2017 | AFC ACCOMPLISHMENTS 101 The postirradiation examination of ATF-1 represents the first results from the collaboration of industry and DOE to research new fuels to enhance the accident tolerance of current commercial light water reactors. combination to various different burnups.The small fuel rods are encapsulated to prevent release into the ATR primary coolant in the event of a cladding breach.To date, UO2 plus additives clad in Zircaloy-4 (AREVA concepts) and U3Si2 clad in Zirlo have been examined postir- radiation.The linear heat generation rate is set by varying enrichment and axial location of rodlets in the irradiation positions.The temperature on the cladding surface is controlled by the gap between the cladding and the capsule.This configuration approximates light water reactor irradiation conditions inside the fuel pin so that fuel behavior and fuel- cladding interactions can be evalu- ated.The results of these screening irradiations support the development of new fuel forms to help light water reactors potentially operate with enhanced safety margins. PIE of these concepts consists of several different examinations that are used to deter- mine different fuel performance properties such as fuel swelling, cracking, fission product distribution, burnup, radiation induced dimension changes, changes in microstructure, and fuel-cladding interactions. Accomplishments: Baseline PIE was completed on 3 ATF-1 rodlets from the AREVA concept that tested UO2 with several addi- tives that are expected to enhance the thermal conductivity of UO2. These samples are now available for additional PIE exams as desired by the vendor sponsor. Neutron radiography, gamma spectrometry that reveals fission product distribution, dimen- sional inspections, fission gas release data, burnup analysis, and optical microscopy has been produced for these samples.An example of optical microscopy performed on ATF-1A R1 (UO2-Zircaloy) is shown below. As expected at this low burnup there is no contact between the fuel and the Zircaloy.The fission gas bubble morphology changes radially in the fuel pin as the local irradiation temperature increases towards the center of the fuel pin.This sort of microstructure is very valuable for