Initiation and Propagation of Stress Corrosion Cracking of Stainless Steel Canister for Concrete Cask Storage of Spent Nuclear Fuel

Resistance to atmospheric stress corrosion cracking (SCC) and crevice corrosion was examined for various candidate canister materials in the spent fuel dry storage condition using concrete casks. A constant load SCC test was conducted on the candidate materials in air after deposition of simulated sea salt particles on the specimen gauge section. UNS S31260 and UNS S31254, highly corrosion-resistant stainless steels (SS), did not fail for more than 46,000 h at 353 K with relative humidity of 35%, although UNS S30403 and UNS S31603 SS failed around 500 h by SCC. Crack growth measurement was done to explain this result. Cracking on S31603 propagated around 3 × 10–10 m/s at K values larger than 10 MPa·m0.5 at 353 K with RH = 35%. S31260 SS showed a crack growth rate of 4 × 10–13 m/s at the same condition. Crevice corrosion potentials of S31260 and S31254 SS became larger than 0.9 V vs. saturated calomel electrode (SCE) in synthetic seawater at temperatures below 298 K, while those of S30403 and S31603 SS were less than 0 VSCE at the same temperature range. No rust was found on S31260 and S31254 SS specimens at temperatures below 298 K in the atmospheric corrosion test consistent with the temperature dependency of crevice corrosion potential. From the test result, the critical temperature of atmospheric corrosion was estimated to be 293 K for both S31260 and S31254 SS.