Showing papers by "Vattenfall published in 2007"

Key Elements in a Framework for Land Use Impact Assessment Within LCA

Abstract: Background, Aim and Scope Land use by agriculture, forestry, mining, house-building or industry leads to substantial impacts, particularly on biodiversity and on soil quality as a supplier of life support functions. Unfortunately there is no widely accepted assessment method so far for land use impacts. This paper presents an attempt, within the UNEP-SETAC Life Cycle Initiative, to provide a framework for the Life Cycle Impact Assessment (LCIA) of land use. Materials and Methods: This framework builds from previous documents, particularly the SETAC book on LCIA (Lindeijer et al. 2002), developing essential issues such as the reference for occupation impacts; the impact pathways to be included in the analysis; the units of measure in the impact mechanism (land use interventions to impacts); the ways to deal with impacts in the future; and bio-geographical differentiation. Results: The paper describes the selected impact pathways, linking the land use elementary flows (occupation; transformation) and parameters (intensity) registered in the inventory (LCI) to the midpoint impact indicators and to the relevant damage categories (natural environment and natural resources). An impact occurs when the land properties are modified (transformation) and also when the current man-made properties are maintained (occupation). Discussion: The size of impact is the difference between the effect on land quality from the studied case of land use and a suitable reference land use on the same area (dynamic reference situation). The impact depends not only on the type of land use (including coverage and intensity) but is also heavily influenced by the bio-geographical conditions of the area. The time lag between the land use intervention and the impact may be large; thus land use impacts should be calculated over a reasonable time period after the actual land use finishes, at least until a new steady state in land quality is reached. Conclusions: Guidance is provided on the definition of the dynamic reference situation and on methods and time frame to assess the impacts occurring after the actual land use. Including the occupation impacts acknowledges that humans are not the sole users of land. Recommendations and Perspectives: The main damages affected by land use that should be considered by any method to assess land use impacts in LCIA are: biodiversity (existence value); biotic production potential (including soil fertility and use value of biodiversity); ecological soil quality (including life support functions of soil other than biotic production potential). Bio-geographical differentiation is required for land use impacts, because the same intervention may have different consequences depending on the sensitivity and inherent land quality of the environment where it occurs. For the moment, an indication of how such task could be done and likely bio-geographical parameters to be considered are suggested. The recommendation of indicators for the suggested impact categories is a matter of future research.

Best Practice Guidelines for the use of CFD in Nuclear Reactor Safety Applications

Abstract: In May 2002, an 'Exploratory Meeting of Experts to Define an Action Plan on the Application of Computational Fluid Dynamics (CFD) Codes to Nuclear Reactor Safety Problems' was held at Aix-en-Provence, France. One of three recommended actions was the formation of this writing group to report on the need for guidelines for use of CFD in single phase Nuclear Reactor Safety (NRS) applications. CSNI approved this writing group at the end of 2002, and work began in March 2003. A final report was submitted to GAMA in September 2004, summarizing existing Best Practice Guidelines (BPG) for CFD, and recommending creation of a BPG document for Nuclear Reactor Safety (NRS) applications. The present document is intended to provide an internally complete set of guidelines for a range of single phase applications of CFD to NRS problems. However, it is not meant to be comprehensive; it is recognized that for any specific application a higher level of specificity is possible on questions of nodalization, model selection, and validation. This document should provide direct guidance on the key considerations in known single phase applications, and general directions for resolving remaining details. The intent is that it will serve as a template for further application specific (e.g. PTS, induced break) BPG documents that will provide much more detailed information and examples. The document begins with a summary of NRS related CFD analysis in countries represented by the authors. Chapter 3 deals with definition of the problem and its solution approach. This includes isolation of the portion of the NRS problem most in need of CFD, and use of a classic thermal hydraulic (TH) safety code to provide boundary conditions for the CFD based upon less detailed simulation of the balance of plant. Chapter 4 provides guidance in choosing between various options, and also discusses use of a transient calculation with tightly coupled CFD and TH codes. Chapter 5 discusses selection of physical models available as user options. As is appropriate for single phase CFD, most of the emphasis is on selection of turbulence models. Recommendations are provided for high level selection between Reynolds Averaged Navier Stokes (RANS), Large Eddy Simulation (LES), and hybrid approaches such as Detached Eddy Simulation (DES). Chapter 7 focuses on the numerical approximations available to solve the flow equations. Guidelines are provided for nodalization, and for choice of discrete approximations to the differential equations. Guidance is also given on convergence of iterative solutions, and numerical techniques for following free surfaces. Chapter 7 discusses general assessment strategy. Chapter 8 covers approaches to limiting errors associated with discretization and numerical solution methods (verification). This step is a necessary precursor to quantifying errors associated with physical models (validation) as described in Chapter 9. Guidance on documentation is provided in Chapter 10. Chapter 11 provides some examples of NRS applications; the first two examples are boron dilution and pressurized thermal shock; the third example explores the use of Fluent for simulation of dry cask storage of spent fuel (this example is highly suited to single phase CFD analysis)

Alkali deactivation of high-dust SCR catalysts used for NOx reduction exposed to flue gas from 100 MW-scale biofuel and peat fired boilers: Influence of flue gas composition

Abstract: Deactivation of vanadium–titanium deNO x SCR (selective catalytic reduction) catalysts in high-dust position have been investigated in three 100 MW-scale boilers during biofuel and peat combustion. The deactivation of the catalyst samples has been correlated to the corresponding flue gas composition in the boilers. Too investigate the effect on catalyst deactivation a sulphate-containing additive was sprayed into one of the furnaces. Increased alkali content on the SCR catalyst samples decreased the catalytic deNO x activity. The study has shown a linear correlation between exposure time in the boilers and alkali concentration (mainly potassium) on the samples. The results imply that mainly alkali in ultra fine particles (

Experimental Verification of Novel Pellet Model Using a Single Pelleter Unit

Abstract: Pelletization of biomass for bioenergy purposes has established itself as an important step toward a reduction in the emissions of greenhouse gases A novel pellet model describing the pressure forces in a press channel of a pellet mill has previously been published The model gives a theoretical explanation of how the biomass-specific parameters, such as the friction coefficient and Poisson's ratio, influence the pelletizing pressure The model showed that the pelletizing pressure increases exponentially as a function of the channel length In the present paper, the pellet model is verified experimentally When the back pressure needed to press pellets of different lengths out of the press channel is measured, it is shown that the pelletizing pressure does increase exponentially as a function of the pellet length Second, the back pressures of the hardwood beech are higher than the corresponding pressures of the softwood pine for all tested pellet lengths Least-squares fit of the model to the data shows that the fitted parameters are in agreement with values from the literature The procedure for using a single pelleter unit as a means for simulating an industrial pelletizing process in a controllable way is described

Dependence of XLPE insulated power cable wave propagation characteristics on design parameters

Abstract: Propagation losses occur in medium voltage power cables as pulses propagate through them. Since cables have many components, these can make different contributions to the propagation losses. The relative contributions of the conductors, insulation and semi-conducting screens to the propagation characteristics of the cable are analyzed. The propagation characteristics of the cables are studied by a developed "approximate" model providing analytical expressions that can quantify the contributions to the losses by the different parts of the conductor and dielectric system. The model is compared with an "exact" model and is tested on four cables

Analysis of the Ductile-to-Brittle Transition Temperature Shift in a Commercial Power Plant With High Nickel Containing Weld Material

Abstract: Plant specific surveillance programs that ideally include all relevant materials and materials combinations that are subjected to neutron irradiation during operation address the degradation due to irradiation of the reactor pressure vessel material for nuclear electric power plants. Plant specific surveillance programs are not unique to the two power plants treated in this study. The current Swedish regulatory system does, however, call for a fairly rigid approach within the surveillance program. In the Swedish case, this means that there is a plant specific predetermined inspection∕test program that has to be followed in order to verify the operability of the power plant and also to verify the operational limits with respect to pressure∕temperature effects on a repetitive basis. The two pressurized water reactor plants Ringhals 3 and 4 have in common that the weld metal used for the butt welds of the reactor pressure vessel is a high nickel type material, above the current limits of the NUREG Reg. Guide 1.99, rev. 2. In the original state, the high nickel content provides excellent fracture toughness in the unirradiated material condition and a low ductile-to-brittle transformation temperature (DBTT). It has, however, been highlighted in several studies that high nickel materials exhibit a very large DBTT shift as a consequence of irradiation, and also that the precipitates that form during the irradiation are not as easily controlled during a heat treatment to remove the irradiation damage as are the copper rich clusters. This paper will present the current state of the art regarding these effects as observed in the weld metal specimens. The paper will present the results from the Charpy V notched and fracture mechanics specimen test encapsulated in the Ringhals Units 3 and 4 surveillance programs. The results from the Ringhals Units 3 and 4 surveillance programs show that there is a need for corrective action to be taken in order to ensure 60 y of operability for the two power plants.

Power System Static Voltage Stability Analysis Considering all Active and Reactive Power Controls - Singular Value Approach

Abstract: This paper presents a novel approach for analyzing power system static voltage stability considering all possible active and reactive power controls based on the multi-input multi-output (MIMO) transfer function. By applying the voltage magnitudes of critical buses as output and feasible controls as input signals, the MIMO transfer function of multi-machine power system can be developed. The analyses are carried out by means of the singular value decomposition (SVD). The proposed approach takes the advantages of the classical static voltage stability analysis and the modern multi-variable feedback control theory. Not only the influences of reactive power controls on the static voltage stability, which can be achieved by the classic method, the influence of active power modulation can also be analyzed. The output singular vectors provide an overview of the most critical buses that affected by the static voltage stability. The magnitudes of the input singular vectors show that which input signal has the largest effect on the most critical bus. The proposed approach is simple and easy to be implemented into large power systems.

Wave propagation on power cables with special regard to metallic screen design

Abstract: The high frequency properties of coaxial power cables are modeled using time- and frequency-domain numerical simulations. This is required due to the complex helical structure of the outer metallic screen. The finite element (FEM) and finite difference time domain methods (FDTD) have been employed to study the effect of screen spiralization. It is established that this screen design causes a dependence of the cable high frequency characteristics on the surrounding medium. Analytical model based on modal analysis of wave propagation in coaxial cables confirms the numerical observations.

Influence on the stability of generator rotors due to radial and tangential magnetic pull force

Abstract: Forces due to nonuniform airgaps in rotating electrical machines have been a research topic for over 100 years. However, most research in the area of rotating electrical machines has been performed on motors. Large forces in hydropower generators can lead to expensive damage and failures. Therefore, it is of interest to calculate the forces that arise in a large synchronous generator with an eccentric rotor and study the influence these forces have on the stability of the generator rotor. A 74 MVA synchronous hydropower generator was simulated with an eccentric rotor, using a time-stepping finite-element technique. The forces were calculated using Coulomb's virtual-work method and simulations were performed for no-load and load cases. The resulting force was found to be reduced significantly when a damper winding was taken into account. An interesting effect of the rotor damper winding was that it reduced the eccentricity force and introduced a force component perpendicular to the direction of eccentricity. The results from the finite-element simulations were used to determine how the forces affect the stability of the generator rotor. Damped natural eigenfrequencies and damping ratio for load and no-load conditions are presented. When applying the forces computed in the time-dependent model, the damped natural eigenfrequencies were found to increase and the stability of the generator rotor was found to be reduced compared with when the forces were computed in a stationary model.

High Frequency Characteristics of Water-Tree Degraded XLPE Insulation in Power Cables

Abstract: The high frequency characteristics, the complex permittivity in particular, of water- tree degraded XLPE insulation in power cables are determined using a two port measurement method. The insulation samples are obtained from both laboratory made samples and those from ex-service cables. The electrical measurements are related to the water tree content of the samples which is estimated by an optical method. An effective materials model is derived to help understand the observed characteristics. From the model it is possible to estimate the water content of the water tree and the conductivity of the water. There is a considerable difference in the water tree characteristics between laboratory and service aged cables. The conductivity of the water in the water trees of service aged cables is much higher than that found in laboratory aged samples.

Detection of lineaments using airborne laser scanning technology: Laxemar-Simpevarp, Sweden

Abstract: The Swedish power industry has been generating electricity by means of nuclear power, and the company Svensk Karnbranslehantering AB (Swedish Nuclear Fuel and Waste Management Co., SKB) manages and disposes of the resulting nuclear waste. SKB’s reference method for disposal involves deposition in a repository at approximately 400–700 metres below ground level (m bgl) in crystalline bedrock. In 2002, site investigations commenced in two municipalities, with the intention of selecting a site for future waste disposal. One of these municipalities is Oskarshamn where the Laxemar-Simpevarp area is located (Fig. 1). In the crystalline bedrock of Sweden, the groundwater flow is almost exclusively restricted to the existing fractures. Hydraulic pathways occur in single fractures in the intact rock, but more extensively in regions of multiple fractures, in “deformation zones”. Many of the deformation zones in the Laxemar-Simpevarp area contain several generations of fractures and may control a major part of the groundwater flow. Light detection and ranging (LIDAR) is a scanning and ranging laser system which determines the distance to the terrain or the target from the instrument (Kraus and Pfeifer 1998; Pfeifer and Briese 2001). Using the data from LIDAR, these deformations zones are frequently manifested as linear escarpments, down to the scale of an individual fracture. However, for the investigated area this effect is occasionally masked, mainly in troughs in the bedrock, by a cover of lateand postglacial reworked deposits. The rock itself has generally only suffered from minor superficial weathering phenomena. Descriptive models are being devised for geology, groundwater flow and biosphere at each site, to assess the long-term safety of the deep repository. The descriptive model of the geology constitutes the basis for SKB’s site descriptive hydrogeological model; of primary interest are large deformation zones, which are defined in space. Some local minor deformation zones will be defined in space (increasingly so as the investigations proceeds), but most of them will be considered as stochastic distributions within the modelled volume together with single fractures (SKB 2004).

Modification of spillways for higher discharge Capacity

Abstract: In Sweden, many dams are to be refurbished in light of the new dam-safety guidelines that lead to higher design floods. To modify the spillway of a dam is often one of the alternatives proposed to increase its discharge capacity. Spillway rebuilding proposals for Ajaure, Bergeforsen, Midskog and Stenkullafors have been examined in hydraulic models. This paper deals with modification of the bottom outlet at Ajaure and proposed crest lowering at the other three overflow spillways. The hydraulic characteristics after the modifications are summarized and compared with the existing situation. The results are shown mainly in terms of water stage—discharge relationship and discharge coefficient, reasons for discrepancy are discussed and explained for each case.

On Co-generation Strategies in the Cities of North-Eastern Europe

Abstract: The high potential for utilization of co-generation power plants in the cities of North-Eastern Europe is illustrated in this paper. The features associated with climatic and economic factors are analyzed. The paper describes the methods for demand forecasting used in the case study and the chosen criteria and methods for economic assessment of different energy supply alternatives. The results of economic assessment support the decision about the optimal placement and parameters of CHPs, including small scale CHPs. Application of cooperative Game theory in order to support the decision-making in the market environment is described and demonstrated on the real life case study.

Organisational factors and nuclear safety - Issues to address in research and development

Abstract: The influence of organisational factors on nuclear safety has been identified in several studies. In spite of their importance no integrated approach to address them seems to have emerged. The paper starts with issues identified in the LearnSafe project to discuss how they have been addressed in research and development within Finland and Sweden and discussed their importance in a larger frame. This discussion is used to suggest a research agenda for what could be called a midfield approach, where utility and regulatory needs could be combined. The paper serves at an introduction to the discussion part of the special session on Organisational learning and learning organisations - the LearnSafe project three years after.

Development of a safety climate questionnaire for nuclear power plants

Abstract: The present work describes the development of a safety climate questionnaire adapted for nuclear power installations. The survey was administered to all personnel at a Swedish nuclear power plant. Exploratory factor analysis revealed 8 factors together explaining 62% of the variance. The first factor was interpreted as Safety management and explained 38% of the variance. The other factors were labelled; Safety knowledge, Resources (time, personnel), Management/change management, Small group climate, Contractors, Documentation/experience feedback, and Occupational safety. The results are discussed and related to theoretical and methodological issues in safety culture and safety climate research.

Management systems and safety culture; reflections and suggestions for research

Abstract: Management systems can be seen as the software of an organisation. Present views on managements systems have emerged from several sources and have now been integrated into the guiding documents produced by IAEA. A discussion of the new documents has in Sweden been initiated within the Vattenfall Nordic Production Safety Management Institute (NSMI), which recently has been established to support the production units in Sweden. The paper starts with a brief description of NSMI and its main tasks. Management systems are then discussed in more detail to suggest research needs within management systems and safety managements. A conclusion of the paper is that a better understanding of the structure and management systems is needed to remove present difficulties in the application of management systems at the nuclear power plants.

Thermally induced convective movements in a standard experimental model for characterization of lesions prior to radiofrequency functional neurosurgery.

Abstract: Experimental exploration of equipment for stereotactic functional neurosurgery based on heating induced by radio-frequency current is most often carried out prior to surgery in order to secure a correct function of the equipment. The experiments are normally conducted in all experimental model including an albumin solution in which the treatment electrode is submerged, followed by a heating session during which a protein clot is generated around the electrode tip. The clot is believed to reflect the lesion generated in the brain during treatment. It is thereby presupposed that both the thermal and electric properties of the model are similar to brain tissue. This study investigates the presence of convective movements in the albumin solution using laser Doppler velocimetry. The result clearly shows that convective movements that depend on the time dependent heating characteristics of the equipment arise in the solution upon heating. The convective movements detected show a clear discrepancy compared with the in vivo situation that the experimental model tries to mimic; both the velocity (maximum velocity of about 5 mm/s) and mass flux are greater in this experimental setting. Furthermore the flow geometry is completely different since only a small fraction of the tissue surrounding the electrode in vivo consists of moving blood, whereas the entire surrounding given by the albumin solution in the experimental model is moving. Earlier investigations by our group (Eriksson et al., 1999, Med. Biol. Eng. Comput. 37, pp. 737-741; Wren, 2001, Ph.D. thesis; and Wren et al., 2001, Med. Biol. Eng. Commit. 39, pp. 255-262) indicate that the heat flux is an essential parameter for the lesion growth and filial size, and that presence of convective movements in the model might substantially increase the heat flux. Thus, convective movements of the magnitude presented here will very likely underestimate the size of the brain lesion, a finding that definitely should be taken into consideration when using the model prior to patient treatment.

Organic soil production involves utilizing lignite xylitol, preferably pure fiber xylitol made of young-tertiary soft lignite, where pure or litter contains dung

Abstract: Organic soil production involves utilizing lignite xylitol, preferably pure fiber xylitol made of young-tertiary soft lignite. 50 wt.% of pure or litter containing dung, preferably in mass ratio of 70:30-90:10 is also used. Transformation is carried out by continuous intensive pressure and shear stress in damp environment conditions. Strongly decomposed, homogeneous of miscellaneous items, and physical and chemical reactions stabilized product is obtained.

Soft brown coal drying method for e.g. heating boiler plants, involves disintegrating brown coals with water contents by crushing coals into grain size until exceeding surface-wet conditions of coals by intensive pressure

Abstract: The method involves disintegrating soft brown coals with water contents by crushing the soft brown coals into grain size until exceeding surface-wet conditions of the brown coals by intensive pressure and/or shear stress or by dynamic stress and/or friction stress. The soft brown coals are dried by a steam-heated pipe dryer and smaller portions of airborne dust are separated from vapors of the pipe dryer. The dried coals are treated to increase hardness and very low dust characteristics.