Corrosion of 316L exposed to highly concentrated borated water used as shield in nuclear fusion experimental reactors cooling circuits

Borated water is used as a shield in nuclear fusion cooling circuits. General corrosion, activated corrosion products (ACPs) formation and stress corrosion cracking initiation of 316 L steels exposed to ultrapure water (UPW) or 8000 ppm B water at 80 °C were tested. A Ni enriched sub-oxide layer, a transition layer and oxide layer were observed using advanced characterisation (STEM-EELS, APT). The oxide formed in UPW was protective (Cr:O 40:45), the oxide formed in 8000 ppm B was non-passivating. 8000 ppm B led to higher release of Fe, Cr and Mo, 316 L was more prone to SCC initiation and enhanced ACPs formation.