In March 2011, a devastating earthquake and tsunami in Japan caused a meltdown at the Fukushima nuclear power plant.

As tens of thousands of people were evacuated from nearby towns and villages, the world waited anxiously to see whether the radioactive fallout would spread across the country, or even be carried overseas.

Unsurprisingly, in the wake of this incident, the nuclear operations of other countries have come under considerable scrutiny.

One such country is the US where more than 100 similar reactors - some of them in earthquake zones or close to major cities - are now reaching the end of their working lives.

Their owners want to keep them running, but others - from environmentalists to mainstream politicians - are deeply concerned.

In this investigation for People & Power, Joe Rubin and Serene Fang of the Center for Investigative Reporting examine whether important safety considerations are being taken into account as the US Nuclear Regulatory Commission (NRC) considers extending the licences of these plants.

The agency has recently come under fire for glossing over the potential dangers of ageing reactors, for becoming too cosy with the industry and for political infighting among the agency's senior executives, which critics in the US Senate and elsewhere say seriously hampers its ability to ensure safety.

The investigation focuses on the Pacific Gas & Electric nuclear facility at Diablo Canyon and two others, Vermont Yankee and Indian Point in New York.

These three sites represent the dangers posed to nuclear power plant safety by earthquakes, terrorism, mechanical breakdown and flooding.

Rubin and Fang discover that the NRC's oversight track record is far from perfect, and that unless urgent action is taken the US could be heading for a nuclear catastrophe of its own.

People & Power airs each week at the following times GMT: Wednesday: 2230; Thursday: 0930; Friday: 0330; Saturday: 1630; Sunday: 2230; Monday: 0930; Tuesday: 0330; Wednesday: 1630. Click here for more People & Power.