Molten fuel reactor thermal management configurations

A molten salt nuclear reactor comprising:

• a substantially frustum-shaped reactor core containing a fissionable fuel salt and having a reactor core bottom and a reactor core top, the reactor core bottom being larger than the reactor core top, the reactor core having a heated fuel salt outlet, a cooled fuel salt inlet, and a thermal center above the cooled fuel salt inlet;
• at least one heat exchanger that receives heated fuel salt at a heat exchanger fuel salt inlet below the reactor core's heated fuel salt outlet, transfers heat from the fuel salt to a coolant, and discharges the cooled fuel salt at a heat exchanger fuel salt outlet fluidly connected to the reactor core's cooled fuel salt inlet;
• and
• wherein the thermal center of the reactor core is at a level below the heat exchanger fuel salt outlet;
• and
• wherein the location of the thermal center causes natural circulation in the case of a loss of forced flow while the reactor is in a state of criticality.