Empirical and Mechanistic Transient Fission Gas Release Model for High-Burnup LOCA Conditions

In response to the nuclear industry desire extend burnup beyond current licensing practices, US Nuclear Regulatory Commission (NRC) released a research information letter (RIL) that provides basis for analyzing fuel fragmentation, relocation, and dispersal (FFRD) in light-water reactors. Of five elements discussed, most ambiguous is significance of transient fission gas (FG) release (FGR) (tFGR) its effects on performance under loss-of-coolant accident conditions. fresh fuel, FG migration eventual primarily governed by diffusion-based mechanisms at higher temperatures (>1,000°C). However, governing FGR changes as increases. More recent indicates increases increases, specifically temperature conditions, this occurs lower with new mechanism. This behavior has been attributed microcracking likely related microstructure embrittlement presence over pressurized bubbles. The NRC RIL outlines complexity phenomenon need deeper understanding adequately address FFRD regulatory application. Therefore, manuscript intends summarize publicly available tFGR data discuss observed dependencies (e.g., burnup, heating rate, sample geometry, terminal temperature). An empirical model developed benchmarked against recently published experimental data. limited conditions which fitting exist and, therefore, high-level discussion included provide roadmap atomistically-informed multiscale modeling conjunction collection develop mechanistic widely applicable broad range high burnup.