Corrosion of aluminium in the aqueous chemical environment of a loss-of-coolant accident at a nuclear power plant

Abstract

Aluminium corrosion is a significant concern in the aqueous chemical environment of the reactor containment building following a hypothetical loss-of-coolant accident (LOCA) at a nuclear power plant. Aluminium corrosion may lead to the formation of precipitates that can, in combination with insulation debris, block the recirculation sump screens. This study investigated aluminium corrosion experimentally at both bench and pilot scale under conditions representative of several types of nuclear power plants. Evidence of corrosion was determined using aqueous concentrations measured with inductively-coupled plasma (ICP) spectrometry and surface examinations using scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), X-ray photoelectron spectrometry (XPS), X-ray fluorescence (XRF), and X-ray diffraction (XRD). Corrosion proceeded slowly at pH near 7, but more rapidly at higher pH when the representative pipe insulation material was fibreglass. However, when calcium silicate pipe insulation was introduced into the system, corrosion became insignificant even at pH values near 10. Experimental evidence indicates that the calcium silicate insulation released a significant amount of silicate to the solution. Silicate formed a passivation layer composed of Al 2OSiO 4 with a thickness of more than 10 nm, and this layer effectively inhibited corrosion.