Hot-corrosion-induced cracking of fuel pin cladding tubes of Cr-Ni steels

Abstract

Stress rupture experiments were conducted in tube burst and tensile tests under the influence of S, Se, Te, I and Cs 2Te, especially in combination with NiO which was employed to establish a relatively high oxygen potential. The stress levels were chosen in such a manner that a rupture life of about 1 h was achieved (without the influence of the reactive species) at 700, 800, 900 and 1000°C, and of about 100 and 500 h at 700°C. The cladding tube materials tested were X10CrNiMoTiB15 15 (1.4970), X5NiCrTi25 10 (RGTX1), X10NiCrMoB25 10 (RGTX2) and X17CrMoVNb121 (1.4914). Effects and phenomena that could be due to stress corrosion cracking were observed mainly in 1 h tests at 700°C, under the influence of I + NiO and Cs 2Te + NiO. There was a severe reduction in time-to-failure and elongation at fracture. The austenitic steels RGTX1 and 2, which are particularly poor in Cr (~10 wt%), were found to be most sensitive to stress corrosion cracking. The martensitic-ferritic steel 1.4914 appeared to be completely insensitive. Grain boundary attack and separation seemed to be responsible for the effect of stress corrosion cracking.