The behavior of pellet-cladding gap is very complex, which includes many physical phenomena, such as the change of gap size caused by pellet swelling and cladding creep, the change of gap gas composition caused by fission gas release, and the change of thermal conductivity of single component and multi-component gas.

Pellet-cladding gap heat transfer coefficient is a key parameter for safety analysis, which directly affects the thermal-mechanical performance of fuel rods under different conditions. Among them, pellet-cladding gap is the key parameter affecting pellet-cladding gap heat transfer. Because the roughness of the outer surface of the pellet and the inner surface of the cladding directly affects the size of the gap, it is necessary to conduct in-depth research on it.

The research on the influence of pellet and cladding roughness on pellet-cladding gap heat transfer focuses on the experimental study and model building, but seldom on the influence of the irradiation process in the fuel reactor.

On the basis of studying the steady-state and transient operation of fuel rods and the influence of roughness on various gap heat transfer modes, the influence law and mechanism of roughness on pellet-cladding gap heat transfer are discussed, which has guiding significance for the design of new fuel rods.

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