Numerical investigations on the melting process of the nuclear fuel rod in RIAs and LOCAs

In light water reactor, melting of nuclear fuel rod (NFR) is critical. Therefore, this issue needs to be simulated and analyzed with different accidental conditions. In this paper, one-dimensional model is build and used to simulate the melting process of NFR in nuclear core. The numerical model includes three regions; these are Uranium dioxide fuel pellet, Helium layer and Zirconium alloy cladding. Due to huge temperature gradient in radial direction of NFR, material properties which include specific heat, thermal conductivity and density are non-linear and depends on temperature. In addition to this the convection and radiation heat transfer are also considered in the Helium layer region. To solve the enthalpy formulation of melting process, the Half Boundary Method (HBM) is used in this paper. The HBM is accurate, efficient and save calculational memory. The melting process of fuel rod is simulated during Reactivity-Initiated Accidents (RIAs) and Loss-Of-Coolant Accidents (LOCAs). The results showed us that if RIA happens melting will first take place at the center of pellet and in case of LOCA, melting will begin inside cladding.