X-Ray Radiography: An Alternative Method for Determining HTR Fuel Particle Coating Layer Thickness and Density

The HTR TRISO particle consists of a fissile kernel and surrounding layers, whose density and thickness are among the key fuel parameters. Destructive methods i.e. the sink float method and image analysis of ceramography, were developed in the past and are still used to evaluate these particle parameters. Although exhibiting great accuracy, these methods generate effluents and wastes, and are extremely cost/time consuming. In the framework of the AREVA NP HTR R&D program, the development of nondestructive evaluation methods as alternatives to destructive methods is carried out and aims at a new HTR Fuel QC strategy. In this scope, an innovative method was developed to automatically measure particle layer density and thickness from X-Ray Phase Contrast Imaging (PCI). First tested at the European Synchroton Radiation Facility (ESRF), this method was then applied to a custom built industrial demonstrator. Comparisons between the density and thickness values obtained by the developed method and their corresponding values obtained with destructive methods justify progressing to the validation phase. Particle samples were selected among the particle batches that were characterized by destructive methods. Layer density and thickness were determined by the X-Ray based technique on the industrial demonstrator as well as at the ESRF. Correlation levels obtained from this benchmark demonstrated that both parameters can be confidently measured by the developed method. Additionally, it is important to stress that this technique provides the opportunity to directly determine buffer density on finite particles as opposed to the sink float method. Thanks to its accuracy, its rapidity and its absence of waste generation, it is planned to implement the X-Ray thickness and density measurement method on the French lab scale fuel line. It was also decided to enter the characterization work package of the IAEA Coordinated Research Project 6 in order to benchmark the AREVA NP method with foreign techniques and materials.