the b reactor had its first nuclear chain reaction in september, 1944, the d reactor in december 1944 and the f reactor in february 1945. the reactor produced plutonium-239 by irradiating uranium-238 with neutrons generated by the nuclear reaction. it was one of three reactors – along with the d and f reactors – built about six miles (10 km) apart on the south bank of the columbia river. each reactor had its own auxiliary facilities that included a river pump house, large storage and settling basins, a filtration plant, large motor-driven pumps for delivering water to the face of the pile, and facilities for emergency cooling in case of a power failure.