Conference Proceedings Paper
Prediction of Dryout Heat Flux of Volumetrically Heated Particulate Bed Packed with Multi-Size Particles
NURETH-14 - 2011 September 25-30
Weimin Ma (Royal Institute of Technology)
This paper presents MEWA code calculations for the experiments performed on the POMECOHT
facility to investigate the dryout heat flux of various particulate beds, with the objective to
interpret the experimental data and validate the code. The code is then applied to coolability
assessment for ex-vessel debris beds related to severe accident scenarios of a boiling water
reactor (BWR). The characteristics of a prototypical debris bed, such as multidimensionality and
multiple particle sizes are emphasized in this study. The volumetrically heated particulate beds
of the POMECO-HT experiments are packed with multi-size particles and equipped with a
downcomer to investigate the bottom-fed coolability by natural circulation which demands 2D
simulation. The results show that the MEWA code is capable of predicting the coolability of the
bed with a downcomer (2D) as well as the top-flooding bed whose dryout heat flux can also be
predicted by the Reed model (1D). Given the effective particle diameter (1 mm) and porosity
(0.45) defined from a few FCI tests, the ex-vessel debris beds for a BWR chosen here are
coolable with varied margins: i) compared with a top-flooding bed (spreading over the entire
floor of the cavity), the cylindrical configuration with an annular-gap water supply enhances the
coolability comparison , but the gain is marginal since the large diameter of the bed prevents the
side coolant from flowing into the center of the bed; ii) a heap-like debris bed reduces rather than
improves coolability due to its considerable height and base diameter; iii) a stratified debris bed
with a fine-particle layer on the top may challenge the coolability.
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