atw 2018-09v3

atw Vol. 63 (2018) | Issue 8/9 ı August/September
472
AMNT 2018 | YOUNG SCIENTISTS' WORKSHOP
| | Fig. 8.
Time resolved washed off mass for different wash-off coefficients.
Parameters according to Table 1 and ρ p = 5000 kg/m 2 .
transport simulations last for 30 s.
First the influence of the Weber
number is investigated, see Figure 6.
Increasing Weber numbers correspond
to larger water velocities and
an increasing percentage of wetted
surface. Consequently for larger
Weber numbers more particle mass is
washed off. Thus two effects manifest
in the results: first the larger velocities
are able to wash-off even particles
with larger density. And secondly the
enlarged percentage of wetted surface
enhances the particle wash-off, since
much more particles can be eroded
by the water.
Figure 7 shows the variation of the
particle density. Particles with larger
density cannot be eroded that easily
and hence the total washed off mass
decreases with increasing particle
density, as expected. In Figure 8 the
influence of the wash-off coefficient is
investigated. The total washed off
mass, which is to a large extent determined
by the area of wetted surface,
does not change with different values
of ~ r e but the temporal behavior does.
For a large value of ~ r e a large fraction
of particles erodes in a short timespan.
Asymptotically for t → ∞ the
total washed off mass converges
always to the same amount.
In order to compare the simulations
with experimental data a parameter
set based on Weber et. al [1]
is chosen. Figure 9 displays the results
of the simulation and the experimental
data of test 4. In the experiments
the particles are collected in intervals
of 10 s for a total duration of 130 s.
Due to this sampling strategy the time
resolved washed off particle mass in
the simulations is presented in the
same manner and for the same
duration. A good agreement for the
temporal course of the wash-off as
well as for the total washed off mass
can be achieved.
7 Conclusions and
discussion
This paper presents a CFD particle
wash-off model and particle transport
by gravity driven flows. A parameter
variation was conducted within the
setting of a simplified geometry and
with the geometry of the laboratory
tests. The particle wash-off model,
which is based on Shields criterion
[12] and Weber et. al [1], shows the
expected behavior for varying particle
properties such as particle density and
wash-off coefficient. One key influencing
parameter for the resulting
washed off mass is the percentage of
area covered by water in each case,
which differs with inclination and
mass flow rate. First simulations
with the laboratory geometry show
satisfactory agreement when compared
to the experiments. Nevertheless,
the prediction of particle
wash-off for a large variety of setups
as in the laboratory experiments
( different inclinations, particle and
surface properties and initial loadings)
remains a great challenge and
further comparisons for different
parameter sets are current work in
progress. This study contributes to
the development of a semi-empirical
model to quantify the aerosol washoff
and the wetted surface area during
an accident in a light water reactor.
Acknowledgment
The project underlying this report
is funded by the German Federal
Ministry of Economic Affairs and
Energy under grant number 1501519
on the basis of a decision by the
German Bundestag. The THAI project
was carried out on behalf of the
Federal Ministry for Economic Affairs
and Energy under grant number
1501455 on the basis of a decision by
the German Bundestag. We are also
grateful for the support from Becker
Technologies and the GRS.
References
| | Fig. 9.
Comparison of test 4 of the laboratory experiments with the simulations of particle wash-off
with inclination α = 20°, mass flow rate m = 11 g/s, initial loading c s = 12.5 g/m 2 ,
particle diameter d p = 2 μm, particle density ρ p = 5000 kg/m 3 and wash-off coefficient ~ r e = 0.025 s –1 .
[1] G. Weber, F. Funke, W. Klein-Hessling,
and S. Gupta. Iodine and silver washdown
modelling in COCOSYS-AIM by
use of THAI results. Proceedings of the
International OECD-NEA/NUGENIA-
SARNET Workshop on the Progress in
Iodine Behaviour for NPP Accident
Analysis and Management, 2015.
[2] S. Gupta, F. Funke, G. Langrock, G.
Weber, B. von Laufenberg, E. Schmidt,
M. Freitag, and G. Poss. THAI Experiments
on Volatility, Distribution and
Transport Behaviour of Iodine and
Fission Products in the Containment.
Proceedings of the International
OECD-NEA/NUGENIA-SARNET Workshop
on the Progress in Iodine
Behaviour for NPP Accident Analysis
and Management, p. 1-4, 2015.
[3] M. Freitag, B. von Laufenberg, M.
Colombet, K. Amend, and M. Klein.
Particulate fission product wash-down
from containment walls and installation
surfaces. Proceedings of the 47 th
Annual Meeting on Nuclear
Technology, Hamburg, 2016.
AMNT 2018 | Young Scientists' Workshop
Development and Validation of a CFD Wash-Off Model for Fission Products on Containment Walls ı Katharina Amend and Markus Klein