A self-diagnosing and accident-handling unmanned nuclear reactor, comprising a nuclear reactor driving system configured to include a nuclear reactor vessel accommodating a nuclear reactor core and a steam generator to which a steam pipe and a water supply pipe are connected; and a nuclear reactor safety system configured to be divided into an energy release space that accommodates the nuclear reactor driving system, an energy absorbing space that communicates with the energy release space through a passage formed thereover and accommodates a coolant, and an energy transfer space that isolates from the energy release space and the energy absorbing space and has a residual heat removing portion connected to the nuclear reactor driving system and a flow path connected to the energy absorbing space provided therein to transfer heat released from the nuclear reactor driving system to the coolant and transfer the heat absorbed into the coolant to the outside to be discarded, wherein the residual heat removing portion includes a heat exchange portion adapted to transfer heat by a two-phase heat transfer mechanism using the coolant supplied by the flow path connected to the energy absorbing space, an airtight container portion that has the coolant and the heat exchange portion accommodated therein and has a lower part opened to distribute the coolant, and an outer cylinder portion that is provided to surround the airtight container portion to accommodate and distribute the coolant, and a space having a saturated steam pressure and being formed at a position where the heat exchange portion is disposed in the airtight container portion by a coolant steam which is generated by being boiled by the heat exchange portion, wherein the heat exchange portion includes a primary heat exchanger that is connected to the nuclear reactor driving system to distribute the coolant circulated through the nuclear reactor driving system and a secondary heat exchanger that is disposed to be close to the primary heat exchanger to absorb heat from the coolant distributed within the primary heat exchanger, wherein the coolant steam that forms the space having the saturated steam pressure at a position where the heat exchange portion is disposed in the airtight container portion is generated by being boiled by the primary heat exchanger, and wherein the coolant supplied by the flow path connected to the energy absorbing space on the space having the saturated steam pressure is sprayed to the primary heat exchanger and the secondary heat exchanger to take place the two-phase heat transfer mechanism. a nuclear reactor driving system configured to include a nuclear reactor vessel accommodating a nuclear reactor core and a steam generator to which a steam pipe and a water supply pipe are connected; and a nuclear reactor safety system configured to be divided into an energy release space that accommodates the nuclear reactor driving system, an energy absorbing space that communicates with the energy release space through a passage formed thereover and accommodates a coolant, and an energy transfer space that isolates from the energy release space and the energy absorbing space and has a residual heat removing portion connected to the nuclear reactor driving system and a flow path connected to the energy absorbing space provided therein to transfer heat released from the nuclear reactor driving system to the coolant and transfer the heat absorbed into the coolant to the outside to be discarded, wherein the residual heat removing portion includes a heat exchange portion adapted to transfer heat by a two-phase heat transfer mechanism using the coolant supplied by the flow path connected to the energy absorbing space, an airtight container portion that has the coolant and the heat exchange portion accommodated therein and has a lower part opened to distribute the coolant, and an outer cylinder portion that is provided to surround the airtight container portion to accommodate and distribute the coolant, and a space having a saturated steam pressure and being formed at a position where the heat exchange portion is disposed in the airtight container portion by a coolant steam which is generated by being boiled by the heat exchange portion, wherein the heat exchange portion includes a primary heat exchanger that is connected to the nuclear reactor driving system to distribute the coolant circulated through the nuclear reactor driving system and a secondary heat exchanger that is disposed to be close to the primary heat exchanger to absorb heat from the coolant distributed within the primary heat exchanger, wherein the coolant steam that forms the space having the saturated steam pressure at a position where the heat exchange portion is disposed in the airtight container portion is generated by being boiled by the primary heat exchanger, and wherein the coolant supplied by the flow path connected to the energy absorbing space on the space having the saturated steam pressure is sprayed to the primary heat exchanger and the secondary heat exchanger to take place the two-phase heat transfer mechanism.