Passage: The U.S. developed the Girdler sulfide chemical exchange production process—which was first demonstrated on a large scale at the Dana, Indiana plant in 1945 and at the Savannah River Plant, South Carolina in 1952. DuPont operated the SRP for the USDOE until 1 April 1989, when Westinghouse took it over.

Question: When did Dupont operate until for the USDOE?
1 April 1989