An economic and mathematical model has been developed to determine the competitiveness of REMIX-A and -C uranium-plutonium fuel obtained by reprocessing spent fuel from thermal reactors. The presented model makes it possible to calculate the cost metrics of nuclear fuel components and the fuel component of the cost of NPP electricity as a function of the cost metrics of key process changeovers. It is shown that as the market quotations for natural uranium and separation work increase, REMIX fuel becomes more competitive and, more importantly, all the more significant, the lower the cost of reprocessing spent fuel. However, even with zero cost of reprocessing the gain from the introduction of REMIX fuel does not exceed 25%. At the same time, its use allows a 20-fold reduction in the mass of radioactive waste going to final disposal, 24% (REMIX-A) to 36% (REMIX-C) savings of natural uranium, and 8–18% of separation work (REMIX-A) as well as 18% (REMIX-A) to 40% (REMIX-C) reduction in the accumulation of depleted uranium hexafluoride.