atw 2018-09v3

inforum

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

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