Diagnostics of Chlorine Induced Stress Corrosion Cracking Using Laser Ultrasonics

The stainless steel canister inside a dry cask storage system (DCSS) used to store spent nuclear fuel is at risk for chlorine-induced stress corrosion cracking (SCC), especially near welds and at storage sites exposed to high humidity. It is highly desirable to have a viable technique for in-situ nondestructive evaluation of SCC, specifically to measure the depth of the crack along its length. Laser ultrasonic testing (LUT) has been applied to meet the demanding needs of canister inspection. LUT is a noncontact method for performing ultrasonic testing. It can measure crack depth with high accuracy. The components are resistant to the high-radiation, high-temperature environment inside the cask. The measurement head is fiber-delivered and can be miniaturized to fit into the tight spaces inside the cask. We have demonstrated the feasibility of measuring the length and depth of individual fatigue and stress corrosion cracks in realistic test samples. Concepts have been developed for overcoming the technical and integration challenges associated with implementing our technique in dry cask storage systems. During Phase II we will conclude the technology development and design, assemble and test a prototype laser ultrasonic measurement system that will be integrated onto a robotic crawler and tested on a realistic canister mockup at the Electric Power Research Institute. We will also expand our outreach to cask suppliers, nuclear utilities and inspection service providers. The safe storage of spent fuel is of great importance for the nuclear power industry and is a priority for insuring public safety. Our approach will be a significant advance in insuring the integrity of stored nuclear fuel containers. Our technique can also be adapted for the inspection of piping and other components used in nuclear and conventional power plants. The end users in both cases will be the electric utility companies which operate the power plants, while the direct customers would be inspection companies that perform on-site inspections. The safe storage of spent nuclear fuel is a high priority to the nuclear industry and to society as a whole. We propose to develop a technique for nondestructive evaluation that will help to determine the integrity of fuel storage containers.