduction of new fuel designs. Therefore, the gamma TIP detector response has been simulated using a Monte Carlo code called MCNPX for a modern fuel type, SVEA-96 Optima2, which is manufactured by Westinghouse. The new weights showed some significant differences compared to the old weights, which seem to overestimate the radial weight of the closest fuel pins and the axial weight of the node in front of the detector. The new weights were also implemented and tested in the core simulators, but no significant differences could be seen when comparing the simulated detector response using new and old weights to authentic TIP measurements.</p>

In order to monitor a nuclear boiling water reactor fixed and movable detectors are used, such as the neutron sensitive LPRM (Local Power Range Monitors) detectors and the gamma sensitive TIP (Traversing Incore Probe) detectors. These provide a mean to verify the predictions obtained from core simulators, which are used for planning and following up the reactor operation. The core simulators calculate e.g. the neutron flux and power distribution in the reactor core. The simulators can also simulate the response in the LPRM and TIP detectors. By comparing with measurements the accuracy of the core simulators can be quantified. The core simulators used in this work are PHOENIX4 and POLCA7. Because of the complexity of the calculations, each fuel assembly is divided axially into typically 25 nodes, which are more or less cubic with a side length of about 15 cm. Each axial segment is simulated using a 2D core simulator, in this work PHOENIX4, which provides data to the 3D code, in this case POLCA7, which in turn perform calculations for the whole core. The core simulators currently use both radial pin weights and axial node weights to calculate the gamma TIP detector signal. A need to bring forward new weight factors has now been identified because of the introduction of new fuel designs. Therefore, the gamma TIP detector response has been simulated using a Monte Carlo code called MCNPX for a modern fuel type, SVEA-96 Optima2, which is manufactured by Westinghouse. The new weights showed some significant differences compared to the old weights, which seem to overestimate the radial weight of the closest fuel pins and the axial weight of the node in front of the detector. The new weights were also implemented and tested in the core simulators, but no significant differences could be seen when comparing the simulated detector response using new and old weights to authentic TIP measurements.

This report investigates the steps of a one-way coupling between two simulation codes developed by Wesinghouse Electric Sweden AB. The Westinghouse POLCA8 is a three dimensional steady-state diffusion theory code used for simulating the neutronic, thermal and hydraulic behavior of a reactor core. In the  thermal-hydraulic module of the code, each fuel assembly is simulated as a one-dimensional channel, accounting for axial variations of the fuel geometry. While sufficient for many applications, the one-dimensional thermal-hydraulic approach may lack spatial resolution in the case of tilted radial power, very inhomogeneous fuel lattices or for specific calculations such as CHF (Critical Heat Flux) in PWR [3]. This limitation will b avoided by performing a code coupling with the sub-channel analysis code, VIPRE-W, to obtain the radial distribution of thermal-hydraulic parameters for each fuel assembly. In this thesis the codes are one-way coupled . To be able to do a coupling an interface is needed, and this has been created in Matlab. In the interface, the output from POLCA8 is converted into a form suitable to use as an input to VIPRE-W.  As an important first step in the coupling process, I have first analyzed how consistent the codes are when simulating the simplest thermal conditions inside the core. To be able to do the comparison,all values extracted from the sub-channel analysis code VIPRE-W must be converted into assembly-average-values, this is also done in the interface. The thermal-hydraulic parameters that have been  analyzed and compared in the two codes are; mass flux, quality and void.

Made available in DSpace on 2016-06-02T19:52:03Z (GMT). No. of bitstreams: 1 5876.pdf: 7013934 bytes, checksum: 4e3ff62ae5a65cf8026d92111fa732ee (MD5) Previous issue date: 2014-02-25 / In the latest decades, companies have faced important and increasing challenges set by globalization in product markets and production factors. This way, consumers become highly demanding and are always searching for new products, highly qualified, customized and quickly produced. Given these changes, the speed of delivery and therefore the efforts to reduce lead time emerges as one of the main objectives adopted by a company to compete in the market, since the strategies based in time aim to provide faster answers to its customers. In this context, the present paper aims to describe a proposal to reduce the lead time from the application of the concepts and methodology tools Quick Response Manufacturing (QRM) in a capital good sector s company. In order to achieve the proposed objective, a literature review about the QRM methodology and POLCA system and a case study in a company that develops and manufactures machinery and custom made equipment. Thus, it was analyzed the main causes of the waiting in the manufacturing of pressure vessels process, and through improvement proposals, it was achieved the results and gains expected. The main results, other than the 40% reduction in lead time, are related to quality improvement, increase of process responsibility in the manufacturing and simplifying the production control. / Nas últimas décadas as empresas têm enfrentado importantes e crescentes desafios impostos pela globalização dos mercados de produtos e fatores de produção. Dessa forma, os consumidores tornam-se cada vez mais exigentes e estão sempre em busca de novos produtos, altamente qualificados, customizados e produzidos rapidamente. Diante destas transformações, a velocidade de entrega e, por conseguinte, a busca pela redução do lead time surge como um dos principais objetivos adotados por uma empresa para competir no mercado, visto que estratégias baseadas no tempo visam fornecer respostas rápidas a seus clientes. Neste contexto, o presente trabalho tem como objetivo geral apresentar uma proposta para a redução de lead time a partir da aplicação dos conceitos e ferramentas da metodologia Quick Response Manufacturing (QRM) em uma empresa do setor de bens de capital. A fim de atingir o objetivo proposto, foi realizada uma revisão da literatura sobre a metodologia QRM e sistema POLCA e um estudo de caso em uma empresa que desenvolve e fabrica máquinas e equipamentos sob encomenda. Dessa maneira, analisaram-se as principais causas de espera no processo de fabricação de vasos de pressão e, por meio de propostas de melhorias, chegou-se aos resultados e ganhos esperados. Os resultados principais, além da redução de 40% do lead time, estão relacionados à melhoria de qualidade, aumento de responsabilidade no processo de fabricação e simplificação do controle de produção.

The demand for computational tools that are capable to reliably predict the behavior of a nuclear reactor core in a variety of static and dynamic conditions does inevitably require a proper qualification of these tools for the intended purposes. One of the qualification methods is the verification of the code in question. Hereby, the correct implementation of the applied model as well as its flawless implementation in the code are scrutinized. The present work concerns with benchmarking as a substantial part of the verification of the three-dimensional, multigroup neutron kinetics model employed in the transient code POLCA-T. The benchmarking is done by solving some specified and widely used space-time kinetics benchmark problems and comparing the results to those of other, established and well-proven spatial kinetics codes. It is shown that the obtained results are accurate and consistent with corresponding solutions of other codes. In addition, a sensitivity analysis is carried out with the objective to study the sensitivity of the POLCA-T neutronics to variations in different numerical options. It is demonstrated that the model is numerically stable and provide reproducible results for a wide range of various numerical settings. Thus, the model is shown to be rather insensitive to significant variations in input, for example. The other consequence of this analysis is that, depending on the treated transient, the computing costs can be reduced by, for instance, employing larger time-steps during the time-integration process or using a reduced number of iterations. Based on the outcome of this study, one can finally conclude that the POLCA-T neutron kinetics is modeled and implemented correctly and thus, the model is fully capable to perform the assigned tasks.

This study aims to improve the modeling of partial SCRAM in the BISON plant model for the Forsmark 2 nuclear reactor after power uprate. Validation of the BISON model against tests performed from March to May in 2013 have shown that this is one of the areas in which there is room for improvement. After partial SCRAM is performed, the model underestimates the reactor power, recirculation flow and steam flow when compared to the measurement data. In BISON the partial SCRAM is modeled using a relative control rod effect vector (ASC vector). The aim is to replace the old values in this vector to improve the model. The new model was shown to give an improved result for the reactor power, recirculation flow and steam flow. The study gives recommendations on how to apply the new model and what values of the relative control rod effect vector that can be used in the future.

Westinghouse Electric Sweden AB’s three-dimensional reactor core simulation program POLCA uses a large number of tables containing various fuel dependent data, such as cross sections, pin power maps with power distribution etc. POLCA uses quadratic and linear interpolation to extract the values needed for the simulation. However, finding the correct values to interpolate between takes time. This master thesis describes a method of compacting the tables by removing values, in order to shorten the needed simulation time. This is done so that no significant accuracy is lost in the interpolations. The method also finds deviant values and replaces these with new, interpolated values. The thesis shows that approximately 90 % of all values can be removed without losing significant accuracy. These results are however heavily dependent on the choice of accuracy loss criterion; a lower allowance for accuracy loss lowers the amount of values which can be removed sharply.

This project’s idea revolved around utilizing the most recent techniques in MachineLearning, Neural Networks, and Data processing to construct a model to be used asa tool to determine stability during core design work. This goal will be achieved bycollecting distribution profiles describing the core state from different steady statesin five burn-up cycles in a reactor to serve as the dataset for training the model. Anadditional cycle will be reserved as a blind testing dataset for the trained model topredict. The variables that will be the target for the predictions are the decay ratioand the frequency since they describe the core stability.The distribution profiles extracted from the core simulator POLCA7 were subjectedto many different Data processing techniques to isolate the most relevant variablesto stability. The processed input variables were merged with the decay ratio andfrequency for those cases, as calculated with POLCA-T. Two different MachineLearning models, one for each output parameter, were designed with Pytorch toanalyze those labeled datasets. The goal of the project was to predict the outputvariables with an error lower than 0.1 for decay ratio and 0.05 for frequency. Themodels were able to predict the testing data with an RMSE of 0.0767 for decay ratioand 0.0354 for frequency.Finally, the trained models were saved and tasked with predicting the outputparameters for a completely unknown cycle. The RMSE was even better forthe unknown cycle, with 0.0615 for decay ratio and 0.0257 for frequency,respectively. / Idén bakom detta projekt var att använda de senaste teknikerna inom maskininlärning, neurala nätverk och databehandling för att konstruera en modell att använda som ett verktyg för att avgöra stabilitet under härddesignsarbete. Detta mål kommer uppnås genom att samla distribueringsprofiler av härdens tillstånd från olika stabila lägen i fem förbränningscyklar (burn-up cycles) i en reaktor, som tjänar som en datamängd att träna modellen på.En sjätte förbränningscykel användes som en datamängd för ett blindprov som den tränade modellen ska förutse. Variablerna som kommer tjäna som mål för förutsägelserna är sönderfallsförhållandet (decay ratio) och frekvensen, då dessa beskriver härdens stabilitet. Distribueringsprofilerna som extraherats från härdsimulatorn POLCA7 utsattes för många olika databehandlingstekniker för att isolera de mest relevanta variablerna för stabilitet. De behandlade indatavariablerna blandades med sönderfallsförhållandet och frekvensen för dessa fall, som beräknats med POLCA-T. Två olika maskininlärningsmodeller, en för varje utdataparameter, designades med Pytorch för att analysera dessa märkta datamängder. Projektets mål var att förutse utdatavariablerna med ett fel under 0.1 för sönderfallsförhållandet och 0.05 för frekvensen. Modellerna lyckades förutse testdatan med en RMSE på 0.0767 för sönderfallsförhållande och 0.0354 för frekvensen.Slutligen sparades de tränade modellerna och gavs uppgiften att förutse utdataparametrarna för en komplett okänd cykel. För den okända cykeln var RMSE ännu lägre, med 0.0615 för sönderfallsförhållande och 0.0257 för frekvensen.

Ma thèse s'inscrit dans le cadre du programme POLCA (Pollution des Capitales Africaines). Elle a pour principal objectif de caractériser la pollution particulaire sur des sites " trafic " de deux capitales africaines Dakar (Sénégal) et Bamako (Mali) et d'étudier son impact toxicologique sur l'appareil respiratoire. La pollution particulaire urbaine, bien supérieure aux normes imposées par l'organisation mondiale de la santé, est mise en exergue en lien avec un trafic automobile anarchique et d'intenses combustions domestiques. Dans ce contexte, les questionnements scientifiques suivants ont pu être abordés : - Quelle est la spéciation chimique par classes de tailles des aérosols de combustion (carbone suie, carbone organique, inorganiques, métaux traces...) pour les sites " trafic " de Dakar et Bamako ? - Quelles sont les sources prédominantes agissant sur la composition chimique en aérosols ? Quelle est la toxicité de ces aérosols et le niveau de stress oxydant ? - Quels sont les liens entre composition des aérosols différenciés en tailles et marqueurs d'inflammation pour chaque type de source ? - Quels sont les liens entre expositions aux aérosols et doses dans l'appareil respiratoire ? - Pour traiter ces questions, je me suis attaché à l'étude des résultats des campagnes intensives de 2009 à Dakar et à Bamako auxquelles j'ai participé, principalement à l'analyse chimique complète des aérosols par classes de tailles, à la caractérisation physico-chimique complète de l'aérosol pour chaque site mais également à la détermination de ses différentes sources par des modèles multivariés (ACP et PMF). Ces études ont été associées à des mesures toxicologiques in vitro effectuées sur les aérosols prélevés sur ces mêmes sites. Ce croisement mesures physcico-chimique/mesure santé a permis d'approfondir les liens sources d'émissions/chimie de l'aérosol/granulométrie et impacts biologiques associés. Enfin, en parallèle aux mesures expérimentales développées dans POLCA, la thèse a permis la mise en œuvre du modèle DEPCLUNG (DEPosition, Clearance, LUNG) afin de convertir spéciation de l'aérosol par classe de taille ou EXPOSITIONS en concentrations d'espèces par classe de taille ou DOSES dans les divers compartiments de l'appareil respiratoire (trachée, bronches, bronchioles, alvéoles). C'est la conjonction des trois thèmes, caractérisation de la pollution urbaine particulaire en Afrique de l'Ouest et ses sources, son impact toxicologique et la modélisation des doses dans l'appareil respiratoire, qui constitue le caractère pluridisciplinaire innovant de la thèse.