MIXED CORE SUBCHANNEL MODEL FOR SUBCAL AND COUPLING WITH ANDREA

This paper presents the results of an analysis of flow distribution in VVER-1000 mixed core consisting of fuel assemblies with non-identical spacing grids. The calculation was carried out using the modified subchannel code SUBCAL-AZ which allows to calculate 3D thermal-hydraulic characteristics of the coolant flow in the full core subchannel model coupled with the neutron-physical code ANDREA. This full core subchannel model was created in three variants depending on the ANDREA calculations. The first variant (homogeneous core) consisted of 163 hydraulically identical fuel assemblies TVSA-T mod.2, whereas the other variants (mixed cores) consisted of fuel assemblies TVSA-T mod.0, mod.1 and mod.2. These fuel assemblies mainly differ in types, number and axial coordinate of spacing grids and also in diameter of guide tubes. The influence of mixed core to flow distribution was obtained by comparing these variants

POST CRITICAL HEAT TRANSFER AND FUEL CLADDING OXIDATION

The knowledge of heat transfer coefficient in the post critical heat flux region in nuclear reactor safety is very important. Although the nuclear reactors normally operate at conditions where critical heat flux (CHF) is not reached, accidents where dryout occur are possible. Most serious postulated accidents are a loss of coolant accident or reactivity initiated accident which can lead to CHF or post CHF conditions and possible disruption of core integrity. Moreover, this is also influenced by an oxide layer on the cladding surface. The paper deals with the study of mathematical models and correlations used for heat transfer calculation, especially in post dryout region, and fuel cladding oxidation kinetics of currently operated nuclear reactors. The study is focused on increasing of accuracy and reliability of safety limit calculations (e.g. DNBR or fuel cladding temperature). The paper presents coupled code which was developed for the solution of forced convection flow in heated channel and oxidation of fuel cladding. The code is capable of calculating temperature distribution in the coolant, cladding and fuel and also the thickness of an oxide layer

HEAT TRANSFER MODELLING OF TWO-PHASE FLOW IN ISOLATED CHANNEL

This paper deals with Post-CHF (critical heat flux) heat transfer with the focus on different regimes of film boiling. The new thermal-hydraulic code TUBE 2.0 is presented. This code uses the equation of energy conservation and predefined correlations to establish wall temperature, the departure of nucleate boiling ratio as well as other parameters of cooling in a simple geometry - an isolated channel. With experimental data of inverted annular film boiling from Stewart, the best-performing correlation for calculation of post-CHF heat transfer in the channel was determined. Finally, the new presented code TUBE 2.0 and subchannel code SUBCAL owned by Chemcomex a.s. are compared using results of various experiments conducted by Becker. Data from Stewart could not be used because of inability to predict the onset of boiling crisis with several correlations

MIXED CORE SUBCHANNEL MODEL FOR SUBCAL AND COUPLING WITH ANDREA

This paper presents the results of an analysis of flow distribution in VVER-1000 mixed core consisting of fuel assemblies with non-identical spacing grids. The calculation was carried out using the modified subchannel code SUBCAL-AZ which allows to calculate 3D thermal-hydraulic characteristics of the coolant flow in the full core subchannel model coupled with the neutron-physical code ANDREA. This full core subchannel model was created in three variants depending on the ANDREA calculations. The first variant (homogeneous core) consisted of 163 hydraulically identical fuel assemblies TVSA-T mod.2, whereas the other variants (mixed cores) consisted of fuel assemblies TVSA-T mod.0, mod.1 and mod.2. These fuel assemblies mainly differ in types, number and axial coordinate of spacing grids and also in diameter of guide tubes. The influence of mixed core to flow distribution was obtained by comparing these variants

Activity of the Czech consolidation agency

Práce pojednává o České konsolidační agentuře, důvodech jejího vzniku. Rozebírá činnosti České konsolidační agentury, které řeší proces navrácení nebonitních aktiv do ekonomiky: restrukturalizace vybraných společností a nákup, prodej a správa pohledávek.Dokončená práce s úspěšnou obhajobo

Influence of central tube on mean outlet coolant temperature of central subchannels

katedra jaderných reaktor

Bonds as a source of enterprise funding

V práci jsou představeny dluhopisy z pohledu emitenta jako možný zdroj financování podniku. Je zde popsán proces emise dluhopisů. Podrobněji jsou zkoumány dluhopisy společnosti Škoda Auto, a. s., uvedeny odhady nákladů vydání emise dluhopisů a životnosti emise dluhopisů. Na závěr je popsán a zhodnocen trh s podnikovými dluhopisy v České republice.Ústav ekonomiky a managementuDokončená práce s úspěšnou obhajobo

HEAT TRANSFER MODELLING OF TWO-PHASE FLOW IN ISOLATED CHANNEL

This paper deals with Post-CHF (critical heat flux) heat transfer with the focus on different regimes of film boiling. The new thermal-hydraulic code TUBE 2.0 is presented. This code uses the equation of energy conservation and predefined correlations to establish wall temperature, the departure of nucleate boiling ratio as well as other parameters of cooling in a simple geometry - an isolated channel. With experimental data of inverted annular film boiling from Stewart, the best-performing correlation for calculation of post-CHF heat transfer in the channel was determined. Finally, the new presented code TUBE 2.0 and subchannel code SUBCAL owned by Chemcomex a.s. are compared using results of various experiments conducted by Becker. Data from Stewart could not be used because of inability to predict the onset of boiling crisis with several correlations

Příprava (001) preferenčně orientovaných titanových tenkých vrstev metodou iontového naprašování na termální oxid křemičitý

We propose the ion-beam sputtering deposition providing Ti thin films of desired crystallographic orientation and smooth surface morphology not obtainable with conventional deposition techniques such as magnetron sputtering and vacuum evaporation. The sputtering was provided by argon broad ion beams generated by a Kaufman ion-beam source. In order to achieve the optimal properties of thin film, we investigated the Ti thin films deposited on an amorphous thermal silicon dioxide using X-ray diffraction, and atomic force microscopy. We have optimized deposition conditions for growing of thin films with the only (001) preferential orientation of film crystallites, and achieved ultra-low surface roughness of 0.55 nm. The deposited films have been found to be stable upon annealing up to 300 °C which is often essential for envisaging subsequent deposition of piezoelectric AlN thin films.Práce se zabývá iontovým naprašováním titanových tenkých vrstev a studiem jejich krystalografie a drsnosti. Tyto parametry obvykle nejsou proveditelné konvenčními metodami magnetronového naprašování nebo vakuového napařování. Naprašování bylo realizováno pomocí Kaufmanova iontové zdroje. Nadeponované tenké vrstvy byly analyzovány pomocí XRD a AFM. Optimalizováním depozičních parametrů bylo dosaženo (001) preferenčně orientovaných krystalitů a velmi nízké drsnosti 0,55 nm. Teplotní stabilita titanových tenkých vrstev byla ověřena do 300 °C pro případné depozice nitridu hliníku, který pro dosažení požadovaných vlastností vyžaduje zahřívání substrátu při depozici