The concept that useful energy could be extracted from the atom began with the discovery of radioactivity in the early 1900's. The discovery of fission in 1939 and subsequent development of potential chain reaction models culminated with the achievement of the first chain reacting system in 1942 14 . Nuclear development efforts then went forward in parallel towards the construction of nuclear weapons and nuclear reactors for the production of plutonium and plants to produce highly enriched uranium. Initial operation of the production reactors at Hanford, Washington, occurred in 1944. These initial production reactors were light water cooled and graphite moderated. Additional production reactors constructed at the Savannah River plant in South Carolina were heavy water cooled and heavy water moderated.