PNNL

Abstract

This document summarizes the activities performed and progress made in FY-03. Various approaches for automating the particle fuel production QC process using on-line nondestructive methods for higher reliability were evaluated. In this first-year of a three-year project, surrogate fuel particles made available for testing included leftovers from initial coater development runs. These particles had a high defect fraction and the particle properties spanned a wide range, providing the opportunity to examine worst-case conditions before refining the inspection methods to detect more subtle coating features. Particles specifically designed to evaluate the NDE methods being investigated under this project will be specified and fabricated at ORNL early next reporting period. The literature was reviewed for existing inspection technology and to identify many of the fuel particle conditions thought to degrade its performance. A modeling study, including the electromagnetic and techniques, showed that the in-line electromagnetic methods should provide measurable responses to missing layers, kernel diameter, and changes in coating layer thickness, with reasonable assumptions made for material conductivities. The modeling study for the ultrasonic methods provided the resonant frequencies that should be measured using the resonant ultrasound technique, and the results from these calculations were published in the proceedings for two conferences. The notion of a particle quality index to relate coating properties to fabrication process parameters was explored. Progress was made in understanding the fabrication process. GA identified key literature in this area and Saurwein (2003a) provided a literature review/summary. This literature has been reviewed. An approach previously applied to flexible manufacturing was adopted and the modification and development of the concepts to meet TRISO particle fuel manufacturing and QA/QC needs initiated. This approach establishes relationships between key process parameters and part parameters, including "defects" for each manufacturing step - which in this case is a coating layer. This activity will continue in year two, when an initial evaluation will be made using available process and particle data. Radiographic and Computed Tomography (CT) techniques were developed and refined to examine individual particles and batches of up to about 30 to 40 particles for kernel diameter, coating layer thickness and spatial uniformity. These results are essential for developing the defect library of characterized particles that will be used to calibrate the high-speed nondestructive measurement methods that are found capable of automatically detecting particles having properties outside a specified range. The in-line inspection methods evaluated include the electrical property measurement methods traditionally referred to as eddy current and capacitance (or dielectric) in the nondestructive test methods literature. An eddy current technique was developed and evaluated on stationary particles. Good correlation was found between the eddy current measurements and the radiographically determined particle dimensions. Initial measurements on fuel compacts using the eddy current approach showed that these materials are amenable to electrical inspection and that significant coil impedance variability can be observed among different samples.