###### Abstract
And the last type of cladding is Si/SiC cladding, which is the best among the three cladding materials in terms of its oxidation resistance and high-temperature strength; therefore, it has been called the ideal ATF cladding material [9]. Innovative fuel systems must be implemented to enhance fuel, plant work, and safety to meet or exceed design benchmark accidental conditions [11]. While current reactor designs predict the behavior of fission gases within fuel rods over their operational lifetime, current fuel designs are not able to compensate for over-lifetime gas release, and an extended burnup extent in existing reactors is a significant issue [12]. The behavior of gaseous fission products under irradiation conditions heavily impacts nuclear fuel rod performance [13]. The released fission gases access the rod's free space, which increases the internal pressure of the rod or creates bubbles, leading in fuel swelling and enhanced pellet cladding mechanical interactions (PCMIs). The above processes affect the mechanical behavior of rods [14], while the FGR reduces the thermal conductivity between the fuel and cladding. Gases within bubbles degrade the thermal conductivity of the fuel, ultimately influencing the temperature distribution of the fuel pellets. As a result [15], fission gases significantly affect the thermal properties of fuel rods. When fission gases enter bubbles, the fuel swells and mechanically interacts with the fuel cladding, closing the gap between the fuel and cladding. Fission gas release (FGR) causes the pressure in the rod free space to increase as well as causing the thermal conductivity of the rod filling gas to degrade. The safety of nuclear reactors and ultimate fuel repositories are assessed by utilizing nuclear fuel performance codes, with prediction for FGR being a crucial aspect. In fuel performance codes, FGR typically includes two steps [14]. First, based on the linear power rating, fission gas atoms are generated through fission reactions, and some of the gas atoms move to the grain boundaries via diffusion, with thermal diffusion during high temperatures being the primary form. In addition to thermally activated defects, irradiation-enhanced defect concentrations drive gas atoms to diffuse, with athermal diffusion under low temperatures being important. The released gas atoms are particularly relevant to the thermal conductivity of fuels with fast neutron factors, like nitride fuels, for which the release fraction at high temperatures may be lower than oxide fuels; however, the thermal conductance of the gap also deteriorates. Second, the concentration and release threshold of gas atoms causes the gas atoms to release and be stored on the grain boundaries. This behavior is affected by temperature and other properties. When analyzing the thermal-mechanical performance of fuel rods, fission gas behavior is a significant aspect, and this behavior is modeled by fuel performance codes. Modeling this behavior in nuclear fuels under irradiation involves accounting for various interactive phenomena. Gas atoms are produced inside fuel grains and diffuse towards grain bound aries. Bubbles precipitating and growing at the grain faces leads to fuel swelling. After bubble growth and interlink, the gas atoms release from the grain faces, causing thermal FGR. Gas atoms and the vacancy diffusion of bubbles contribute to the development of this process. Except for these diffusion ways, experiments have also justified that microcracking is mechanism of grain face separation, and gas atoms may be released from grain boundaries through these cracks, resulting in significant FGR in transient situations. These fast kinetics typically take a burst release into account. Under irradiation experiments, the FGR rate raises due to cracking on the grain boundaries, which is caused by fission gas accumulating and inducing thermal stresses.