Core-catcher concept is widely used as a mitigation measure for containment protection under severe accident condition. Preliminary design of core-catcher is combined with ex-vessel corium behavior and corium cooling. The loose coupling of THEMA and RELAP codes provides a convenient method to evaluation the coolability of core catcher with a realistic ex-vessel corium characteristic by couple the corium and concrete basemat parameters like spreading area heat flux and etc. calculated by THEMA code and thermal-hydraulic transient behavior of coolant which flows through the basemat and is calculated by RELAP. In this paper the calculation results of coupling methodology is compared with experiment result and simulation of finite element model. The calculation results are consistent to the BENSON test rig, which demonstrates the heat removing capability of EPR core-catcher. However, it also reveals the flow instability in coolant channel, which penalizes the core-catcher coolability. But with an improved design of core-catcher with pre-filling water and core-catcher seal, which we presented in this paper, effect of flow instability can be mitigated, especially for the inlet and outlet of coolant channel.

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