Development and validation of aerosol effective density model under severe accidents at NPP

Aerosols are one of the key forms of fission products formed during beyond design basis accidents with fuel melting (severe accidents). Modeling the transfer and deposition of fission product aerosols in the containment plays an important role in determining the amount of fission product release into the environment, while the deposition of aerosols is largely determined by their density. To date, the key experimental program in which the formation and process of transfer of radioactive fission product aerosols during the melting of fuel samples has been studied is the Phebus-FP experimental program. Based on the results of this program, data on the size distribution of fission product aerosols, data on the composition of aerosols, and estimates of the density of aerosol particles were obtained. The authors of this work have developed a method for assessing the effective density of multi-component aerosols formed during beyond design basis accidents at NPPs. In this work, the particle effective density was assessed using the proposed calculation method for three tests of the Phebus-FP experimental program: FPT-1, FPT-2 and FPT-3. The effective density of aerosol particles is proposed to be modeled in two approximations: "continuity" and "porosity". The obtained estimates of the effective density values of radioactive aerosols of fission products were used to simulate the transfer of aerosols in the FPT-1/2/3 containment using the MAVR-TA code.