Patent Number: 
Section: claims

1. A fast spectrum molten salt reactor comprising:one or more heat exchangers;an unmoderated nuclear reactor core configured to contain a volume of molten fuel salt of sufficient size to establish criticality due to the production of fast neutrons within the volume;a primary coolant system configured to circulate a molten fuel salt-coolant mixture between the unmoderated nuclear reactor core and the one or more heat exchangers; anda molten fuel salt exchange system, the molten fuel salt exchange system being configured to reduce reactivity of the fast spectrum molten salt reactor by replacing a selected volume of the molten fuel salt-coolant mixture with a selected volume of feed material when a parameter indicative of reactivity of the molten salt reactor indicates that the reactivity has increased above an upper threshold defining a maximum reactivity,wherein the molten fuel salt exchange system is fluidically coupled to the nuclear reactor core and configured to exchange the selected volume of the molten fuel salt-coolant mixture with the selected volume of feed material containing a mixture of a selected fertile material and a carrier salt,wherein the feed material does not contain any fissile material,wherein the molten fuel salt exchange system is configured to control a composition of UCl3—UCl4—NaCl as a whole in a fast spectrum fission reaction by exchanging the feed material with the selected volume of the molten fuel salt-coolant mixture in the nuclear reactor core. 2. The fast spectrum molten salt reactor of claim 1 wherein the molten fuel salt exchange system includes a feed-fuel supply unit configured to transfer the feed material into the molten fuel salt-coolant mixture circulating through the nuclear reactor core. 3. The fast spectrum molten salt reactor of claim 1 wherein the molten fuel salt exchange system includes a feed-fuel supply unit configured to transfer the selected volume of the feed material into the molten fuel salt-coolant mixture circulating through the nuclear reactor core. 4. The fast spectrum molten salt reactor of claim 1 wherein the molten fuel salt exchange system includes a feed-fuel supply unit configured to transfer a selected composition of the feed material into the nuclear reactor core. 5. The fast spectrum molten salt reactor of claim 1 wherein the molten fuel salt exchange system includes a used-fuel transfer unit configured to transfer the selected volume of the molten fuel salt-coolant mixture as used-fuel from the nuclear reactor core. 6. The fast spectrum molten salt reactor of claim 1 wherein the molten fuel salt exchange system is configured to transfer concurrently the selected volume of the molten fuel salt from the nuclear reactor core and the feed material into the nuclear reactor core. 7. The fast spectrum molten salt reactor of claim 1 wherein the molten fuel salt exchange system is configured to control the reactivity of the fast spectrum molten salt reactor by exchanging the feed material with the selected volume of the molten fuel salt-coolant mixture in the nuclear reactor core. 8. The fast spectrum molten salt reactor of claim 1 wherein the molten fuel salt exchange system is configured to control the composition of the molten fuel salt-coolant mixture in the nuclear fission reaction by exchanging the feed material with the selected volume of the molten fuel salt-coolant mixture in the nuclear reactor core. 9. The fast spectrum molten salt reactor of claim 1 wherein the molten fuel salt exchange system is configured to exchange repeatedly the selected volume of the molten fuel salt-coolant mixture with the selected volume of the feed material to maintain the parameter indicative of reactivity of the molten salt reactor within a selected range of nominal reactivity over time. 10. The fast spectrum molten salt reactor of claim 1 wherein the molten fuel salt exchange system further includes a volumetric displacement control system having one or more volumetric displacement assemblies insertable into the nuclear reactor core, each volumetric displacement assembly being configured to volumetrically displace at least some of the molten fuel salt-coolant mixture from the nuclear reactor core when inserted into the nuclear reactor core. 11. The fast spectrum molten salt reactor of claim 1 wherein the molten fuel salt exchange system includes a volumetric displacement control system having one or more volumetric displacement bodies insertable into the nuclear reactor core, each volumetric displacement body being configured to volumetrically displace at least some of the molten fuel salt-coolant mixture from the nuclear reactor core when inserted into the nuclear reactor core. 12. The fast spectrum molten salt reactor of claim 1 wherein the molten fuel salt exchange system further includes a volumetric displacement control system having one or more volumetric displacement bodies insertable into the nuclear reactor core, each volumetric displacement body being configured to volumetrically displace at least some of the molten fuel salt-coolant mixture from the nuclear reactor core when inserted into the nuclear reactor core, the volumetric displacement control system further having a molten fuel salt spill-over system configured to transport the molten fuel salt-coolant mixture that is displaced by the volumetric displacement body above a tolerated fill level of the nuclear reactor core. 13. The fast spectrum molten salt reactor of claim 1 wherein the molten fuel salt exchange system further includes a volumetric displacement control system having one or more volumetric displacement bodies insertable into the nuclear reactor core, each volumetric displacement body being configured to volumetrically displace at least some of the molten fuel salt-coolant mixture from the nuclear reactor core when inserted into the nuclear reactor core, one or more volumetric displacement bodies being insertable at multiple insertion depths into the nuclear reactor core to maintain the parameter indicative of reactivity of the molten salt reactor within a selected range of nominal reactivity over time. 14. The fast spectrum molten salt reactor of claim 12, wherein the spill-over system includes a reservoir configured to receive the molten fuel salt-coolant mixture that is displaced by the volumetric displacement body above a tolerated fill level of the nuclear reactor core. 15. The fast spectrum molten salt reactor of claim 1, wherein the molten fuel salt exchange system removes molten fuel salt directly from the nuclear reactor core. 16. The fast spectrum molten salt reactor of claim 1, wherein the molten fuel salt exchange system delivers feed material directly into the nuclear reactor core. 17. The fast spectrum molten salt reactor of claim 1, further comprising:one or more reactivity parameter sensors configured to monitor the reactivity of the fast spectrum molten salt reactor. 18. The fast spectrum molten salt nuclear reactor of claim 17, wherein the one or more reactivity parameter sensors are selected from a fission detector, a neutron flux monitor, a neutron fluence sensor, a fission product sensor, a temperature sensor, a pressure sensor or a power sensor. 19. The fast spectrum molten salt reactor of claim 1, further comprising:a reactor containment vessel that encloses the one or more heat exchangers and the unmoderated nuclear reactor core. 20. The fast spectrum molten salt reactor of claim 1, further comprising:a feed material source containing feed material.