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Second Thermal and Fluids Engineering  Conference

ISSN: 2379-1748
ISBN: 978-1-56700-430-4

TURBULENCE INDUCED THERMAL MIXING EFFECTS AND THERMAL FATIGUE ANALYSIS IN T-JUNCTION CONFIGURATIONS IN PRESSURIZED WATER REACTORS (PWR)

Debashis Basu
Fire Technology Department, Chemistry and Chemical Engineering Division, Southwest Research Institute

Mohammed Hasan
UTC Aerospace Systems

Kaushik Das
Thermal Modeling and Analysis Systems Engineer, The Giant Magellan Telescope Organization

Abstract

In a nuclear reactor, thermal striping, stratification, and cycling take place as a result of mixing of pressurized hot and cold water streams. The fluctuating thermal load generated by such unsteady mixing may result in fatigue damage of the associated structures. Generally, thermal fatigue is considered to be a long-term degradation mechanism in nuclear power plants. This is significant, especially for aging power plants, and improved screening criteria are needed to reduce risks of thermal fatigue and improve methods to determine the potential significance of fatigue. Though fluid mixing and thermal fatigue have been studied separately, a number of issues related to complex interaction between turbulent mixing and the mechanical structure of the Light Water Reactor (LWR) have not yet been resolved. The primary objective of the study reported here was to advance the use of numerical modeling techniques for reactor safety determination by developing a proof-of-concept benchmark simulation that demonstrates that computational methods can be used to address turbulent mixing-induced thermal fatigue in the context of LWR operations. In addition, the structure of turbulence in the T-junction was investigated. A computational method comprised of Large Eddy Simulation (LES) and Unsteady Reynolds Averaged Navier Stokes (URANS) modeling was used to simulate turbulence and capture the coherent structures and turbulence scales. In addition, Conjugate Heat Transfer (CHT) analyses were performed to predict the thermal field and temperature distribution in the solid piping material of the T-junction. Finally, the corresponding thermal stress in the solid pipe was estimated based on a simplified one-dimensional model to assess the thermal-structure degradation. Fatigue calculations show that the initiation of cracking due to thermal fatigue primarily depends on the temperature difference between the hot and cold streams.

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