The next generation nuclear power/advanced gas reactor (NGNP/AGR) fuel development and qualification program included the design, installation, and testing of a 6-in. diameter nuclear fuel particle coater to demonstrate quality tri-structural isotropic (TRISO) fuel production on a small industrial scale. Scale-up from the laboratory-scale coater faced challenges associated with an increase in the kernel charge mass, kernel diameter, and a redesign of the gas distributor to achieve adequate fluidization throughout the deposition of the four TRISO coating layers. TRISO coatings are applied at very high temperatures in atmospheres of dense particulate clouds, corrosive gases, and hydrogen concentrations over 45% by volume. The severe environment, stringent product and process requirements, and the fragility of partially-formed coatings limit the insertion of probes or instruments into the coater vessel during operation. Pressure instrumentation were installed on the gas inlet line and exhaust line of the 6-in. coater to monitor the bed differential pressure and internal pressure fluctuations emanating from the fuel bed as a result of bed and gas “bubble” movements. These instruments are external to the particle bed and provide a glimpse into the dynamics of fuel particle bed during the coating process and data that could be used to help ascertain the adequacy of fluidization and, potentially, the dominant fluidization regimes. Pressure fluctuation and differential pressure data are not presently useful as process control instruments, but data suggest a link between the pressure signal structure and some measurable product attributes that could be exploited to get an early estimate of the attribute values.
Uniformity Assessment of TRISO Fuel Particle Distribution in Spherical HTGR Fuel Element Using Voronoi Tessellation and Delaunay Triangulation
