Conductivity Profiling of Graphite Moderator Bricks From Multifrequency Eddy Current Measurements

Abstract

This paper presents a novel system for mapping the through-wall electrical conductivity profiles of graphite moderator bricks that make up the core of an Advanced Gas-Cooled Reactor. Multi-frequency eddy current measurements were used to reconstruct the conductivity profiles as a function of depth from the bores of different graphite bricks. The study was carried out using a modified Levenberg Marquardt algorithm, along with a finite element based forward model. First, the algorithm was tested using a laboratory graphite sample with known electrical conductivity profile. Secondly, real datasets from one of the operating Advanced Gas-Cooled Reactors was collected and then used for reconstruction. The results in this study were compared with measurements from trepanned graphite samples taken from the reactor cores, and showed reasonable agreement in multiple cases, suggesting that this method could be a viable tool for non-destructively assessing the condition of the graphite core in Advanced Gas-Cooled Reactors.