The Pacific Northwest National Laboratory (PNNL) is currently developing a novel spherical fuel element concept that offers low fuel temperatures, low stored energy, and long core life. Fuel performance modeling has been conducted using the PNNL-developed Atoms for Peace Reactor (AFPR)-100 as a platform for demonstrating the potential of the fuel element concept. The AFPR-100 is a small [100-MW(electric), 300-MW(thermal)], water-cooled reactor concept that is designed to use established technology, be passively safe, and be proliferation resistant. The fuel performance modeling has demonstrated that this fuel element has a short thermal time constant, has low fuel temperature, provides a barrier for retention of fission products, and will have long-term dimensional stability.
A technique for manufacturing these fuel elements was developed. A fabrication demonstration was conducted in cooperation with a commercial vendor to evaluate the feasibility of manufacturing the fuel elements. In order to demonstrate the proposed technique, the proposed spherical elements were produced using existing processes that could be scaled to large batch sizes. Surrogate ZrO2 kernels were substituted for the fuel in this demonstration. Thorough characterization of the fuel elements was performed at various stages in the fabrication process. The metallographic characterization included electron microscopic analysis of coating microstructure, and particular attention was paid to interface regions to search for deleterious reaction zones, debonding, and porosity. Although this demonstration is not complete, early results are promising and will be discussed in this paper.
This paper will describe the fuel element, show the results of fuel performance calculations for this element, describe the proposed fabrication process, and discuss the results of a fabrication demonstration to date that has been performed for this concept.