Approach and Development of Effective Models for Simulation of Thermal Stratification and Mixing Induced by Steam Injection into a Large Pool of Water

Abstract

Steam venting and condensation in a large pool of water can lead to either thermal stratification or thermal mixing. In a pressure suppression pool (PSP) of a boiling water reactor (BWR), consistent thermal mixing maximizes the capacity of the pool while the development of thermal stratification can reduce the steam condensation capacity of the pool which in turn can lead to pressure increase in the containment and thereafter the consequences can be severe. Advanced modeling and simulation of direct contact condensation in large systems remain a challenge as evident in commercial and research codes mainly due to small time-steps necessary to resolve contact condensation in long transients. In this work, effective models, namely, the effective heat source (EHS) and effective momentum source (EMS) models, are proposed to model and simulate thermal stratification and mixing during a steam injection into a large pool of water. Specifically, the EHS/EMS models are developed for steam injection through a single vertical pipe submerged in a pool under two condensation regimes: complete condensation inside the pipe and chugging. These models are computationally efficient since small scale behaviors are not resolved but their integral effect on the large scale flow structure in the pool is taken into account.

Analysis of thermal stratified storage tank

“…For the model presented in Fig. 4b, 1 774 510 finite elements were applied (152 951 three-node triangular elements, 245 000 four-node square elements as well as 53 690 and 1 888 boundary and apex elements) [5].…”

Validation of Effective Models for Simulation of Thermal Stratification and Mixing Induced by Steam Injection into a Large Pool of Water

“…The effective momentum can be calculated based on the synthetic jet theory which relates the thrust velocity to the frequency and amplitude of water-level oscillation inside the blowdown pipe (see [12,13] for more details). In the POOLEX facility, only three thermocouples are installed inside the blowdown pipe which can be used to determine the water level during a test.…”

“…In [12,13], two effective models, namely, Effective Heat Source (EHS) and Effective Momentum Source (EMS) models, have been proposed and discussed in detail. These models can be utilized to predict thermal stratification or mixing during steam injection into a large pool of water.…”

“…Different regimes of steam condensation in the pool [15] result in different dynamics of the free surface oscillations. It was proposed [12,13] to use "synthetic jet" model [16] in order to predict effective momentum generated by the oscillations of steam-water interface. Specifically, for a single harmonic oscillation, the velocity scale based on the momentum flux [17] is given as…”

Experimental study on steam chugging phenomenon in a vertical sparger

“…The relationship between amplitude and frequency has been analysed using different approaches. The momentum source has been used to relate the amplitude and frequency of oscillations in the pipe to a synthetic jet analogy [22] and to the Richardson number, used then to determine the occurrence of thermal stratification [23]. Villanueva et al [24] identified the Froude…”