Chemical behavior of fission products is predicted for a “dynamic core” fast reactor, where the fuel is pumped through an outside loop by the coolant. For a 7.5 at % Pu/25 at % Co/67.5 at % Ce alloy, the various fission products are classified as sodium-extractable, fuel-soluble, precipitating, and rare gases. Evidence predicting the behavior of each class is presented. The rates of extraction of removable fission products are estimated for different modes of operation. Extractable fission product atoms are expected to remain in the fuel phase for only a few seconds. Sixty percent of all of the fission product atoms formed remain in solution in the fuel phase, and occupy a volume (∼35% of that of all fission products) roughly equal to that of the Pu consumed. The consumption of the initial inventory of Pu would require the gradual addition of 110% of the original amount of Pu, of which 3% is required to compensate for poisoning. The effective chemical composition of the fuel would be little changed during “100% burn-up.” A dynamic-core fast reactor can be operated for several years as a continuous chemical system at an economic burn-up rate.