Experimental investigation on the impact of different thermodynamic parameters on the depletion behavior of nuclear aerosols in the IN-EX facility

Abstract

Fission products (FPs) released in the process of a severe loss of coolant accident can reach the containment – the last barrier against the leakage of radioactive isotopes to the surrounding environment – as airborne particles. Consequently, reliable assessment of a potential radiological source term requires in-depth knowledge of the aerosol behavior. The IN-EX facility at Forschungszentrum Jülich (FZJ, Germany) is built to study nuclear aerosol depletion behavior under accident scenarios by varying thermodynamic parameters (relative humidity, temperature and pressure). We performed a series of experiments using both, pure and mixed particles. The objective is to improve the understanding of aerosol depletion mechanisms and provide the latest data for optimization and validation of computational models for aerosol behavior.In the IN-EX experiments, SnO2 and CsI represent the insoluble and soluble particles released from the damaged core, respectively. In the case of mixed particles, in order to figure out the effect of varying mass composition on the aerosol behavior, we used the mass compositions of CsI and SnO2 in the ratio of 3:7 and 6:4 in this paper. In this work, we measured the mass concentration and size distribution, and derived the corresponding aerosol removal rate to analyze the data. During the experiments on CsI aerosols, we observed that the aerosol removal rate is accelerated by an increase in relative humidity, while relative humidity seems to have no effect on the depletion of SnO2 aerosol. Furthermore, pressure or temperature appears to have no significant effect on the depletion behavior both of SnO2 and CsI aerosols. Combining with the results of pure substances, we investigated the regularity of the depletion behavior of mixed aerosols. In general, SnO2 has the highest aerosol removal rate, while CsI has the lowest one. The removal rate of the mixture is between SnO2 and CsI. The components in the mixture with a high mass fraction determine the depletion behavior of this mixture. Particularly in the condensed state, we found almost no difference in the aerosol removal rate of either pure substances or mixtures.