Nuclear power generation system and nuclear reactor unit

A nuclear reactor unit, comprising:

• a reactor core fuel;
• a nuclear reactor vessel that
• surrounds the reactor core fuel;
• and
• shields a space located inside of the nuclear reactor vessel in which the reactor core fuel is present to shield radioactive rays;
• and
• a heat conductor through which heat from the space is transferred to an outside of the nuclear reactor unit by solid heat conduction, wherein
• the heat conductor includes a first heat conductor and a second heat conductor, wherein the second heat conductor has a higher thermal conductivity than a thermal conductivity of the first heat conductor,
• the first heat conductor has:
• a first face exposed to the inside of the nuclear reactor vessel and flush with an inner surface of the nuclear reactor vessel, the first face forming a part of the inner surface of the nuclear reactor vessel such that the heat conductor and the reactor vessel share the first face;
• and
• a second face exposed to outside of the nuclear reactor vessel and flush with an outer surface of the nuclear reactor vessel, the second face forming a part of the outer surface of the nuclear reactor vessel such that the first heat conductor and the nuclear reactor vessel share the second face,
• the second heat conductor is disposed outside the nuclear reactor vessel and is in contact with the second face of the first heat conductor,
• the first and second heat conductors are both solid, and
• the first heat conductor has a thickness equal to a thickness of the nuclear reactor vessel.