Reactor systems having an external fuel salt loop

A nuclear reactor system comprising:

• a vessel encompassing a reactor core, the reactor core configured to receive molten fuel and achieve criticality of the molten fuel via fission therein, the vessel comprising a vessel exterior surface;
• an external loop line external to the vessel and comprising a loop line exterior surface, the external loop line being:
• configured to circulate molten fuel;
• fluidly coupled to a bottom portion of the vessel at a first end of the external loop line;
• fluidly coupled to an upper portion of the vessel above the reactor core at a second end of the external loop line;
• and
• configured to:
• receive the molten fuel from the vessel at the first end;
• allow the molten fuel to circulate through the external loop line;
• and
• allow the molten fuel to return to the vessel at the second end;
• a pump configured to circulate the molten fuel through the reactor core and through the external loop line;
• one or more heaters external to the vessel and configured to provide heat to at least a portion of the loop line external surface and at least a portion of the vessel exterior surface;
• and
• a neutron reflector encompassing the vessel exterior surface, wherein the neutron reflector is heated by the one or more heaters.