The UP3 plant start up has been achieved in two successive steps. The first one, from November 89 to April 90, involved all the facilities but T1, the head-end facility. During that period, shearing, dissolution and the first cycle extraction operations were performed in UP2 plant. 100 tons of fuel have been reprocessed that way. The second step began in August 1990, with the T1 facility start-up and the reprocessing of the resulting active solutions in the rest of the plant. This second phase involving the entire UP3 plant continued until the end of January 1991. At that time, 160 tons of fuel have been completely treated in UP3 plant.