A4 Conference proceedings

Frequency Analysis of Chugging Condensation in Pressure Suppression Pool System with Pattern Recognition

Publication Details
Authors: Hujala Elina, Tanskanen Vesa, Hyvärinen Juhani
Publication year: 2017
Language: English
Related Journal or Series Information: International Topical Meeting On Nuclear Reactor Thermal Hydraulics
Title of parent publication: 17th International Topical Meeting on Nuclear Reactor Thermal Hydraulics
JUFO-Level of this publication: 0
Open Access: Not an Open Access publication


Direct contact condensation (DCC) phenomena in boiling water reactor (BWR) pressure suppression pool
systems need to be understood to properly assess the performance of the pool as a heat sink and as a
safety critical structure. Condensation oscillations in the form of chugging are challenging to predict by
computational fluid dynamics (CFD) methods but safety relevant because of associated high dynamic
loads on in-pool structures and the pool itself. Recently, new measurement methods for CFD validation
purposes have become available. One of these techniques is visual observation using the high speed
cameras and suitable data processing method. Pattern recognition is a well suited technique for the
determination of large oscillating bubble dynamics in a pressure suppression pool.
In this work, the formation and collapse of the steam bubbles in chugging condensation mode are
evaluated by using the pattern recognition algorithm. The pattern recognition algorithm is based on video
material recorded during the direct contact condensation experiment DCC-05 of the PPOOLEX test
facility of Lappeenranta University of Technology (LUT). The formation speed, the shape and size of the
steam bubbles and the acceleration of collapsing bubbles are estimated with the algorithm. Fast Fourier
transform (FFT) is used for frequency analysis of the pattern recognized data. The frequencies found are
compared to the frequency data of the pressure transducers collected during the experiment and to the
previous results of the NEPTUNE_CFD simulations of the same experiment.
The frequency analysis shows that the chugging frequencies of the steam bubbles range from 1 to 3 Hz, as
predicted. Also the natural frequencies of the bubbles are visible around 50 Hz. Another frequency spike
was observed close to the 125 Hz. This frequency is close to the mechanical resonance frequencies of the
suppression pool and the blowdown pipe. Because of neither the pressure suppression pool nor the
blowdown pipe are visible to the pattern recognition, the spike of the higher frequencies is most likely
from the interfacial area of the bubble which resonates with the suppression pool system, affecting rapid
condensation at a certain point.

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Last updated on 2018-23-02 at 09:46