[en] The principle of the Defense in depth is essential in securing the safety of nuclear power plants, that is, to prevent cores-damaging severs accidents and to minimize the radiological consequences of the accidents 'as low as possible' (ALARA). One of the major design features of sodium fast reactors (SFRs) is that it has a large amount of sodium in the reactor vessel, providing a large heat capacity, such that it is feasible to contain the consequences of sever core damaging accidents in the vessel and primary system boundary. Containment of a severe accident in the primary system boundary, that is called in-vessel retention(IVR), is not a licensing requirement but set up as a design goal in most of the SFR design in the context of risk minimization. The objective of this report is to broadly review and compare the approaches and efforts made in the some of the major SFR designs of the US, Europe and Japan to prevent severe accidents and mitigate their consequences should they occur. Specifically, the subjects described in this report include design criteria or requirements, accident categorization and acceptance criteria, design features to prevent and contain severs accidents