Study of the corrosion behaviour of beryllium in solutions representative of Portland cement and magnesium phosphate cement

Abstract

Metallic beryllium is an attractive material for nuclear applications, e.g. thermal reactor and fusion reactors. After use, activated beryllium waste will need to be disposed of in a geological disposal repository. One option for the treatment and conditioning of the beryllium waste could be the direct emplacement of pieces of beryllium in a cementitious matrix. In these conditions, beryllium corrodes due to reaction with water to produce hydrogen, and beryllium hydroxide, leading to possible loss of the waste containment. To gain more information on the anaerobic corrosion of beryllium, Electrochemical Impedance Spectroscopy and hydrogen measurement by gas chromatography were used, while beryllium samples were immersed in solutions representative of promising matrices (Portland cement (OPC, pH 13.5) and magnesium phosphate cement (MPC, pH 8.1)) for maximum one year. At the beginning of the test (< 180 days), both techniques showed that the beryllium corrosion rate was lower in OPC solution than in MPC solution. At longer term (> 180 days), the corrosion rate decreased sharply in MPC solution, while the corrosion rate in OPC solution remained stable. Therefore, at longer term, the lower corrosion rate was observed in MPC solution. The reason of this corrosion rate decrease comes from the formation of a passive layer composed of Be(OH)₂ (inner part) and KBePO₄·H₂O crystals (outer part) at the surface of beryllium in MPC solution, while no protective corrosion product layer was present on the metal surface in OPC solution. In that later case, pitting corrosion was observed in addition to the dissolution of beryllium species in solution probably in the form of Be(OH)₄²⁻.