Development of an in-pile diameter gauge based on an electrical impedance measurement

The capability to perform real-time noncontact diameter measurements in test reactors could be leveraged to experimentally measure phenomena of interest to the nuclear energy community. Specific phenomena of interest include fuel-cladding interaction and the complex dimensional changes other materials undergo during irradiation. The work presented here outlines the development of an in-pile electrical impedance-based diameter gauge that has been under development at Idaho National Laboratory (INL). This sensor is based on the measurement of an electrical impedance between two electrodes. Changes in the sample diameter result in changes in the capacitive coupling between the electrodes. The sample diameter can be determined through measuring the electrical impedance between electrodes and the use of analytic and/or numerical models. Therefore providing a noncontact diameter measurement technique with a wide range of applications to in-pile measurements. A test apparatus has been constructed to perform out-of-pile tests of this sensor design. Promising measurements have been observed from the preliminary experimental results, indicating a diameter measurement error on the order of 20 µm. Future work will continue to quantify the uncertainty and sensor performance under a variety of conditions.