NDT Techniques for the Evaluation ofTRISO Fuel

Advanced gas cooled reactor designs utilizing Tristructural Isotropic (TRISO) fuels continue to be strong avenues for research and testing. However, concerns continue about fabrication defects that can lead to failures during operation. Internal defects in the multi-layer coating of the kernel can lead to fuel failure at the particle or pebble level. Layer integrity is the key to the reliability and usability of all TRISO-based fuel forms. During operation the integrated effects of fuel fissioning, radiation-induced material transformations, and internal pressurize buildup combine to grow and propagate pre-existing internal defects. The consequential failures may lead to the uncontrolled dissemination of fission products through the system. In addition to leading to costly cleanup and repairs of systems, such failures may jeopardize public health and erode public confidence in these technologies. These concerns will continue to exist without a cost effective and systematic means of inspecting every fuel particle to eliminate these failure modes.This proposal advocates for the development and demonstration of two non-destructive testing (NDT) methods for the evaluation and inspection of TRISO fuel particles to detect defects that typically occur in less than 1% of particles. The methodologies and equipment will be developed with the purpose of creating a novel inspection system or systems that can be utilized to further the development and introduction of advanced reactor designs. A successful design will have the capability to detect defects within TRISO fuel particles at a rate suitable for production volumes either individually or in concert and with a high degree of certainty for defect detection. This system or systems must have a capability for automated inspection and disposition of particles on an individual particle basis.The two inspection technologies that NovaTech proposes to evaluate are resonant frequency analysis and thermography. Both of these technologies are non-destructive inspection techniques that are capable of identifying subsurface defects such as cracks, delaminations and voids. However, each technique uses fundamentally different principals to arrive at results. NovaTech believes that in concert these two techniques can provide a robust, efficient and cost effective solution to inspecting TRISO fuel pellets.