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1

Impact of local property variations of reactor coolant on cladding temperature distribution in supercritical water reactors

Zhong J., Antal S. P., Podowski M. Z.

Journal of Power Technologies

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2014

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Vol. 94, nr 5

51--60

EN

Fluids at supercritical pressures are considered to be very promising as coolants for Generation IV reactor systems, including the supercritical water cooled reactor (SCWR), the CO2-cooled reactor (SCCO2R) and the Brayton cycle as a secondary system in sodium-cooled fast reactors. The operating conditions of such reactors allow for a significant thermodynamic efficiency increase of the respective power plants. On the other hand, several unresolved issues must still be addressed in order to develop a viable design of supercritical fluid nuclear systems. Examples include: in-core heat transfer in SCWRs, heat exchangers in the S-CO2 Brayton cycle, and flows in complex geometries of SCO2 compressors. It has been shown before that the understanding of the effect of fluid property variations on turbulence is a major factor in our ability to predict the combined fluid mechanics and heat convection in systems and components using supercritical fluids. The objective of this paper is to present the results of analysis on the effect of local multidimensional flow and heat transfer phenomena on the temperature distribution inside future SCWRs. Two proposed SCWR designs have been considered: a single-pass and a two-pass coolant flow configurations through the reactor core. It should be noted that a preliminary documentation of the results of the current work has been included in the materials of the NURETH-15 conference.

2

On the modelling of multidimensional two-phase flows

Anglart H., Podowski M. Z.

Zeszyty Naukowe Politechniki Świętokrzyskiej. Mechanika

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1999

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Z. 67

153--162

EN

One of the current challenges in modelling of two-phase flows is the ability to predict the detailed spatial distribution of phases in complex geometries. The phase distribution in a fuel assembly of a nuclear reactor is the key parameter, which determines the reactor safety and performance. In particular, such limiting phenomena as the Critical Heat Flux or the onset of two-phase flow instability can not be predicted with the required accuracy if the detailed phase distribution in the fuel assembly is not known. The purpose of this work is to present a mechanistic multi-field model for the prediction of two-phase flows in an arbitrary channel. The averaged conservation equations and proper closure relationships for interfacial terms are shown. The model is applied for the prediction of phase distribution in bubbly and slug flows in pipes and between two parallel walls, where most experimental data exist. The numerical results were compared against experimental data and good agreement has been obtained.

3

On the mechanistic modeling of forced-convection low-quality boiling

Podowski M. Z.

Zeszyty Naukowe Politechniki Świętokrzyskiej. Mechanika

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1999

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Z. 67

97--111

EN

Practical applications of forced-convection boiling encompass a wide spectrum of industrial systems, including but not limited to, thermal energy generation systems, because of the complexity of phenomena governing boiling heat transfer in general, and subcooled boiling in particular, a commonly used approach to both fundamental and practical problems has traditionally been based on experimental correlations rather than mechanistic models. The recent progress in computational fluid dynamics (CFD), combined with improved experimental techniques in two-phase flow and heat transfer, makes the use of rigorous physically-based models a realistic alternative to the simplistic phenomenological approach which dominated the field in the past. The objective of this paper is to discuss some of the recent accomplishments in the mechanistic modeling of forced-convection low-quality boiling, including both the nucleate boiling regime and the mechanisms governing the departure from nucleate boiling (critical heat flux - CHF).