G5 Doctoral dissertation (article)

Quantification of Large Steam Bubble Oscillations and Chugging Using Image Analysis

Publication Details
Authors: Hujala Elina
Publishing place: Lappeenranta
Publication year: 2019
Language: English
Related Journal or Series Information: Acta Universitatis Lappeenrantaensis
ISBN: 978-952-335-424-1
eISBN: 978-952-335-425-8
ISSN: 1456-4491
JUFO-Level of this publication:
Permanent website address: http://urn.fi/URN:ISBN:978-952-335-425-8
Location of the parallel saved publication: http://urn.fi/URN:ISBN:978-952-335-425-8


The pressure suppression pool of a boiling water reactor as a safety
system has vital importance from the nuclear reactor safety point of
view. If a loss-of-coolant accident occurs, a large amount of steam is
pushed through the blowdown pipes to the suppression pool. Rapid
condensation of steam causes high dynamic loads on the suppression pool
structures and demands a great deal of its strength. These loads should
be recognized and avoided.

A pattern recognition based image analysis algorithm for vertical
vent pipes was designed and developed in this study. The direct contact
condensation experiment (DCC-05) of the PPOOLEX test facility was used
as a reference test. The algorithm consists of three parts:
pre-processing, where all image processing takes place, pattern
recognition, where the edges of the bubbles are detected, and
postprocessing part, where all images are analysed and data collected.
The algorithm evaluates basic properties of large steam bubbles, such as
volume, surface area, surface velocity and acceleration, and different

Frequency analysis was also conducted on the DCC-05 case. The
analysis showed two main frequencies 53 Hz and 126 Hz. The algorithm was
also applied to computational fluid dynamics (CFD) simulations, where
the algorithm was used to determine critical wavelengths of condensation
driven Rayleigh-Taylor instability in succession to establish the most
suitable grid density for the simulations. A frequency analysis was also
performed for the CFD simulation cases and compared to the results of
the algorithm.

The algorithm was extended to cover cases where multiple bubbles
travel at the same time in the frame being analysed. The extended
algorithm tracks multiple bubble properties in the same image. The
evaluation of surface velocities and acceleration were also improved.

The algorithms work well in evaluating volume, surface area,
velocities and accelerations of large steam bubbles. The research
verified that even from moderate quality video material, it is possible
to acquire high quality quantitative data, if the frame rate of video
had been high enough and the most obtrusive objects could be filtered
out from it as well. The algorithms can help to understand phenomena
that underlay the design of boiling water reactor (BWR) safety systems.

Last updated on 2020-20-03 at 10:03