2018 | AFC ACCOMPLISHMENTS 156 burnup was 7.6 atomic % heavy metal. Neutron radiography of the examined pin (see Figure 1) revealed typical metallic fuel behavior for this burnup.The fuel appears to have swelled radially to fill the cladding, the axial swelling of 1.8% is in line with expectations, and a small amount of fuel is dissolved into the sodium at the top of the fuel column. Gamma spectrometry also revealed prototypic behavior. In addition to axial gamma spectrometry scans, tomographic gamma spectrometry scans were performed that revealed the Cs-137 distribution at mid-plane.This is shown in Figure 2, and reveals that some of the Cs is located in the interior of the fuel while the majority is located on the periphery near the inner cladding.The black lines in Figure 2 represent the location of the cladding in the tomographic scans. Cesium is often observed to travel dissolved in the sodium.The Cs signal from the center of the fuel pin may be an indication of sodium occupying some of the porosity in the fuel. This is sometimes known as sodium logging and is a poorly understood but significant performance effect in metallic fuel. Further research into this sort of Cs signal is planned to better understand if this technique can further illuminate the sodium logging phenomenon. Optical microscopy taken from the center of the fuel stack at the same location as the gamma tomography is shown in Figure 3.The location of large porosity in this cross section generally corresponds to the location of Cs-137 in the gamma tomography. Constituent redistribution at this location is not as pronounced as often shown in literature for U-Pu-Zr metallic fuel, but the central region does show evidence of Zr migrating towards the center of the fuel and a phase change.This can be seen in the central area of Figure 3 stretching out in a radius of about 250┬Ám from the center of the fuel cross section.These exams generally show good performance for this alloy and that there is little to no detrimental effects from the addition of americium to this fuel. However, electron microscopy is needed to characterize this fuel system more fully at the micro scale and determine the location of Am in the fuel.This is planned for next year. Characterization of EBR-II legacy fuel pins is of paramount importance in order to assess the applicability of using ATR testing to evaluate transmutation fuel performance.