The QUENCH-18 test was conducted at KIT in the autumn of 2017 with the primary aim to investigate the oxidation of M5^® cladding material in air/steam mixture, following a limited pre-oxidation in steam and to achieve a long period of air ingress conditions to promote the interaction of the cladding with nitrogen. The experiment bundle also featured two Ag-In-Cd control rods and aerosol measurements were also conducted during the test in order to investigate the effect of the oxygen and steam starvation on the timing, temperature and the composition of the release of control rod materials. The aerosol measurements were performed using both online measurement devices and particle sampling for later analysis. The aerosol sample was obtained from the QUENCH facility exhaust pipe and diluted using an ejector diluter. Electrical low pressure impactor was used for the online monitoring of the particle concentration during the experiment. The aerosol particles were sampled during the measurement to three Nuclepore membranes. In addition, two Berner low pressure impactors were used for obtaining particle mass size distributions during the test. The samples were analyzed after the experiment with Scanning Electron Microscopy and Energy Dispersive X-ray (SEM/EDS) to obtain the mass of the released control rod materials during the test.

According to the measurement results, first release of Ag-In-Cd materials took place during the air-ingress phase of the test, at the temperature 1350 K. The measurement of the aerosol release lasted approximately 30 minutes and was terminated prior to quenching of the bundle. The SEM/EDS analysis of the filter samples indicated that the first release of aerosol consisted mostly of cadmium. Afterwards, also silver and small amount of indium were released. Additionally, an estimate for the mass size distribution for each of the control rod material was obtained, with a media particle diameter of 1.8 μm. The size and formation process coincided well with the previous aerosol investigation in QUENCH-13. However, the composition of the released control rod materials was significantly altered.