Fission reaction control in a molten salt reactor

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;
• and
• a 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.