The Corrosion Behavior of High-Temperature Alloys During Exposure for Times up to 10 000 h in Prototype Nuclear Process Helium at 700 to 900°C

A corrosion program is being carried out to establish the long-term corrosion behavior of candidate alloys for the prototype nuclear process (PNP) reactor primary circuit. Results are presented for corrosion tests performed in impure helium over the temperature range of 700 to 900 °C for times up to 10000 h. In the helium atmosphere containing 0.5 to 1.5 μbar H₂O, 15 μbar CO, 20 μbar CH₄, and 500 μbar H₂, the three main PNP reference alloys—Inconel-617, Nimonic-86, and Hastelloy-X—exhibit excellent corrosion resistance with the carbon uptakes of <0.02% in 10 000 h at temperatures up to 900°C. Differences in behavior are related to the composition and morphology of protective surface scales and minor variations in gas impurity levels during test startup. The influence of variations in alloy composition on the long-term stability of these oxide scales is also discussed.