Through-Tank Ionic Conductivity Measurement Feasibility Study

摘要

An approach was investigated to detect the presence of ionic-conductive pathways in steel liners for Single Shell Tanks (SSTs) used to store nuclear waste. An ionic pathway might be present because of a crack at a level below the waste, which is difficult to detect. The approach uses Electrochemical Impedance Spectroscopy (EIS), in which measurements are made on a working electrode immersed in the waste in the tank using counter and reference electrodes embedded in the ground outside of the tank in the ground. An equivalent electrical circuit was successfully developed to simulate the response of the system with and without the presence of a crack. Experiments using cans embedded in dirt in a plastic tub and a large drum buried in soil were performed. The measurements were able to detect the presence of cracks intentionally created in the cans and the EIS response was similar in form and magnitude to that predicted by the equivalent circuit, which validated the model and the values of the parameters used to determine the model circuit element values. However, both the experiments and the simulation modeling predict that the approach will have limited ability to detect small defects in a large structure, such as cracks in the SST steel liner, because the resistance to current flow through the sound part of a can or tank liner decreases as the area increases..