Aerosol retention in low-subcooling pools under realistic accident conditions

The POSEIDON-II experiments investigate the aerosol scrubbing by low-subcooling pools lo provide data to help predictive models. The experiments consist of 17 tests which examine the dependence of the decontamination factor (DF) on water height, carrier gas steam mass fraction and particle diameter. Selected experiments demonstrate the competition of individual aerosol removal mechanisms such as impaction and condensation at the injection point. The DF is found to increase significantly with water height and steam mass fraction. The data show that important aerosol retention occurs in low-subcooling pools, and hence the standard assumption of zero decontamination in hot pools is overly conservative. The data also appreciably reduce the uncertainty in aerosol scrubbing estimates for shallow pools ( < 2 m) when compared with best estimate models. This uncertainty is particularly important because a large fraction of the aerosols can escape shallow pools, whereas deeper pools are known to retain most of the aerosols. Results of computer simulations with the BUSCA code show a fair agreement with the data at low pool heights (with low DFs). but are non-conservative for larger heights. The discrepancy is believed to be due to the hydrodynamics model in the code which assumes a bubbly gas flow, whereas the actual regime is churn-turbulent with smaller gas residence times in the pool.