Synergistic tellurium–caesium embrittlement of Type 316 stainless steel

Abstract

Austenitic stainless steels have become important high-temperature structural and containment alloys in applications ranging from industrial processes to energy generation and conversion. The AISI Type-300 series of iron–base austenitic stainless steels, in particular, is widely used as a barrier or primary containment material for both nuclear and fossil fuels operation at temperatures as high as 700 and 1,000 °C, respectively. Thus any observed deleterious effect of chemical environment on the alloy mechanical properties such as the ‘hot’ embrittlement of austenitic stainless steel by liquid zinc^1,2 is very important and, indeed, Old³ has mentioned that fission products such as caesium, cadmium and tellurium might embrittle the austenitic stainless steel cladding of fast reactor fuel pins in certain conditions. The few investigations of the high temperature mechanical behaviour of iron–base austenitic stainless steels in chemical environments intended to simulate in-reactor conditions have not positively identified any particularly severe chemomechanical degradation, such as that accompanying stress corrosion cracking or liquid metal embrittlement. We now report the observation of rapid, severe embrittlement of AISI 316 stainless steel by liquid tellurium–caesium mixtures in the temperature region 500–700°C. Our results were obtained using a test technique that involves radially deforming small ring specimens contained inside an environmental chamber by compressive loading at a uniform displacement rate. This ring compression test technique has the advantages of facile control of the chemical environment and ease of adaptation for work with irradiated materials.