In this study, the aerosol release from the silver-indium-cadmium control rods during the air-ingress phase of the QUENCH-18 bundle test was investigated both experimentally and by using simulation tools. During the QUENCH-18 test, the aerosol mass size distribution was measured using two Berner low pressure impactors, aerosol samples were collected on filters, and the particle number size distribution was monitored online with an Electrical Low Pressure Impactor (ELPI). After the experiment, the elemental composition of the aerosol samples was determined using inductively coupled plasma optical emission spectrometry. The first released aerosol particles contained mostly cadmium and afterwards, also silver was released with cadmium in significant amounts, with the indium concentration staying at lower level. The MELCOR 2.2 code was used to simulate the aerosol deposition in the QUENCH facility in order to assess the total release of the control rod materials during the test. Based on the measurement and simulation results, the total releases of cadmium, silver and indium during the test were determined to be 9.0 g, 6.5 g, and 1.2 g, ... mehr respectively. A thermodynamic equilibrium model was used to investigate the speciation of the control rod material in the test conditions. The calculations indicate that the aerosol particles measured during the first aerosol release consisted mostly of cadmium oxide and during the main release phase, the main aerosol release consisted mainly of Cd and Ag compounds with smaller amounts of indium.