Modellierung des unterkühlten Siedens in ATHLET und Anwendung in wassergekühlten Forschungsreaktoren

For the analysis of leaks and transients in Power reactors, the thermohydraulics code ATHLET has been developed at the GRS. In order to extend the application area of this code to the safety analysis of research reactors, a rnodel is implemented to describe the thermodynarnic nonequilibriurn effects in subcooled boiling regime. The aim is to simulate void distribution and thermodynamric instability, which is practicularly pronounced in research reactors due to high power densities and low system pressures, and to include the influence of the steam formed in this boiling regime on the neutron balance. The model developed as part of this work considers the competing effects of vaporization and condensation during subcooled boiling. lt describes the rate of bubble generation on superheated surfaces and the subsequent condensation of steam in the subcooled liquid. The installed model is validated by postealculations of two extensive series of experiments. In the first series, the McMaster experiments on axial void distribution in the subcooled boiling regime are recalculated. The postcalculations show that the extented program is capable of caculating the axial void distribution in the subcooled boiling regime with a maximum deviation of approx. 23% from the experiment. The second seriesconcern KFA experiment on thermohydraulic instability during subcooled boiling, which cover a wide parameter range of heat flux density, inlet temperature and channel width. The postcalculations of this experimental series show that the simulation of thermohydraulic instability is ensured by the program extension. The point of beginning instability is conservatively determined in 20 of a total of 27 recaleulated experiments. The extended and verified program is finally used to simulate the Jülich research reactor FRJ-2. For this purpose, a full-scale simulation model of the entire plant is developed ensuring, in particular, a precise reproduction of the geometry and the arrangement of the annular fuel element cooling channels. The modelled reactor plant is first used to simulate normal reactor operation. The resulting steady-state temperature and pressure distributions assuming a thermal power of 23 MW show good agreement with real operating data. Finally, safety investigations are conducted to examine plant behaviour under designbasis accident conditions. This includes failure of all three rnain coolent pumps with proper and delayed reactor scram. In both cases, the simulation shows that the fuel elements are not endangered in any phase of the transient, although in the event of adelayed scram initial signs of parallel channel instability due to steam formation in the central fuel element are to be observed which, however, only prevails for a skort period of 30 ms

Formulating an optimal long-term energy supply strategy for Syria using MESSAGE model

An optimal long-term energy supply strategy has been formulated based on minimizing the total system costs for the entire study period 2003-2030. The national energy chain was modelled covering all energy levels and conversion technologies. The results indicate that the primary energy will grow at annual average rate of 4.8% arriving 68 Mtoe in 2030. The total installed electric capacity will be optimally expanded from 6885 to 19500 MW in 2030. Furthermore, to ensure supply security the future national energy system will rely mainly upon oil and natural gas (NG) with limited contribution of renewables and nuclear to the end of study period. The share of NG will increase gradually up to 2020 and then retreat. Owing to the continuous decrease of oil production, oil export is expected to vanish in 2012 and the country will import about 63% of its primary energy demand in 2030. Thus, the expected long-term development of national energy sector indicates a hard challenge for the future national economy. The employing of sensitivity analysis clarifies the importance of wind turbines operation time and discount rate. The analysis proves that nuclear option is insensitive to overnight cost increase up to 85% of the reference case value.Energy supply strategy MESSAGE model Optimal expansion plan

Modellierung des unterkuehlten Siedens in ATHLET und Anwendung in wassergekuehlten Forschungsreaktoren

Es wird ein Modell implementiert, das die Beschreibung der thermodynamischen Ungleichgewichtseffekte beim unterkuehlten Sieden erlaubt. Das Modell beruecksichtigt die beim unterkuehlten Sieden gegenseitig konkurrierenden Verdampfungs- und Kondensationseffekte. Es beschreibt die Dampfblasenerzeugungsrate an den ueberhitzten Heizflaechen sowie die anschliessende Kondensation der Dampfblasen in der unterkuehlten Kernstroemung. Das eingebaute Modell wird durch Nachrechnung von zwei Versuchsreihen validiert. Das erweiterte und in dieser Weise verifizierte Programm ATHLET wird zur Modellierung des Juelicher Forschungsreaktors FRJ-2 eingesetzt. Zu diesem Zweck wird ein umfassendes Abbildungsmodell der Gesamtanlage entwickelt. Besonderes Gewicht wird auf die genaue Nachbildung der Geometrie und der Anordnung der annularen Brennelemente gelegt. Mit der abgebildeten Reaktoranlage wird zuerst der Normalbetrieb des Reaktors simuliert. Die sich einstellenden stationaeren Temperatur- und Druckverteilungen bei einer thermischen Reaktorleistung von 23 MW zeigen gute Uebereinstimmung mit den Betriebsdaten. Schliesslich werden Sicherheitsuntersuchungen durchgefuehrt, um das Verhalten der Anlage bei Auslegungsstoerfaellen zu ueberpruefen. Dazu zaehlt der Ausfall aller drei Hauptkuehlmittelpumpen mit rechtzeitiger und verzoegerter Reaktorabschaltung. In beiden Stoerfaellen zeigt die Simulation, dass die Brennelemente in keiner Phase der Transiente gefaehrdet werden, obwohl beim Stoerfall der verzoegerten Abschaltung infolge Dampfbildung im zentralen Brennelement erste Anzeichen der Parallelkanal-Instabilitaet zu beobachten sind, die allerdings nur fuer eine kurze Zeitspanne von 30 ms andauert. (orig./HP)A model is implemented to describe the thermodynamic nonequilibrium effects in subcooled boiling regime. The aim is to simulate void distribution and thermodynamic instability, which is practicularly pronounced in research reactors due to high power densities and low system pressures, and to include the influence of the steam formed in this boiling regime on the neutron balance. The model developed considers the competing effects of vaporization and condensation during subcooled boiling. It describes the rate of bubble generation on superheated surfaces and the subsequent condensation of steam in the subcooled liquid. The installed model is validated by postcalculations of two extensive series of experiments. The extended and verified program is used to simulate the Juelich research reactor FRJ-2. For this purpose, a full-scale simulation model of the entire plant is developed ensuring, in particular, a precise reproduction of the geometry and the arrangement of the annular fuel element cooling channels. The modelled reactor plant is first used to simulate normal reactor operation. The resulting steady-state temperature and pressure distributions assuming a thermal power of 23 MW show good agreement with real operating data. Safety investigations are conducted to examine plant behaviour under design-basis accident conditions. This includes failure of all three main coolent pumps with proper and delayed reactor scram. In both cases, the simulation shows that the fuel elements are not endangered in any phase of the transient, although in the event of a delayed scram initial signs of parallel channel instability due to steam formation in the central fuel element are to be observed which, however, only prevails for a short period of 30 ms. (orig./HP)SIGLEAvailable from TIB Hannover: RA 831(2961) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Assessment of technology-based options for climate neutrality in Austrian manufacturing industry

The goals set forth by the European Green Deal require extensive preparation and coordination of all stakeholders. As a valuable tool, energy scenarios can generate the necessary information for stakeholders to envision the right steps in preparing this transition. The manufacturing industries represent an especially important sector to investigate. They are responsible for both high energy consumption and GHG emission figures on the one hand side and provide great economic value for member countries on the other. We aim to provide a close investigation of all thirteen industrial subsectors that can be used as a solid information basis both for stakeholders within the manufacturing industries and policymakers. Our approach includes all industrial production processes. We achieve this by considering both transformation processes, such as blast furnaces or industrial power plants, and final energy-application. In addition, both scope 1 and 2 emissions of manufacturing industry are assessed in an effort to transparently indicate the interdependencies of industrial decarbonisation efforts with the overall energy system. We propose the integration of a novel stakeholder-based scenario, that puts special emphasis on first-hand information on mid to long-term planning of key industrial representatives, thereby going beyond existing scenario narratives (e.g., scenarios according to the European Monitoring Mechanism). Thus, a balanced deep decarbonisation scenario using best-available technologies can be compared with existing industry plans. To address these points, we have chosen Austria as a case study. Results indicate that industry stakeholders are in general agreement on their subsector-specific technology deployment and already envision investments towards a low-carbon pathway for their respective subsectors. While today's manufacturing industries rely at large on a great diversity of (mostly fossil) energy carrier supply, deeply decarbonised manufacturing industries of the future may be based on the following main energy carriers; electricity, CO2-neutral gases, and biomass. To mitigate emissions from geogenic sources, carbon capture technologies are needed. On the other hand, the synthesis of olefins in the chemical industry may provide a sink for CO2 assuming long-term use after production. In addition to the option of using it across subsectors, captured CO2 will have to be stored or sold to other economies. Comparison of the developed scenarios allows the identification of no-regret measures to enable climate neutrality by 2050 that should be deployed as soon as possible by push and pull incentives. The model results of the two transition scenarios show the need for technology promotion as well as infrastructure development needs and allow the identification of possible corridors, focal points, and fuel shifts – on the subsector level as well as in energy policy. Among others, the modelled magnitude of renewable energy consumption shows the need for swift expansion of existing national renewable energy potentials and energy infrastructure, especially for energy intensive industry regions. In light of the current energy consumption in other economic sectors (most notably in buildings or transport) and limited renewable potentials, large import shares of national gross domestic energy consumption are likely for Austria in the future

Safety Analysis for Research Reactors

The aim of safety analysis for research reactors is to establish and confirm the design basis for items important to safety using appropriate analytical tools. The design, manufacture, construction and commissioning should be integrated with the safety analysis to ensure that the design intent has been incorporated into the as-built reactor. Safety analysis assesses the performance of the reactor against a broad range of operating conditions, postulated initiating events and other circumstances, in order to obtain a complete understanding of how the reactor is expected to perform in these situations. Safety analysis demonstrates that the reactor can be kept within the safety operating regimes established by the designer and approved by the regulatory body. This analysis can also be used as appropriate in the development of operating procedures, periodic testing and inspection programmes, proposals for modifications and experiments and emergency planning. The IAEA Safety Requirements publication on the Safety of Research Reactors states that the scope of safety analysis is required to include analysis of event sequences and evaluation of the consequences of the postulated initiating events and comparison of the results of the analysis with radiological acceptance criteria and design limits. This Safety Report elaborates on the requirements established in IAEA Safety Standards Series No. NS-R-4 on the Safety of Research Reactors, and the guidance given in IAEA Safety Series No. 35-G1, Safety Assessment of Research Reactors and Preparation of the Safety Analysis Report, providing detailed discussion and examples of related topics. Guidance is given in this report for carrying out safety analyses of research reactors, based on current international good practices. The report covers all the various steps required for a safety analysis; that is, selection of initiating events and acceptance criteria, rules and conventions, types of safety analysis, selection of computational tools and presentation of the results of the analysis. It also discusses various factors that need to be considered to ensure that the safety analysis is of an acceptable quality. In specific terms, the calculations and methods in this report can be used for the safety analysis of newly designed research reactors, modifications and experiments with impact on safety, and upgrades of existing reactors, and can also be used for updating or reassessing previous safety analyses of operating research reactors. This publication will be particularly useful to organizations, safety analysts and reviewers in fulfilling regulatory requirements and recommendations related to the preparation of the safety analysis and its presentation in the safety analysis report. In addition, it will help regulators conduct safety reviews and assessments of the topics covered