atw - International Journal for Nuclear Power | 04.2023

atw Vol. 68 (2023) | Ausgabe 4 ı Juni
Experimental Investigation on the
Pool Scrubbing Behaviour of soluble
and mixed Aerosol Components
René Vennemann, Michael Klauck, Tobias Jankowski, Hans-Josef Allelein, Marco K. Koch
Introduction
The retention of aerosol particles and especially of fission products in liquid pools, also known as pool
scrubbing, is an employed process in the frame of postulated severe accident scenarios in nuclear power
plants. In case of a boiling water reactor (BWR), the reactor pressure vessel (RPV) is equipped with Safety
Relief Valves (SRVs), that might reduce undesirable pressure increases in the RPV by gas release into the
suppression pool and thereby maintaining the cooling circuits’ integrity. In case of a postulated severe accident
scenario, the suppression pool has the function to condensate steam from the gas flow and to scrub
fission products from the gas flow before it is released to the containment atmosphere. Beside this scenario
Gupta et al. [GUP23] describe more postulated accident scenarios where pool scrubbing phenomena can be
expected, for example in a steam generator tube rupture scenario or as part of a filtered containment venting
system. The focus of this work is to expand the experimental database on pool scrubbing and to discuss the
aerosol retention for individual size classes. Most experiments available in the open literature are carried
out with insoluble particles like SnO 2 [HER18, REH22] . Consequently, this work focusses on the retention of the
soluble CsI and a mixture of CsI and SnO 2 to enhance the knowledge on the behaviour of aerosols typical
for postulated severe accident scenarios
RESEARCH AUS DEN AND UNTERNEHMEN
INNOVATION 71
SAAB test facility
The SAAB test facility is shown in figure
1 [ALL18] . The test vessel has a modular
design; thus the pool height can be varied
from 2.25 m to 6.25 m and the distance to
the measuring device at the outlet can be
kept almost identical. Due to five identical
one-meter-high segments the test vessels’
total height can be changed while the gas
space above the pool is kept at a constant
volume. In addition to the five identical
parts the vessel has a bottom segment
with a gas inlet and a conical top part
with openings for measurement devices.
The inner diameter of the test vessel is
1.5 m, and the maximum possible water
volume is 10 m³. The injection nozzle is situated
0.75 m above the vessels’ floor and
is upward directed. The inner diameter of
the nozzle outlet is 0.021 m. Aerosols are
generated with a spraying system (soluble
particles) and with a particle disperser
with brush (insoluble particles) [ALL20] and
afterwards fed into a mixing chamber,
where they are conditioned and blended.
During this process additional carrier gas
and steam can be added. Once the aerosol
passed the mixing chamber it is measured
with an Electrical Low-Pressure Impactor
(ELPI+) from Dekati, which determines
| Fig. 1
SAAB test vessel [ALL18].
the aerosol concentration for fourteen
size classes, and is injected into
the water pool of the vessel. After
passing the water pool, the aerosol is
measured by a second ELPI+ system,
located 0.625 m above the pool surface
in the conical part of the vessel.
Experiment
A pool height of 2.25 m up to 6.25
m is realized, i.e. the submergence
of the injection nozzle is 1.5 m up to
5.5 m. Nitrogen is used as carrier gas
and is injected with 20 m³/h (5.56 x
10 –3 m³/s) up to 80 m³/h (2.22 x 10 –2
m³/s). Thus, the Weber number is
approximately 5 x 10 4 – 8 x 10 5 . The
tests are performed with an ambient
pool temperature (approximately
22 °C) and with caesium iodine
(CsI) or a mixed aerosol consisting
of 60 mass percentage CsI and 40
mass percentage tin dioxide (SnO 2 ).
As in previous tests [VEN22] the inlet
gas temperature is 30 °C and to keep
the humidity on a constant level, the
sampling temperature of the ELPI+
is at 60 °C. The experiment was repeated
more than once, to obtain
reliable measurement results.
Research and Innovation
Experimental Investigation on the Pool Scrubbing Behaviour of soluble and mixed Aerosol Components ı René Vennemann, Michael Klauck, Tobias Jankowski, Hans-Josef Aus den Allelein, Unternehmen
Marco K. Koch