SCC Propagation Rate of Type 304, 304L Steels Under Oceanic Air Environment

Corrosion integrity of canister in the concrete cask for spent fuel storage is very important because the canister serves to maintain the sealability over the storage period of 40 to 60 years. Natural exposure and accelerated corrosion tests of conventional stainless steels for canister, that are Type 304, 304L, and 316(LN), for concrete cask’s canister have been conducted by using many three Point Bending (3PB) test specimens and compared. The SCC propagation rates in Type 304 and 304L at the natural condition were about 1.2E−12 to 1.8E−11 m/s at the K (Stress Intensity Factor) range of 0.6 to 9.0 MPa√m, and that of the accelerate test (60 degrees C, 95%RHS., filled with NaCl mist) were about 1.0E−10 to 3.5E−9 m/s at the K range of 0.3 to 32 MPa√m. The SCC propagation rates under both natural and accelerated conditions were independent with K. Both da/dt values of the direct exposure test and of the under glass exposure test were in the same scattering band.