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.

The thesis aims at contributing to clarify broad conjectures on growth, such as, (i) the extent to which growth constitutes an imperative for the firm, and (ii) what leads some firms to enjoy continuing growth and a continued existence, while others, after experiencing continuing growth, end up contracting and decaying. As a result, the thesis seeks to develop a deeper understanding of the mechanisms fostering and precluding growth, while also identifying challenges and opportunities in managing growth. / The thesis comprises four interrelated essays: (i) Chandler on the growth of the firm---this essay scrutinizes The Visible Hand (Chandler, 1977) seeking to answer the question "What is Chandler's theory on how and why did the modern business enterprise (MBE) appear and grow?" Four processes are identified---MBE formation, MBE development, industry formation, industry development. Their analysis within a process-oriented view (Mohr, 1982) discloses chains of necessary conditions in growth-related processes. Moreover, two growth-related dilemmas are advanced and the firm-industry co-evolution is explored. (ii) Identifying the building blocks of growth dynamics---this essay addresses the question "Which are the basic processes of change that form the dynamics of growth?" Drawing on Mario Bunge's philosophy (1973--1989; 1979), a framework of qualitatively different modes of change is derived. The framework allows the identification of elementary units of the growth dynamics. These comprise the following types: quantitative, qualitative (dialectical), goal-directed, interactional, causal, structural, random. In addition, complex units of growth dynamics made up of combinations of elementary units are also advanced: evolutionary motor of firm growth, co-evolutionary motor of growth relating firm and industry, and different instances of continuing growth motors. (iii) Describing growth trajectories of firms---the question "How can growth trajectories be represented?" is addressed in this essay. An indicator of size, which automatically adjusts for inflationary and deflationary changes in currency value is proposed. This indicator enables the drawing of growth trajectories of firms in the economy over long periods of time. (iv) Growth trajectories of General Electric and Westinghouse: a comparative study---this essay addresses the question "Why do some firms experience continuing growth and continued existence while others decay and disappear?" The growth trajectories of

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.

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In this master thesis an input-model of a Nordic BWR power plant has been developed in APROS. The plant model contains key systems and major thermohydraulic components of the steam cycle, including I&C systems (i.e. power, pressure, level and flow controls). The plant model is primarily designed for balance of plant studies at discrete power levels. The input-model of the power plant focuses especially on the steam cycle which is crucial for analysing water and steam behaviour and its influence on the reactor power. At the current stage, the model primarily handles steady-state conditions of full-power operation, which has been the design point. It has also been shown that reduced-power operation can be simulated with a reasonable trendline of pressure and temperature progression over facility components. / Inom ramen för examensarbete har en indatafil (modell) av en nordisk kokvattenreaktor, BWR, utvecklats i simuleringsverktyget APROS. Anläggningsmodellen är främst utformad för att simulera diskreta effektnivåer och innehåller viktiga system och termohydrauliska komponenter som ingår i ångcykeln, inklusive instrumenterings- och kontrollutrustning (dvs. effekt-, tryck-, nivå- och flödesreglering). Fokus har lagts särskilt på att få till en bra representation av ångcykeln, vilket är avgörande för analys av vatten- och ångbeteendet och dess påverkan på reaktoreffekten. Modellen kan främst användas för simulering av jämviktstillstånd vid full effektdrift och till en viss grad även reducerad effektdrift.

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The safety performance of nuclear power reactors is a very important factor in evaluating nuclear energy sustainability. Improving the safety performance of nuclear reactors can enhance nuclear energy sustainability as it will improve the environmental indicator used to evaluate the overall sustainability of nuclear energy. Great interest is given now to advanced nuclear reactors especially those using passive safety components. Investigation of the improvement in nuclear safety using advanced reactors was done by comparing the safety performance of a conventional reactor which uses active safety systems, such as Pressurized Water Reactor (PWR), with an advanced reactor which uses passive safety systems, such as AP1000, during a design basis accident, such as Loss of Coolant Accident (LOCA), using the PCTran as a simulation code. To assess the safety performance of PWR and AP1000, the “Global Safety Index” GSI model was developed by introducing three indicators: probability of accident occurrence, performance of safety system in case of an accident occurrence, and the consequences of the accident. Only the second indicator was considered in this work. A more detailed model for studying the performance of passive safety systems in AP1000 was developed. That was done using SCDAPSIM/RELAP5 code as it is capable of modelling design basis accidents (DBAs) in advanced nuclear reactors.

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