Aerosol formation from liquid impingement in liquid metal cooled nuclear reactor systems

Abstract

Lead-bismuth eutectic (LBE) is chosen as coolant for the future MYRRHA reactor. Aerosols formed in nuclear reactors during operations can jeopardize human health and plant operations in case of accidents. Aerosol models are available for water, - and sodium based reactors, but not for LBE. Therefore, this thesis presents a pilot study on the most important aerosol formation mechanism in MYRRHA: impingement of LBE droplets on surfaces.

A ‘SPLAT setup’ is built in which LBE droplets are dispensed and impinge on liquid and solid surfaces. Impingement is characterized with a high-speed camera; the resulting aerosol particle size distribution (PSD) was determined with a wide range aerosol detector. Liquid impingement is studied for large (Ø: 1.5 – 3 mm) and small droplets (Ø < 1.5 mm) with velocities between 1.82 – 2.53 m/s. Recordings of the liquid surface show splashing, which increases with increasing droplet diameter and impact velocity. Dry solid surface impingement shows droplet spreading. Successive LBE droplets (Ø: 2.90 ± 0.02 mm), impacting a liquid surface generate aerosol particles with diameters < 250 nm. The PSD maximum is located at 100 nm. On a dry solid surface, diameters up to 100 nm are recorded, with the PSD peak at 28 nm.

The results of this thesis show that liquid impingement of LBE droplets can pose a safety hazard as significant amounts of sub µm aerosol particles are generated. While most splashing is observed with the liquid surface, dry solid surface impingement generates the smallest aerosols.