A hydrogen transport and oxidation study of scandium-modified 304L stainless steel in simulated pressurized water reactor primary water

Trace Sc addition was investigated as a strategy for regulating hydrogen transport and oxide-film evolution in 304 L stainless steel exposed to simulated PWR primary water. This work establishes an integrated experimental-atomistic link between Sc-induced microstructural heterogeneity, hydrogen redistribution, and oxide-film defect chemistry. The 304 L + 0.19 wt% Sc steel exhibited a lower apparent hydrogen diffusivity at 300°C, decreasing from (3.91 ± 0.20) × 10 −11 to (2.88 ± 0.14) × 10 −11 m 2 s −1 . Thermal desorption analysis revealed that the total hydrogen content decreased from 16.378 to 14.272 wt. ppm, accompanied by a reduction in the low-temperature desorption component and an enhancement of the higher-temperature components, indicating a redistribution of hydrogen from mobile/weakly trapped states toward more stable trapping sites. Microstructural characterization showed that Sc addition refined the average grain area from 95.27 to 21.61 μm 2 , increased the GND density from 68.236 × 10 16 –100.552 × 10 16 m −2 , and promoted the formation of Sc-rich P/S inclusions. After exposure to simulated PWR primary water at 320°C for 384 h, the Sc-containing steel developed a thinner oxide layer, with the average thickness decreasing from 0.46 ± 0.111–0.31 ± 0.092 μm. Despite this reduced thickness, the oxide film exhibited a higher film resistance (9.42 × 10 5 Ω·cm 2 ), a higher charge-transfer resistance (3.03 × 10 6 Ω·cm 2 ), and a lower donor density (1.171 × 10 17 cm −3 ) than on conventional 304 L. Atomistic calculations revealed that Sc lowered the hydrogen defect formation energy from 0.34 to 0.15 eV and promoted localized Sc-O bonding. These results demonstrate that trace Sc addition suppresses hydrogen transport and promotes the formation of a thinner yet more protective oxide film on 304 L stainless steel.