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| NKS Programme Area: | NKS-R | | Research Area: | Severe accidents | | Report Number: | NKS-286 | | Report Title: | COOLOCE debris bed experiments and simulations investigating the coolability of cylindrical beds with different materials and flow modes | | Activity Acronym: | DECOSE | | Authors: | Eveliina Takasuo, Tuomo Kinnunen, Stefan Holmström, Taru Lehtikuusi, | | Abstract: | The COOLOCE experiments aim at investigating the coolability of debris beds of different geometries, flow modes and materials. A debris bed may be formed of solidified corium as a result of a severe accident in a nuclear power reactor.
The COOLOCE-8 test series consisted of experiments with a top-flooded test bed with irregular gravel as the simulant material. The objective was to produce comparison data useful in estimating the effects of different particle materials and the possible effect of the test arrangement on the results. It was found that the dryout heat flux (DHF) measured for the gravel was lower compared to previous experiments with spherical beads, and somewhat lower compared to the early STYX experiments. The difference between the beads and gravel is at least partially explained by the smaller average size of the gravel particles.
The COOLOCE-9 test series included scoping experiments examining the effect of subcooling of the water pool in which the debris bed is immersed. The experiments with initially subcooled pool suggest that the subcooling may increase DHF and increase coolability. The aim of the COOLOCE-10 experiments was to investigate the effect of lateral flooding on the DHF a cylindrical test bed. The top of the test cylinder and its sidewall were open to water infiltration. It was found that the DHF is increased compared to a top-flooded cylinder by more than 50%. This suggests that coolability is notably improved.
2D simulations of the top-flooded test beds have been run with the MEWA code. Prior to the simulations, the effective particle diameter for the spherical beads and the irregular gravel was estimated by single-phase pressure loss measurements performed at KTH in Sweden. Parameter variations were done for particle size and porosity used as input in the models. It was found that with the measured effective particle diameter and porosity, the simulation models predict DHF with a relatively good accuracy in the case of spherical particles. In the case of irregular gravel, for which the uncertainties of porosity and particle diameter are larger, the discrepancy between the simulations and experiments is greater. | | Keywords: | severe accident, core debris, coolability, dryout, COOLOCE experiments, MEWA code | | Publication date: | 15 Jul 2013 | | ISBN: | ISBN 978-87-7893-361-4 | | Number of downloads: | 3232 | | Download: |  NKS.286.pdf |
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