Prediction of Dryout Heat Flux of Volumetrically Heated Particulate Bed Packed with Multi-Size Particles
NURETH-14 - 2011 September 25-30

Presented at:
2011 September 25-30
Toronto, Canada
Session Title:
C6-2 Experimental Debris Bed Cooling

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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