The removal of heat from the containment building is an important consideration in the design of a nuclear power plant. In this investigation a simple rectangular natural circulation loop was simulated to determine whether it could possibly be used to remove usable quantities of heat from a containment building. The loop had a vertical pipe on the inside and outside of the containment building. These pipes acted as heat exchangers. Single phase and two phase cases were simulated by imposing a temperature on the respective vertical leg pipe walls and determining the heat absorption from the containment building. The heat was conveyed from the inside of the building to the outside via the natural circulation phenomenon. A literature study was done to cover topics relevant to this investigation. A theoretical model using conservation equations and control volumes was derived. This model was based largely on knowledge gleaned from the literature study. The theoretical model was a simple homogenous model, which was sufficiently detailed for a conceptual investigation. The theoretical model was then manipulated into a form suitable for use in a computer simulation program. Simplifications were made to the simulation model and underlying theory due to the nature of the investigation. The simulation model was validated against published experimental results. During the simulation phase a number of cases were investigated. These cases were divided into base cases and parametric studies. During the base case simulations the change of key fluid variables along the loop was examined. During the parametric studies the hot and cold leg inside wall temperatures, loop geometry and pipe diameter were varied. The effect of these parameters on the heat absorption from the containment was determined. The simulations showed that with the current assumptions about 75 to 120 of the natural circulation loops are needed depending on their geometry and containment conditions. The heat removal rates that were calculated varied from 50 kW to 600 kW for a single loop. As explained in the final chapter, there are many factors that influence the results obtained. The natural circulation concept was deemed to be able to remove usable quantities of heat from the containment building. / Thesis (M.Ing. (Nuclear Engineering))--North-West University, Potchefstroom Campus, 2012.

The removal of heat from the containment building is an important consideration in the design of a nuclear power plant. In this investigation a simple rectangular natural circulation loop was simulated to determine whether it could possibly be used to remove usable quantities of heat from a containment building. The loop had a vertical pipe on the inside and outside of the containment building. These pipes acted as heat exchangers. Single phase and two phase cases were simulated by imposing a temperature on the respective vertical leg pipe walls and determining the heat absorption from the containment building. The heat was conveyed from the inside of the building to the outside via the natural circulation phenomenon. A literature study was done to cover topics relevant to this investigation. A theoretical model using conservation equations and control volumes was derived. This model was based largely on knowledge gleaned from the literature study. The theoretical model was a simple homogenous model, which was sufficiently detailed for a conceptual investigation. The theoretical model was then manipulated into a form suitable for use in a computer simulation program. Simplifications were made to the simulation model and underlying theory due to the nature of the investigation. The simulation model was validated against published experimental results. During the simulation phase a number of cases were investigated. These cases were divided into base cases and parametric studies. During the base case simulations the change of key fluid variables along the loop was examined. During the parametric studies the hot and cold leg inside wall temperatures, loop geometry and pipe diameter were varied. The effect of these parameters on the heat absorption from the containment was determined. The simulations showed that with the current assumptions about 75 to 120 of the natural circulation loops are needed depending on their geometry and containment conditions. The heat removal rates that were calculated varied from 50 kW to 600 kW for a single loop. As explained in the final chapter, there are many factors that influence the results obtained. The natural circulation concept was deemed to be able to remove usable quantities of heat from the containment building. / Thesis (M.Ing. (Nuclear Engineering))--North-West University, Potchefstroom Campus, 2012.

Målen med denna uppsats var att studera två aspekter av temperatur inducerade spänningar med referens till kärnkraftsanläggningen Forsmark F1. Ena aspekten inkluderade den termiska kyleffekten av de ventilerade spännkabelrören i cylinderväggen. Det var av intresse att studera om den termiska kyleffekten av de ventilerade spännkabelrören hade en positiv global effekt som var relevant att beakta i globala tredimensionella modeller. Den andra aspekten inkluderade inverkan av ingjutet stål i den övreringplattan. Med syftet att studera om ingjutet stål var en aspekt som ansågs nödvändigt att beakta i transienta analyser.   Huvudanalyseringsverktyg var finita element metoden (FEM), genom användning av det kommersiellt tillgängliga finita element programmet SOLVIA.   Inverkan av den termiska kyleffekten av de ventilerade spännkabelrören indikerade en spännings reducerande effekt, med reducerade zoner av sprucken betong i cylinderväggen vid förhöjda temperaturer. Inverkan av ingjutet stål indikerade ökade temperaturskillnader mellan det ingjutna stålet och den omgivande betongen, med sprucken betong lokalt mellan stålet och betongen vid förhöjda temperaturer. Den termiska kyleffekten av de ventilerade spännkabelrören ansågs relevant att beakta i globala tredimensionella modeller. Ingjutet stål ansågs vara nödvändigt att inkludera i transienta analyser. / The aims of this thesis were to study two aspects of temperature induced stresses with reference to the nuclear power plant Forsmark F1. One aspect included the thermal cooling effect of the ventilated tendon ducts in the cylinder wall. It was of interest to study if the thermal cooling effect of the ventilated tendon ducts had a positive global effect which was relevant to consider in global three-dimensional models. The other aspect included the influence of embedded steel in the upper ring slab. With the purpose to study if embedded steel was an aspect that was considered necessary to include in transient analyses.   The used main analysis tool was the finite element method (FEM), through the use of the commercially available finite element program SOLVIA.   The influence of the thermal cooling effect of the ventilated tendon ducts indicated a stress reducing effect, with reduced cracked concrete in the cylinder wall at elevated temperatures. The influence of embedded steel indicated increased temperature differences between the embedded steel and the surrounding concrete, with cracked concrete locally between the steel and the concrete at elevated temperatures. The thermal cooling effect of the ventilated tendon ducts was considered relevant to consider in global three-dimensional models. Embedded steel was considered necessary to include in transient analyses.

<p>The research presented in this dissertation investigates the influence of soil-structure<br> interaction on seismic isolation of nuclear reactor vessels using numerical simulations. This<br> research is motivated by the nuclear industry searching for viable solutions to standardize<br> the design of reactor vessels. Seismic isolation of reactor vessels is a potential solution as it<br> enables deployment of standardized reactor vessels irrespective of site seismic hazard<br> thereby saving time and cost by allowing large-scale factory fabrication of standard<br> modules and by eliminating the need for repeated approval of reactor vessel design. Seismic<br> isolation is also a technology that has matured from successful implementation in buildings<br> and bridges allowing easier transition to nuclear applications. Currently, the<br> implementation of component-level seismic isolation in nuclear industry is challenging due<br> to gaps in research and lack of specific guidelines.</p> <p><br></p> <p><br> In this research, the effectiveness and potential limitations of using conventional friction<br> pendulum bearings for component-level isolation are investigated based on conceptual<br> numerical models of seismically isolated reactor vessels at different nuclear power plant<br> sites subject to a variety of ground motions. The numerical modeling and analysis<br> approach presented in this research are checked using experimental data and results from<br> multiple numerical codes to ensure reliability of the obtained analysis results.</p> <p><br></p> <p><br> Within the scope of this study, it is found that slender vessels are particularly vulnerable<br> to rotational acceleration at the isolation interface. Rotational acceleration at the isolation<br> interface is caused by rotation at the foundation level of the containment building housing<br> the isolated reactor vessel and by excitation of higher horizontal translational modes of the<br> seismically isolated system. Rotation of the building foundation increases with decrease in<br> shear wave velocity of the soil surrounding the building foundation. When the containment<br> building is embedded below the soil surface, the effect of embedment on peak horizontal<br> acceleration of the isolated vessel depends on the amount of increase in shear wave velocity<br> at the foundation level of the building. When embedment does not result in any change in<br> shear wave velocity, it is found to have negligible impact on the acceleration response of the<br> isolated vessel.</p> <p><br></p> <p>  The optimum location to support a vessel for seismic isolation is found to be on a plane<br> passing through its center of mass. It minimizes horizontal acceleration in the isolated<br> vessel as well as the tendency of isolator to uplift. Isolator uplift and exceedence of<br> displacement capacity of the isolator during extreme events are possible drawbacks in using<br> seismic isolation technology since they produce impact forces due to uplift and<br> re-engagement of the isolator or due to collision between the isolated system and the moat<br> wall. If such cases are avoided, seismic isolation of reactor vessel could provide more than<br> 50% reduction in peak acceleration of vessel except for low-intensity motions that do not<br> engage the isolator.<br>  <br>  </p>