Chemical reactions of caesium, tellurium and oxygen with fast breeder reactor cladding alloys: Part I — The corrosion by tellurium

Abstract

The corrosion of the alloys PE16, M316 and FV448 by liquid Te in sealed capsules has been studied after 168 h at 948 K both with and without a buffer of Mo/MoO 2. This buffer sets the thermodynamic oxygen potential at Δ G ̄ o 2 = −417 kJ mol −1 O 2 . All three alloys were severely corroded and the extent was in the order M316 > PE16 = FV448. Oxygen diminished the extent of corrosion but did not change the order. All three alloys carried two layers of corrosion products on top of a damaged metal surface. The outer layer contained Fe 1.5 Ni 1.5 Te 2 for PE16 but Fe 2.25 Te 2 for M316 and FV448. The inner layer contained Cr 2Te 3 for all three alloys. The damaged metal surface was largely Cr 2Te 3. The substrate alloys (PE16 and FV448) were penetrated intergranularly by Te, but M316 exhibited an even band of Cr-depleted steel. The results are explained by the diffusion of Te into the alloy and the diffusion of the alloy components in the opposite direction. The corrosion is exacerbated by dissolution of alloy into the liquid Te from which the metal tellurides subsequently precipitate.