Uranium-233 is a more efficient fuel in a thermalized flux than either 235U or 239Pu. Its nuclear performance and value to thermal converter reactors would be further enhanced if the 233U were produced free of 232U and if it were used to enrich natural or depleted uranium. Although it has been generally accepted that the fissile isotope produced in the blankets of the fast breeders will be Pu, clean 233U could be produced by charging thorium rather than 238U into the fast reactor blanket. Since the breeding gain does not appear significantly altered, the ultimate decision facing the breeding reactor operator will depend on the comparative revenue from the two fissile isotopes. The value of 233U will exceed that of Pu during early periods of breeding reactor development. As the value of Pu increases, due to fast reactor demand, the worth of 233U will also increase but at a slower rate. If the price of U3O8 is $12/lb, the worth of 233U will exceed that of Plutonium up to $22/g.