###### Abstract
After transient heating, grain surfaces exhibit the phenomenon of planar separation, and the stored gas atoms release through the cracking along a particular area between two grains. Micro-cracking occurs at grain face causing grains unable to store gas atoms and thus leadin to additional fission gas release during transient situations [14]. According to [PERSON] et al. 2018, [16], fuel performance is affected by the amount and release of fission gases in UO\({}_{2}\) fuel, causing the fuel to swell and the gap pressure to increase. The majority of FGR undergoes three processes: first, gases are generated and move from bulk; second, bubbles in the grain face nucleate, grow, and interlink until they adhere to grain boundaries; third, gas atoms are transported through interlinkage grain boundary passages until they arrive at a free surface and are released. Gas atom diffusion primarily determines the above mechanisms, although knockout, recoil, and burst release may cause some gas atoms to release. As mentioned earlier, nuclear fuel performance is greatly affected by fission gas behavior. Moreover, fission gas behavior is related to the integrity and safety of nuclear power plants [17]. Indeed, the behavior of fission gases is of utmost importance in understanding and managing nuclear reactors, particularly in the context of nuclear accidents such as Chernobyl and Fukushima. In the case of Chernobyl, the accident was caused by a combination of design flaws, operator errors, and a rapid power excursion that led to a destructive steam explosion and a subsequent graphite fire. The release of fission products, including fission gases such as xenon and krypton, played a significant role in the dispersion of radioactive material into the atmosphere. Similarly, the Fukushima accident was triggered by a massive earthquake and tsunami that resulted in the loss of power and cooling capabilities at the Fukushima Daiichi nuclear power plant. The subsequent overheating and melting of fuel assemblies led to the release of fission gases and other radioactive materials into the environment. Studying the behavior of fission gases under severe accident conditions helps in assessing the consequences and developing strategies for mitigating their release and dispersal. Research on fission gas behavior encompasses various aspects, including gas release mechanisms, diffusion and transport within fuel materials, retention in fuel rods, and the potential effects on fuel performance and reactor safety. By gaining a deeper understanding of these factors, scientists and engineers can develop improved fuel designs, safety systems, and accident management strategies to enhance the overall safety and reliability of nuclear reactors. It is worth noting that significant advancements have been made in the field of fission gas behavior research over the years, contributing to the development of more robust and accident-tolerant fuel designs, improved reactor operation and maintenance practices, and enhanced safety measures in the nuclear industry. However, fission gas behaviour is very complicated, as it includes FGR, fission gas diffusion, grain growth, and swelling. On the other hand, different types of nuclear fuels may behave differently. It is relatively easy to simulate single fission gas behavior, such as FGR processes under steady state conditions, but this fails to reflect the thermal fission gas behaviour in the nuclear reactor. A more sophisticated fission gas behaviour model is strongly needed to better understand this phenomenon. UO\({}_{2}\) fuels have been successfully and broadly used as primary fuels in commercial light water reactors. The prediction of fission gas behaviour is important for fuel rod performance when a reactor operates at stable conditions. The fission gas is released when the gas reaches a saturation value in the grain boundaries. The fuel rod pressure and temperature continue to increase with gas release due to the degradation of gap thermal conductance between the pellet and cladding.