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|NKS Programme Area:||NKS-R|
|Research Area:||Severe accidents|
|Report Title:||Study on Effective Particle Diameters and Coolability of Particulate Beds Packed with Irregular Multi-size Particles|
|Authors:||Sachin Thakre, Weimin Ma, Pavel Kudinov, Sevostian Bechta, |
|Abstract:||One of the key questions in severe accident research is the coolability of the debris bed, i.e., whether decay heat can be completely removed by the coolant flow into the debris bed. Extensive experimental and analytical work has been done to substantiate the coolability research. Most of the available experimental data is related to the beds packed with single size (mostly spherical) particles, and less data is available for multi-size/irregular-shape particles. There are several analytical models available, which rely on the mean particle diameter and porosity of the bed in their predictions. Two different types of particles were used to investigate coolability of particulate beds at VTT, Finland. The first type is irregular-shape Aluminum Oxide gravel particles whose sizes vary from 0.25 mm to 10 mm, which were employed in the STYX experiment programme (2001-2008). The second type is spherical beads of Zirconium silicate whose sizes vary between 0.8 mm to 1 mm, which were used in the COOLOCE tests (Takasuo et al., 2012) to study the effect of multi-dimensional flooding on coolability.
In the present work, the two types of particles are used in the POMECO-FL and POMECO-HT test facility to obtain their effective particle diameters and dryout heat flux of the beds, respectively. The main idea is to check how the heaters’ orientations (vertical in COOLOCE vs. horizontal in POMECO-HT) and diameters (6 mm in COOLOCE vs. 3 mm in POMECO-HT) affect the coolability (dryout heat flux) of the test beds.
The tests carried out on the POMECO-FL facility using a bed packed with aluminum oxide gravel particles show the effective particle diameter of the gravel particles is 0.65 mm, by which the frictional pressure gradient can be predicted by the Ergun equation. After the water superficial velocity is higher than 0.0025 m/s, the pressure gradient is underestimated. The effective particle diameter of the zirconium particles is found as 0.8 mm.
The dryout heat flux is measured on the POMECO-HT facility using particulate beds packed with the same particles as in POMECO-FL. The dryout heat flux of the bed with aluminum oxide gravels under top flooding is found to be close to the prediction of the Lipinski model. The dryout heat flux increases by 51% when applying a 12-mm size downcomer. The dryout heat flux of the bed with zirconium particles test lies between the values predicted by the Reed model and Lipinski model. The use of the 12-mm size downcomer increases dryout heat flux by 16%.|
|Keywords:||Debris bed coolability, Effective particle diameter, Particulate bed, Dryout heat flux|
|Publication date:||07 Aug 2013|
|Number of downloads:||1340|