Patent Number: 
Section: claims

1. A method for removing heat from a molten fuel nuclear reactor having a reactor core containing high temperature liquid nuclear fuel, the method comprising:delivering lower temperature nuclear fuel into the reactor core, therebydisplacing some high temperature nuclear fuel from the reactor core upward into a first heat exchanger anddisplacing some nuclear fuel downward in a second heat exchanger,wherein the first heat exchanger is arranged above and in fluid communication with the reactor core to receive nuclear fuel from the reactor core,wherein the second heat exchanger is arranged above the reactor core and in fluid communication with both the first heat exchanger and the reactor core to receive nuclear fuel from the first heat exchanger and to deliver nuclear fuel to the reactor core,wherein the first heat exchanger comprises a shell-and-tube heat exchanger and the second heat exchanger comprises a separate shell-and-tube heat exchanger; androuting coolant through the first and second heat exchangers, therebytransferring heat from the high temperature nuclear fuel to the coolant andconverting the displaced high temperature nuclear fuel into the lower temperature nuclear fuel. 2. The method of claim 1, wherein delivering the lower temperature nuclear fuel into the reactor core includes passing the lower temperature nuclear fuel from the second heat exchanger into the reactor core. 3. The method of claim 1, wherein delivering the lower temperature nuclear fuel includes operating at least one impeller to drive flow of the nuclear fuel through the first and second heat exchangers. 4. The method of claim 1 further comprising:neutronically shielding the first and second heat exchangers from neutrons generated in the reactor core. 5. The method of claim 1, wherein routing the coolant includes delivering coolant at a temperature less than that of the high temperature nuclear fuel to the second heat exchanger. 6. The method of claim 1, wherein routing coolant includes pumping coolant first through the second heat exchanger and then through the first heat exchanger. 7. The method of claim 1, wherein the first and second heat exchangers are vertically-oriented shell-and-tube heat exchangers located above the reactor core.