Characterizing stress corrosion cracking in stainless steel using nonlinear resonant ultrasound spectroscopy

During disposal, spent nuclear fuel rods are placed into stainless steel containers and may be stored this way for decades. In order to ensure there is as little radiation leakage as possible, the structure of the stainless steel needs to be evaluated and possible damage detected. In particular, one type of damage these containers are particularly susceptible to is stress corrosion cracking (SCC). Traditional (linear) evaluation methods can detect open cracks but often a closed portion of the crack extends further, compromising the air tight seal sooner. To this end, it has been proposed to use Nonlinear Resonant Ultrasound Spectroscopy (NRUS) to quantify the degree of cracking in a structure. In order to prove this concept, cylindrical 304L stainless steel rods were immersed in a heated 42% MgCl2 solution to induce SCC in an accelerated manner to simulate the damage that is likely to occur on the actual containers. The rods were removed after different lengths of exposure. NRUS measurements were then conducted for longitudinal modes in the rods.