In-Situ NDE System for Structural Integrity Inspection of Nuclear Graphite Components

The methods are sought for real-time in-situ monitoring of the irradiation performance of graphitic components in the cores of next-generation nuclear plants. Such structural monitoring is necessary because radiation-induced damage to graphite can lead to mechanical degradation, dimensional change, and porosity, which can compromise the safety of the operation of the reactor. The information on the graphite degradation can be used by nuclear reactor operators to improve the reliability, sustain the safety, and extend the life of current and future reactors. A new device is proposed, based on a Compton imaging tomography technology recently pioneered. Using this approach, the structure is scanned by a planar X-ray beam, and the 3D density profile of the material is reconstructed from the Compton-scattered X-ray images recorded at multiple positions of the beam. In contrast to existing approaches, this technology permits much quicker and less expensive examination of nuclear graphite condition, without disrupting the integrity of nuclear components. In Phase I, a novel nondestructive evaluation technology has been developed and demonstrated for inspection of nuclear graphite components, with emphasis on future use in gas-cooled next-generation nuclear plants. A thorough analysis of nuclear graphite inspection needs in the context of next generator nuclear plants operation was completed, and the required evaluation performance parameters were formulated to address the customer needs. Based on the target performance parameters, a prototype inspection system has been designed via modeling and system analysis, and its feasibility demonstrated experimentally by imaging defects and cracks in samples of several types of nuclear graphite, with density resolution ~1% and penetration depth ~5 cm, with resolution ~2 mm. In Phase II, plans call for development and optimization of a system design with enhanced evaluation performance, and fabrication of a standalone system for graphite inspection that will be tested at the end of the project at project subcontractor, who is responsible for next-generation nuclear plant development. Commercial Applications and Other Benefits: In addition to the inspection of graphite components in reactor cores, this approach (with slight modifications) can be used for evaluating the integrity of refractory, ceramic, and composite components in nuclear reactors. Due to its small size, the system can also be used in oil and gas applications for borehole wall inspections and in refineries for pipeline maintenance and monitoring.