Measurement of the Nickel/Nickel Oxide Transition in Ni-Cr-Fe Alloys and Updated Data and Correlations to Quantify the Effect of Aqueous Hydrogen on Primary Water SCC

Abstract

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Using tapered specimens to study the effect of hydrogen and surface finish on SCC initiation in Alloy 182 under boiling water reactor conditions

“…The tests were performed in high-purity high-temperature water under low-flow condition (six autoclave exchanges per hour) at 274°C with 10, 50, 253, 600 and 2000 ppb DH, respectively. The DH concentration in the water at the Ni/NiO phase transition line at 274°C was measured to be 253 ppb [3], thus, the chosen DH concentrations represent the Ni area (600 and 2000 ppb), Ni/NiO phase transition (253 ppb) and NiO area (10 and 50 ppb). The corresponding range of redox potentials of the environment is from −458 (10 ppb DH) to −583 mV (2000 ppb DH), the redox potential at the Ni/NiO transition line is −535 mV.…”

“…equilibrium electrochemical electrode potential of the Ni/NiO electrode, Ni + H 2 O ↔ NiO + 2H + + 2e − ) has been observed at 320-360°C [1,2]. This thermodynamic boundary and related ECP corresponds to a specific critical hydrogen content of the H 2 /H 2 O electrode that is predicted to decrease from 2.3 ppm DH at 360°C to 0.25 ppm DH at 274°C [3,4]. In BWRs with moderate hydrogen water chemistry (HWC) or noble metal chemical addition (NobleChem) [5], the DH concentration is close to this peak [6].…”