Selection of Appropriate Turbulance Model in Fuel Bundle of Nuclear Energy: In Context With Inter-Subchannel Mixing of Coolant for Single Phase Flow

Selection of Appropriate Turbulance Model in Fuel Bundle of Nuclear Energy: In Context With Inter-Subchannel Mixing of Coolant for Single Phase Flow

Shashi Kant Verma (National Institute of Technology Raipur, India), S. L. Sinha (National Institute of Technology Raipur, India) and D. K. Chandraker (BARC, India)
DOI: 10.4018/978-1-5225-3035-0.ch012
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This chapter presents an overview of various types of turbulence model and their effect on thermal-hydraulic characteristics of nuclear fuel bundle, both past and present using Computational Fluid Dynamic (CFD) approach. It includes the mathematical definition related to fuel bundle in nuclear energy. The various types of geometrical arrangement like Pressurized Water Reactor (PWR), Boiling Water Reactor (BWR), etc., are stressed. The solution procedures that are applicable to the various reactor types are introduced here and presented in detail for different types of turbulence models. Study of these characteristics enables the student to appreciate the effect of the different types of turbulence models on turbulent mixing and related phenomena. Finally, recommendations of turbulence model for rod bundle are finalized. The inclusion of related references provides a starting point for the interested reader / researchers /industrialists.
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The basic mode of operation of the most nuclear reactors is that the coolant flowing through the core of the reactor removes heat produced by nuclear fission and conveys it to a steam generator. The steam drives a turbine coupled to a generator, which produces electricity. Fuel rod bundle is the heart of the nuclear reactor system. Over the precedent 20 years, momentous improvements have been ended in industrial Computational Fluid Dynamics (CFD) codes, in computing supremacy and in parallel-computing. These improvements have facilitated the utilization of CFD as a universal practice in numerous sectors, its use in the nuclear diligence is rising. In industrial computational fluid dynamics codes, there is more than one turbulence model built in. It is the addict accountability to decide one of those models, appropriate for the dilemma considered. Even though considerable progresses completed in the pasture, the use of CFD in predicting single-phase flows in rod bundles tranquil faces a few challenges due to difficulties in precisely predicting the turbulent structures such as Secondary flows, Vortex shedding, and Flow pulsations that donate to inter-channel mixing (Krauss and Meyer, 1996; Baglietto and Ninokata, 2005). The mixing of cooling fluid in rod bundles from one subchannel to another through the gaps between the rods reduces the temperature differences in the coolant as well as beside the perimeter of the rods. The observable fact of natural mixing was earliest intensively investigated in the 1960s and leftovers a theme of research up to the current period. Universal features of these simulations are the computations performed by the researchers by means of k-ε turbulence model. Evaluation of the simulation grades with experimental data was rarely acceptable. Models based on the Reynolds-stress transport equations can offer qualitatively accurate solutions. As a probable justification, secondary flow was deduced from measurements by numerous experimentalists (Trupp and Azad, 1975; Trippe and Weinberg, 1979b; Seale, 1979; Rehme, 1987) and fairly recently its subsistence has been supported by analytical marks (Kim and Kim, 2004). Turbulent mixing is recognized as a transport method which is caused by the lateral velocity variation in the gap among two sub-channels. In this means, mass, momentum or energy can be elated in lateral way. This procedure has a diffusive nature. For the explanation of this method, a diffusion coefficient and a gradient of the transportable flow variable is requisite. Normally, our endeavour is informative, we would identify the reader’s attention to the reality that turbulence models have to be certain based on theoretical considerations and / or enough information obtained from measurements. The significance of this revision can be traced back to the deletion of heat in a reactor. To sustain the reactor at a safe and constant temperature and, at the same time, operate at highest efficiency, the stability and control of the heat elimination is of great significance. The secondary flow and cross-channel flow of water in different geometry promotes the heat deletion in the radial direction. This chapter will concentrate on the analysis of cross-flow in rod-bundle geometry. Although the theoretical and computational approach is very interesting, this learning was solely performed on computational basis. Due to dissimilar profile of the sub-channels, the thermal hydraulic descriptions of the coolant flowing through the sub-assembly are also unlike which requests a thorough and profound understanding.

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