As in many industrialised countries, nuclear power in Germany was first developed in the late 1950s. Only a few experimental reactors went online before 1960, and an experimental nuclear power station in Kahl am Main opened in 1960. All of the German nuclear power plants that opened between 1960 and 1970 had a power output of less than 1,000 MW and have now all closed down. The first commercial nuclear power plant started operating in 1969. Obrigheim, the first grid station, operated until 2005. (Neckarwestheim.) A closed nuclear fuel cycle was planned, starting with mining operations in the Saarland and the Schwarzwald; uranium ore concentration, fuel rod filling production in Hanau; and reprocessing of the spent fuel in the never-built nuclear fuel reprocessing plant at Wackersdorf. The radioactive waste was intended to be stored in a deep geological repository, as part of the Gorleben long-term storage project.

When did germany build its first nuclear power plant? Okie... think carefully first, then make a decision:
The relevant information to answer the above question is: Only a few experimental reactors went online before 1960, and an experimental nuclear power station in Kahl am Main opened in 1960. So, the answer is 1960.