Construction began in 1957, and the first low-energy reactor, ZENITH, was completed and in operation by the end of 1959. The site did not officially open until 16 September 1960. This was quickly followed by two new reactors, NESTOR in 1961 and DIMPLE in 1962. Many others followed. Cockcroft also suggested that larger fusion reactors be built at Winfrith, but this was met by serious pushback from the scientists involved in the program. This work instead moved to today's Culham Centre for Fusion Energy.