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Experimental study of incipient motion and transportation of<br />
particles with various shape<br />
K.J.A. Westin a, F. Alavyoon b and M. Henriksson a<br />
Objects (particles) entering the reactor pressure vessel in a nuclear power plant<br />
may cause damages to the fuel assemblies, with expensive production stops as a<br />
consequence. At present time there are intentions to increase the thermal power in<br />
many plants, which also implies increased flow rates. A question that has received<br />
attention lately is how the increased flow rate will affect the probability for particles<br />
entering the reactor pressure vessel.<br />
The aim of the present study is to quantify the required flow velocity for<br />
transportation of particles with generic shapes (cylinders, washers, sphere). At first the<br />
drag coefficients for free falling particles were determined by measuring the terminal<br />
fall velocity in a test tank. These tests also demonstrated the inherently oscillating<br />
motion that is obtained with the washers and the low-aspect ratio cylinders. The<br />
incipient motion of the particles subjected to a slowly increasing flow rate was then<br />
studied in a horizontal pipe with a dimension similar to a feed water pipe (inner<br />
diameter 290mm). The particle motion in a 90 bend and in a vertical pipe section<br />
was examined in order to determine the required flow rate to obtain a vertical<br />
transportation of the particles, and the particle behaviour near an obstacle was also<br />
studied. Besides video recordings, simultaneous measurements of flow rates and wallshear<br />
stress (Preston tubes) were carried out.<br />
The required flow rates to obtain a transportation of the particles along the vertical<br />
pipe were quantified, showing 1.2 to 5 times larger flow velocity than predicted by<br />
assuming a balance between the drag force (based on mean bulk velocity) and the<br />
gravitational force. It was also shown that the curvature of the pipe had a clear<br />
stabilizing effect on cylinders aligned with the flow, which significantly delayed the<br />
particle transportation along the horizontal pipe.<br />
a<br />
Vattenfall Utveckling AB, SE-814 26 Älvkarleby, Sweden.<br />
b<br />
Forsmarks Kraftgrupp AB, SE-742 03 Östhammar, Sweden.<br />
Figure: (Left) Test particles. (Right) Test rig for transportation tests (acrylic glass).<br />
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