Swiss voters are casting their ballots to decide whether or not to speed up the process of phasing out the country's nuclear power plants. <br/><br/>If voters choose "yes" in today's referendum, it would force three of the country's five reactors to close next year, and the remaining two by 2029. <br/><br/>The five plants currently generate 40 per cent of Switzerland's electricity. Polls suggest a tight race on the issue, which is being championed by environmentalists. <br/><br/>The Swiss Greens and Social Democrats have been pressing for a vote since the Fukushima disaster in Japan in 2011, arguing that Swiss plants are ageing and unsafe.