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NKS Programme Area:NKS-R
Research Area:Thermal Hydraulics
Report Number:NKS-316
Report Title:Effective Models for Simulation of Thermal Stratification and Mixing Induced by Steam Injection into a Large Pool of Water
Activity Acronym:ENPOOL
Authors:Hua Li, Walter Villanueva, Pavel Kudinov,
Abstract:Steam condensation in a large pool of water creates both a source of heat and a source of momentum. Complex interplay between these two sources leads to either thermal stratification or mixing. Development of thermal stratification in a pressure suppression pool (PSP) of a boiling water reactor (BWR), increases temperature of the free surface reducing the steam condensation capacity of the pool and increasing containment pressure. It is important to know how fast a stratified pool can be mixed. Modelling of direct contact condensation on the steam-water interface remains a computational challenge. Therefore Effective Heat Source (EHS) and Effective Momentum Source (EMS) models have been proposed to model thermal stratification and mixing in case of steam injection through a vertical pipe submerged in a pool under two condensation regimes: complete condensation inside the pipe and chugging. Computational efficiency and sufficiently accuracy of the models are achieved by resolving only integral effect of small scale steam condensation phenomena on the large scale flow structures and temperature distributions in the pool. The models are implemented in GOTHIC® software. In previous NKS reports, validation of EHS and EMS models against POOLEX STB and PPOOLEX STR tests have been presented. In this report, we focus on the validation of the EHS/EMS models against recent PPOOLEX MIX tests. Excellent agreement in the development of thermal stratification and mixing in the pool between the experiment and simulation has been achieved. For completeness, an updated discussion of some of the previous STB and STR tests have been included with parametric sensitivity analysis. Improvement of EHS/EMS models are discussed. Effective momentum can be determined based on the frequency and amplitude of oscillations in the blwodown pipe. We demonstrate that existing analytical models (e.g. by Nariai) that can be used for prediction of the frequency and amplitude were developed using data from small scale experiments and have rather large uncertainty when applied to large scale PPOOLEX tests. A scaling approach is proposed to generalize available data on amplitude and frequency of oscillations during chugging at different scales.
Keywords:Thermal Stratification, Mixing, Pressure Suppression Pool, Containment, Thermal Hydraulic, GOTHIC, Light Water Reactor
Publication date:27 Oct 2014
ISBN:ISBN 978-87-7893-395-9
Number of downloads:1002
Download:pdf NKS-316.pdf

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