An exemplary embodiment can include an apparatus including: an internal-external hybrid nuclear reactor, which can include: at least one reciprocating internal engine; and at least one external reactor integrated with said at least one reciprocating internal engine. The reciprocating engine can receive nanofuel (including moderator, nanoscale molecular dimensions & molecular mixture) internally in an internal combustion engine that releases nuclear energy. A method of operating the hybrid nuclear reactor can include operating the reciprocating internal engine loaded with nanofuel in spark or compression ignition mode. A method of cycling the reciprocating internal engine, can include compressing nanofuel; igniting nanofuel; capturing energy released in nanofuel, which is also the working fluid; and using the working fluid to perform mechanical work or generate heat.

An exemplary embodiment can include an apparatus including: an internal-external hybrid nuclear reactor, which can include: at least one reciprocating internal engine; and at least one external reactor integrated with said at least one reciprocating internal engine. The reciprocating engine can receive nanofuel (including moderator, nanoscale molecular dimensions & molecular mixture) internally in an internal combustion engine that releases nuclear energy. A method of operating the hybrid nuclear reactor can include operating the reciprocating internal engine loaded with nanofuel in spark or compression ignition mode. A method of cycling the reciprocating internal engine, can include compressing nanofuel; igniting nanofuel; capturing energy released in nanofuel, which is also the working fluid; and using the working fluid to perform mechanical work or generate heat.