An Experimental Study on the Retention of Graphite Dust Aerosol in Pool Scrubbing and the Possible Application in HTGRs

Abstract

Owing to the inherent safety, the modular high-temperature gas-cooled reactor (HTGR) eliminates the possibility of severe accidents in principle. Therefore, the source term is the main concern for HTGR accidents. Especially, the graphite dust problem, arising from the abrasion of fuel pebbles, complicates the evaluation of source terms. In the water ingress accidents, the graphite dust may be released to the containment during the overpressure discharge, which not only contributes to the source term but also makes trouble for post-accident measures. In this work, we consider the possibility to develop a pool scrubbing measure to retain graphite dust and fission products for the overpressure discharge of HTGR. A scrubber is set up with aerosol particle concentration measurement at both the inlet and outlet, which enables us to determine the decontamination factor (DF). By conducting a series of experiments for different submergence depth and particle size, it is demonstrated the DF value increases with the increase of submergence depth. When the submergence depth is 105 cm, the retention efficiency of graphite particles larger than 2 μm exceeds 96%. Our previous study has shown due to a fragmentation effect, most of the graphite particles released during the overpressure discharge are below 2 μm, while the DFs for these small particles fall below 20. The experimental results show that the pool scrubbing technology can efficiently retain the graphite particles for the overpressure discharge in HTRGs. More efforts are still needed to effectively improve the DF for graphite particles below 2 μm.