Many countries are relying on nuclear power as a vital part of their energy mix. At least 60 new nuclear power stations are being built or planned world-wide. But the disaster in Japan has raised awareness of the risks posed by the technology.The situation shows that even today, after decades of operating atomic power plants, unforeseen events can cause problems that have not been anticipated in safety plans. Scientists at the Institute of Energy and Climate Research in Jülich have long been exploring the issues surrounding nuclear safety. One thing they have done is simulate the synthesis of hydrogen within reactors. It is a risk that became a reality at the Fukushima power plant.