EddyGraph: A Modular, Precision Swept Frequency Eddy Current Based Graphite Inspection System

The development of advanced inspection technologies for graphite components in High Temperature Gas Reactors (HTGRs) and Molten Salt Reactors (MSRs) is crucial for improving the safety, efficiency, and longevity of next-generation nuclear reactors. Graphite components play vital roles in neutron moderation and structural support but are subject to degradation from molten salt erosion, thermal stress, and surface wear. In-situ, high-resolution nondestructive evaluation (NDE) technologies, such as visual and eddy current systems with up to 500-micron resolution, are essential to assess these components' condition under extreme conditions, ensuring the safe operation and growth of the U.S. nuclear industry. The EddyGraph system aims to address the challenge of efficiently inspecting graphite components in nuclear reactors, particularly in High Temperature Gas-cooled Reactors (HTGRs) and Molten Salt Reactors (MSRs), where traditional methods struggle with complex geometries and harsh environments. The system will consist of multiple specially designed eddy current (EC) sensors housed inside stainless-steel housing integrated into an articulating arm, enabling rapid scanning of the entire fuel channel bore. A machinelearning-based inversion model will be used for the interpretation of eddy current data measured on curved surfaces, capable of identifying and locating the presence of multiple damage mechanisms. First, a high-fidelity finite-element model of a representative HTGR graphite reflector block will be developed which will include typical damages expected in such components. Second, this model will be used to optimize the eddy current coil parameters to ensure sensitivity to typical damage types anticipated. Third, the simulated eddy current data will be used to train a machine-learning model for inversion. Fourth, the forward model along with the machine learning-based inversion model will be used to demonstrate the feasibility of the proposed technique. Fifth, a basic prototype of the proposed system will be developed to demonstrate the capability of the proposed technology on a simple curved graphite block. In phase II, a fully functional prototype with radiation-hardened hardware and related software will be developed and tested on irradiated graphite components. The results will be used to refine the prototype and inversion model. In Phase III, a commercial version of the system will be developed. The proposed technology can also be used for rapid inspection of critical graphite structures in various industries like aerospace, manufacturing, and semiconductors.