Impact of gap size uncertainty on calculated temperature uncertainty for the advanced gas reactor experiments

Research being conducted on tristructural-isotropic fuel development and qualification involves seven advanced gas reactor (AGR) experiments that were planned to provide fuel qualification data to support the licensing and operation of the high-temperature gas-cooled reactor. Each AGR test consists of multiple independent capsules containing fuel compacts placed in one or more graphite cylinders shrouded by a stainless-steel shell. These capsules are instrumented with thermocouples embedded in the graphite holder, enabling temperature control. The desired fuel temperature is maintained by variation of the neon/helium gas mixture in response to feedback from thermocouple readings. In the absence of direct measurements, the commercial finite-element heat transfer code ABAQUS was used to predict fuel temperatures. Recognizing inherent uncertainties in the simulation model due to complex physical mechanisms, capsule geometries, and material properties, comprehensive temperature uncertainty quantification was performed. The uncertainty results reveal that the uncertainties in gap sizes are among the most influential factors contributing to calculated temperature uncertainty. The gap size uncertainties originate from a lack of direct experimental data for accurate assessment of dimensional change rates of fuel compacts and graphite components due to complex irradiation-induced material shrinkage or swelling. The study described here focuses on the impact of the gap size uncertainties based on the post-irradiation examination metrology data on calculated temperature uncertainty.