ATHLET CD

       The ECORE module consists of models for fuel rods, control rods (Ag, In, Cd and B4C) and fuel element channels. The module describes the mechanical fuel rod behavior (ballooning), the oxidation of zirconium and boron carbide, dissolution of fuel by zirconium and of boron carbide by steel, as well as melting of metallic and ceramic components. The model takes into account oxidation, freezing, re-melting, re-freezing and the formation and dissolution of blockages. Steam consumption and hydrogen generation by oxidation and the flow blockage are taken into account in the fluid dynamics model. Besides the convective heat transfer, modelling also covers the heat radiation between the fuel rods and the surrounding core structures. The FIPREM module describes the release of fission products and aerosols. Transport and retention of aerosols and fission products in the coolant system are simulated by the SOPHAEROS code, developed by the Institut de Radioprotection et de Sûreté Nucléaire (IRSN).

      The module MEWA for simulation of the debris bed has already been implemented in ATHLET-CD. It has its own fluid dynamics for the flow in porous media and is coupled to the ATHLET fluid dynamics on the outer boundaries. The transition of the nearly intact core geometry (ECORE) to debris bed (MEWA) depends on the local degree of core degradation.

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