2, Los Alamos National Laboratory, Los Alamos, New Mexico, United States
Over the lifetime of the Transient Reactor Test Facility (TREAT) reactor from 1959 to 1994, a series of historical tests disclosed certain material specific requisites for irradiation testing variables resulted in negligible structural damage after exposure to the reactor and multiple experiments. Comparable fuel design, material testing, and qualifications needs to occur for the high-enriched uranium (HEU) to low enriched uranium (LEU) fuel conversion (<20% U235) of TREAT. This includes, retaining a uniform precipitate dispersion of fueled UO2 micron-size particles throughout a graphite-moderating matrix, where high-density graphite is in direct contact with the fuel and acts as a moderator. On that note, the design of future LEU reactor TREAT fuel core will consider the relative sizing and spacing of fuel as well as the retention of graphite in accordance with the expected thermal, neutron, and energy portfolio for future conversion. In light of the above, LEU conversion fuel blocks currently being manufactured must undergo critical materials testing, irradiation, and examination to determine effects on the manufactured replacement fuel blocks at the millimeter to sub-micron size scale.
Herein, we will report and update the community on value-added studies focusing on the reported particle size distributions of fabricated surrogate and fueled fuel blocks using non-destructive X-ray micron tomography (µCT) and electron-based microscopy. The developed computational image analysis methods to support this effort has included the development of techniques to distill 3-D particle-size distributions, nearest neighbor distances, volume fraction particle curves, and full reconstructions from µCT tomography considered as Big Data spanning thousands of images and several hundreds of terabytes. At this point, the current and pending results provide methodologies to qualify replacement fuel blocks as well as support decisions regarding the final fabrication specifications and tolerances associated with the replacement TREAT fuel assembly and final block configuration.