b'A high-speed, fiber-based pyrometer has been developed, tested, and deployed in the Transient Reactor Test (TREAT) facility for use in fueled experiments to provide accurate high temperature measurements.conducted by inserting an opticalas Accident Tolerant Fuel - Separate fiber into a titanium tube which wasEffects Test Holder (ATF-SETH). This inserted into the air coolant chan- experiment series used two pyrom-nels between fuel elements in TREAT.eters per capsule viewing the clad-From this preliminary testing, theding surface of a fuel rodlet. These impact of radiation induced emis- pyrometers successfully measured sion and attenuation on pyrometertemperatures ranging from ~400 C performance has been evaluated.to ~2100 C throughout this experi-Through this opportunity techniquesment series. These measured temper-have been developed to account foratures were used for calorimetry to the radiation-induced emission inobtain the power coupling factor the measured spectrum to minimizebetween the TREAT driver fuel and its impact on low-temperature,the fuel rodlet in the experiment. high-flux conditions. For most high- The power coupling factor measured temperature applications the radia- with this technique was confirmed tion-induced emission is negligiblewith alternative methods. This test compared to the thermal emission,series represented the first successful which has been successfully demon- pyrometry measurements for an strated. Following this preliminaryin-pile fueled experiment.in-pile testing, the fiber optic-based pyrometer was deployed in the fueled TREAT experiment series referred to 2019|AFC ACCOMPLISHMENTS 121'