Changes in the thermal growing season in Nordic countries during the past century and prospects for the future

Selostus: Termisen kasvukauden muutokset Pohjoismaissa viimeisen vuosisadan aikana ja tulevaisuudessa

Thermal conductivity of low-decomposed Sphagnum peat used as growth medium

Kasvualustana käytetyn heikosti maatuneen rahkaturpeen lämmönjohtavuus

Experimental thermal hydraulic studies on the enhancement of safety of LWRs

The safe use of nuclear power plants (NPPs) requires a deep understanding of the functioning of physical processes and systems involved. Studies on thermal hydraulics have been carried out in various separate effects and integral test facilities at Lappeenranta University of Technology (LUT) either to ensure the functioning of safety systems of light water reactors (LWR) or to produce validation data for the computer codes used in safety analyses of NPPs. Several examples of safety studies on thermal hydraulics of the nuclear power plants are discussed. Studies are related to the physical phenomena existing in different processes in NPPs, such as rewetting of the fuel rods, emergency core cooling (ECC), natural circulation, small break loss-of-coolant accidents (SBLOCA), non-condensable gas release and transport, and passive safety systems. Studies on both VVER and advanced light water reactor (ALWR) systems are included. The set of cases include separate effects tests for understanding and modeling a single physical phenomenon, separate effects tests to study the behavior of a NPP component or a single system, and integral tests to study the behavior of the whole system. In the studies following steps can be found, not necessarily in the same study. Experimental studies as such have provided solutions to existing design problems. Experimental data have been created to validate a single model in a computer code. Validated models are used in various transient analyses of scaled facilities or NPPs. Integral test data are used to validate the computer codes as whole, to see how the implemented models work together in a code. In the final stage test results from the facilities are transferred to the NPP scale using computer codes. Some of the experiments have confirmed the expected behavior of the system or procedure to be studied; in some experiments there have been certain unexpected phenomena that have caused changes to the original design to avoid the recognized problems. This is the main motivation for experimental studies on thermal hydraulics of the NPP safety systems. Naturally the behavior of the new system designs have to be checked with experiments, but also the existing designs, if they are applied in the conditions that differ from what they were originally designed for. New procedures for existing reactors and new safety related systems have been developed for new nuclear power plant concepts. New experiments have been continuously needed.

Modeling of Pressurizer Using APROS and TRACE Thermal Hydraulic Codes

Diplomityön tavoitteena on paineistimen yksityiskohtainen mallintaminen APROS- ja TRACE- termohydrauliikkaohjelmistoja käyttäen. Rakennetut paineistinmallit testattiin vertaamalla laskentatuloksia paineistimen täyttymistä, tyhjentymistä ja ruiskutusta käsittelevistä erilliskokeista saatuun mittausdataan. Tutkimuksen päätavoitteena on APROSin paineistinmallin validoiminen käyttäen vertailuaineistona PACTEL ATWS-koesarjan sopivia paineistinkokeita sekä MIT Pressurizer- ja Neptunus- erilliskokeita. Lisäksi rakennettiin malli Loviisan ydinvoimalaitoksen paineistimesta, jota käytettiin turbiinitrippitransientin simulointiin tarkoituksena selvittää mahdolliset voimalaitoksen ja koelaitteistojen mittakaavaerosta johtuvat vaikutukset APROSin paineistinlaskentaan. Kokeiden simuloinnissa testattiin erilaisia noodituksia ja mallinnusvaihtoehtoja, kuten entalpian ensimmäisen ja toisen kertaluvun diskretisointia, ja APROSin sekä TRACEn antamia tuloksia vertailtiin kattavasti toisiinsa. APROSin paineistinmallin lämmönsiirtokorrelaatioissa havaittiin merkittävä puute ja laskentatuloksiin saatiin huomattava parannus ottamalla käyttöön uusi seinämälauhtumismalli. Työssä tehdyt TRACE-simulaatiot ovat osa United States Nuclear Regulatory Commissionin kansainvälistä CAMP-koodinkehitys-ja validointiohjelmaa.

A computationally efficient shear deformable beam element for large deformation multibody applications

In this paper, a new two-dimensional shear deformable beam element based on the absolute nodal coordinate formulation is proposed. The nonlinear elastic forces of the beam element are obtained using a continuum mechanics approach without employing a local element coordinate system. In this study, linear polynomials are used to interpolate both the transverse and longitudinal components of the displacement. This is different from other absolute nodal-coordinate-based beam elements where cubic polynomials are used in the longitudinal direction. The accompanying defects of the phenomenon known as shear locking are avoided through the adoption of selective integration within the numerical integration method. The proposed element is verified using several numerical examples, and the results are compared to analytical solutions and the results for an existing shear deformable beam element. It is shown that by using the proposed element, accurate linear and nonlinear static deformations, as well as realistic dynamic behavior, can be achieved with a smaller computational effort than by using existing shear deformable two-dimensional beam elements.

Validation Studies of Thermal-hydraulic Code for Safety Analysis of Nuclear Power Plants

This thesis gives an overview of the validation process for thermal hydraulic system codes and it presents in more detail the assessment and validation of the French code CATHARE for VVER calculations. Three assessment cases are presented: loop seal clearing, core reflooding and flow in a horizontal steam generator. The experience gained during these assessment and validation calculations has been used to analyze the behavior of the horizontal steam generator and the natural circulation in the geometry of the Loviisa nuclear power plant. The cases presented are not exhaustive, but they give a good overview of the work performed by the personnel of Lappeenranta University of Technology (LUT). Large part of the work has been performed in co-operation with the CATHARE-team in Grenoble, France. The design of a Russian type pressurized water reactor, VVER, differs from that of a Western-type PWR. Most of thermal-hydraulic system codes are validated only for the Western-type PWRs. Thus, the codes should be assessed and validated also for VVER design in order to establish any weaknesses in the models. This information is needed before codes can be used for the safety analysis. Theresults of the assessment and validation calculations presented here show that the CATHARE code can be used also for the thermal-hydraulic safety studies for VVER type plants. However, some areas have been indicated which need to be reassessed after further experimental data become available. These areas are mostly connected to the horizontal stem generators, like condensation and phase separation in primary side tubes. The work presented in this thesis covers a large numberof the phenomena included in the CSNI code validation matrices for small and intermediate leaks and for transients. Also some of the phenomena included in the matrix for large break LOCAs are covered. The matrices for code validation for VVER applications should be used when future experimental programs are planned for code validation.

Experimental insights into deformation dynamics and intermittency in rapid granular shear flows

This work concerns the experimental study of rapid granular shear flows in annular Couette geometry. The flow is induced by continuous driving of the horizontal plate at the top of the granular bed in an annulus. The compressive pressure, driving torque, instantaneous bed height and rotational speed of the shearing plate are measured. Moreover, local stress fluctuations are measured in a medium made of steel spheres 2 and 3 mm in diameter. Both monodisperse packing and bidisperse packing are investigated to reveal the influence of size diversity in intermittent features of granular materials. Experiments are conducted in an annulus that can contain up to 15 kg of spherical steel balls. The shearing granular medium takes place via the rotation of the upper plate which compresses the material loaded inside the annulus. Fluctuations of compressive force are locally measured at the bottom of the annulus using a piezoelectric sensor. Rapid shear flow experiments are pursued at different compressive forces and shear rates and the sensitivity of fluctuations are then investigated by different means through monodisperse and bidisperse packings. Another important feature of rapid granular shear flows is the formation of ordered structures upon shearing. It requires a certain range for the amount of granular material (uniform size distribution) loaded in the system in order to obtain stable flows. This is studied more deeply in this thesis. The results of the current work bring some new insights into deformation dynamics and intermittency in rapid granular shear flows. The experimental apparatus is modified in comparison to earlier investigations. The measurements produce data for various quantities continuously sampled from the start of shearing to the end. Static failure and dynamic shearing ofa granular medium is investigated. The results of this work revealed some important features of failure dynamics and structure formation in the system. Furthermore, some computer simulations are performed in a 2D annulus to examine the nature of kinetic energy dissipation. It is found that turbulent flow models can statistically represent rapid granular flows with high accuracy. In addition to academic outcomes and scientific publications our results have a number of technological applications associated with grinding, mining and massive grain storages.

Development of rotating drum under mechanical and thermal load

A variable temperature field sets exacting demands to the structure under mechanical load. Most of all the lifetime of the rotating drum structure depends on temperature differences between parts inside the drum. The temperature difference was known because of the measurements made before. The list of demands was created based on customers’ needs. The limits of this paper were set to the inner structure of the drum. Creation of ideas for the inner structure was started open minded. The main principle in the creation process was to create new ideas for the function of the product with the help of sub-functions. The sub-functions were created as independent as possible. The best sub-functions were combined together and the new working principles were created based on them. Every working principle was calculated separately and criticized at the end of the calculation process. The main objective was to create the new kind of structure, which is not based too much to the old, inoperative structure. The affect of own weight of the inner structure to the stress values was quite small but it was also taken into consideration when calculating the maximum stress value of the structure. Because of very complex structures all of the calculations were made with the help of the ProE – Mechanica software. The fatigue analyze was made also for the best structure solution.

The Sottunga-Jurmo shear zone : structure and deformation history of a crustal-scale ductile shear zone in SW Finland

The aim of this study is to gain a better understanding of the structure and the deformation history of a NW-SE trending regional, crustal-scale shear structure in the Åland archipelago, SW Finland, called the Sottunga-Jurmo shear zone (SJSZ). Approaches involving e.g. structural geology, geochronology, geochemistry and metamorphic petrology were utilised in order to reconstruct the overall deformation history of the study area. The study therefore describes several features of the shear zone including structures, kinematics and lithologies within the study area, the ages of the different deformation phases (ductile to brittle) within the shear zone, as well as some geothermobarometric results. The results indicate that the SJSZ outlines a major crustal discontinuity between the extensively migmatized rocks NE of the shear zone and the unmigmatised, amphibolite facies rocks SW of the zone. The main SJSZ shows overall dextral lateral kinematics with a SW-side up vertical component and deformation partitioning into pure shear and simple shear dominated deformation styles that was intensified toward later stages of the deformation history. The deformation partitioning resulted in complex folding and refolding against the SW margin of the SJSZ, including conical and sheath folds, and in a formation of several minor strike-slip shear zones both parallel and conjugate to the main SJSZ in order to accommodate the regional transpressive stresses. Different deformation phases within the study area were dated by SIMS (zircon U-Pb), ID-TIMS (titanite U-Pb) and 40Ar/39Ar (pseudotachylyte wholerock) methods. The first deformation phase within the ca. 1.88 Ga rocks of the study area is dated at ca. 1.85 Ga, and the shear zone was reactivated twice within the ductile regime (at ca. 1.83 Ga and 1.79 Ga), during which the strain was successively increasingly partitioned into the main SJSZ and the minor shear zones. The age determinations suggest that the orogenic processes within the study area did not occur in a temporal continuum; instead, the metamorphic zircon rims and titanites show distinct, 10-20 Ma long breaks in deformation between phases of active deformation. The results of this study further imply slow cooling of the rocks through 600-700ºC so that at 1.79 Ga, 2 the temperature was still at least 600ºC. The highest recorded metamorphic pressures are 6.4-7.1 kbar. At the late stages or soon after the last ductile phase (ca. 1.79 Ga), relatively high-T mylonites and ultramylonites were formed, witnessing extreme deformation partitioning and high strain rates. After the rocks reached lower amphibolite facies to amphibolite-greenschist facies transitional conditions (ca. 500-550ºC), they cooled rapidly, probably due to crustal uplift and exhumation. The shear zone was reactivated at least once within the semi-brittle to brittle regime between ca. 1.79 Ga and 1.58 Ga, as evidenced by cataclasites and pseudotachylytes. In summary, the results of this study suggest that the Sottunga-Jurmo shear zone (and the South Finland shear zone) defines a major crustal discontinuity, and played a central role in accommodating the regional stresses during and after the Svecofennian orogeny.

Supplier Energy Audits in Thermal Power Plants

This master’s thesis handles an operating model for an electric equipment supplier conducted sale oriented energy audit for pumping, fan and other motor applications at power plants. The study goes through the largest factors affecting internal electricity use at a power plant, finds an energy audit –like approach for the basis of information gathering and presents the information needed for conducting the analysis. The model is tested in practice at a kraft recovery boiler of a chemical pulping mill. Targets chosen represent some of the largest electric motor applications in the boiler itself and in its fuel handling. The energy saving potential of the chosen targets is calculated by simulating the energy consumption of the alternatives for controlling the targets, and thereafter combining the information with the volume flow duration curve. Results of the research are somewhat divaricated, as all the information needed is not available in the automation system. Some of the targets could be simulated and their energy saving potential calculated quite easily. At some of the targets chosen the monitoring was not sufficient enough for this and additional measurements would have been needed to base the calculations on. In traditional energy audits, energy efficiency of pump and fan applications is not necessarily examined. This means that there are good possibilities for developing the now presented targeted energy audit procedure basis further.

The evaluation of hazardous gas components caused by the thermal degradation of plant oils and animal fats

Neste Oil has introduced plant oils and animal fats for the production of NExBTL renewable diesel, and these raw materials differ from the conventional mineral based oils. One subject of new raw materials study is thermal degradation, or in another name pyrolysis, of these organic oils and fats. The aim of this master’s thesis is to increase knowledge on thermal degradation of these new raw materials, and to identify possible gaseous harmful thermal degradation compounds. Another aim is to de-termine the health and environmental hazards of identified compounds. One objective is also to examine the formation possibilities of hazardous compounds in the produc-tion of NExBTL-diesel. Plant oils and animal fats consist mostly of triglycerides. Pyrolysis of triglycerides is a complex phenomenon, and many degradation products can be formed. Based on the literature studies, 13 hazardous degradation products were identified, one of which was acrolein. This compound is very toxic and dangerous to the environment. Own pyrolysis experiments were carried out with rapeseed and palm oils, and with a mix-ture of palm oil and animal fat. At least 12 hazardous compounds, including acrolein, were analysed from the gas phase. According to the experiments, the factors which influence on acrolein formation are the time of the experiment, the sphere (air/hydrogen) in which the experiment is carried out, and the characteristics of the used oil. The production of NExBTL-diesel is not based on pyrolysis. This is why thermal degradation is possible only when abnormal process conditions prevail.

Thermal-Hydraulic Studies on the Safety Of VVER-440 Type Nuclear Power Plants

This thesis includes several thermal hydraulic analyses related to the Loviisa WER 440 nuclear power plant units. The work consists of experimental studies, analysis of the experiments, analysis of some plant transits and development of a calculational model for calculation of boric acid concentrations in the reactor. In the first part of the thesis, in the case of won of boric acid solution behaviour during long term cooling period of LOCAs, experiments were performed in scaled down test facilities. The experimental data together with the results of RELAPS/MOD3 simulations were used to develop a model for calculations of boric acid concentrations in the reactor during LOCAs. The results of calculations showed that margins to critical concentrations that would lead to boric acid crystallization were large, both in the reactor core and in the lower plenum. This was mainly caused by the fact that water in the primary cooling circuit includes borax (Na)BsO,.IOHZO), which enters the reactor when ECC water is taken from the sump and greatly increases boric acid solubility in water. In the second part, in the case of simulation of horizontal steam generators, experiments were performed with PACTEL integral test loop to simulate loss of feedwater transients. The PACTEL experiments, as well as earlier REWET III natural circulation tests, were analyzed with RELAPS/MOD3 Version Sm5 code. The analysis showed that the code was capable of simulating the main events during the experiments. However, in the case of loss of secondary side feedwater the code was not completely capable to simulate steam superheating in the secondary side of the steam generators. The third part of the work consists of simulations of Loviisa VVER reactor pump trip transients with RELAPSlMODI Eur, RELAPS/MOD3 and CATHARE codes. All three codes were capable to simulate the two selected pump trip transients and no significant differences were found between the results of different codes. Comparison of the calculated results with the data measured in the Loviisa plant also showed good agreement.

High pressure compression of filter cakes

The purpose of this thesis was to investigate the compression of filter cakes at high filtration pressures with five different test materials and to compare the energy consumption of high pressure compression with the energy consumption of thermal drying. The secondary target of this study was to investigate the particle deformation of test materials during filtration and compression. Literature part consists of basic theory of filtration and compression and of the basic parameters that influence the filtration process. There is also a brief description about all of the test materials including their properties and their industrial production and processing. Theoretical equations for calculating the energy consumptions of the filtrations at different conditions are also presented. At the beginning of the experiments at experimental part, the basic filtration tests were done with all the five test materials. Filtration tests were made at eight different pressures, from 6 bars up to 100 bars, by using piston press pressure filter. Filtration tests were then repeated by using a cylinder with smaller slurry volume than in the first series of filtration tests. Separate filtration tests were also done for investigating the deformation of solid particles during filtration and for finding the optimal curve for raising the filtration pressure. Energy consumption differences between high pressure filtration and ideal thermal drying process were done partly experimentally and partly by using theoretical calculation equations. By comparing these two water removal methods, the optimal ranges for their use were found considering their energy efficiency. The results of the measurements shows that the filtration rate increased and the moisture content of the filter cakes decreased as the filtration pressure was increased. Also the porosity of the filter cakes mainly decreased when the filtration pressure was increased. Particle deformation during the filtration was observed only with coal particles.