Following a major earthquake in Japan, a 15-metre tsunami disabled the power supply and cooling of three Fukushima Daiichi reactors, causing a life-threatening nuclear accident on 11 March, 2011. All three cores largely melted in the first three days and things looked extremely dire – but amazingly the reactors were held in check and the millions of lives affected were saved.

But how? Well tonight’s documentary FUKUSHIMA: A NUCLEAR STORY sheds more than a little light on the subject, by taking us on an exclusive journey inside the triple tragedy that hit Japan that fateful day. The fact-filled but still compelling film is jam-packed with insight into what really happened at Fukushima after the quake and the tsunami that followed.

Following a major earthquake in Japan, a 15-metre tsunami disabled the power supply and cooling of three Fukushima Daiichi reactors, causing a life-threatening nuclear accident on 11 March, 2011. All three cores largely melted in the first three days and things looked extremely dire – but amazingly the reactors were held in check and the millions of lives affected were saved.

But how? Well tonight’s documentary FUKUSHIMA: A NUCLEAR STORY sheds more than a little light on the subject, by taking us on an exclusive journey inside the triple tragedy that hit Japan that fateful day. The fact-filled but still compelling film is jam-packed with insight into what really happened at Fukushima after the quake and the tsunami that followed.

It goes without saying that the Great East Japan Earthquake of magnitude 9.0 at 2.46 pm on Friday 11 March 2011 did considerable damage in the region, and the large tsunami it created caused very much more. The earthquake was centred 130 km offshore the city of Sendai in Miyagi prefecture on the eastern cost of Honshu Island (the main part of Japan), and was a rare and complex double quake giving a severe duration of about 3 minutes. An area of the seafloor extending 650 km north-south moved typically 10-20 metres horizontally. Then Japan moved a few metres east and the local coastline subsided half a metre. The tsunami inundated about 560 sq km and resulted in a human death toll of over 19,000 and huge damage to coastal ports and towns with over a million buildings destroyed or partly collapsed.

Eleven reactors at four nuclear power plants in the region were operating at the time and all shut down automatically when the quake hit. Subsequent inspection showed no significant damage to any from the earthquake – they proved robust seismically, but were then vulnerable to the tsunami. Power was available to run the Residual Heat Removal system cooling pumps at eight of the eleven units, and despite some problems they achieved 'cold shutdown' within about four days. The other three, at Fukushima Daiichi, lost power almost an hour after the quake, when the entire site was flooded by the 15-metre tsunami. This disabled 12 of 13 back-up generators on site and also the heat exchangers for dumping reactor waste heat and decay heat to the sea. The three units lost the ability to maintain proper reactor cooling and water circulation functions. Electrical switchgear was also disabled. Thereafter, many weeks of focused work centred on restoring heat removal from the reactors was undertaken by hundreds of employees as well as some contractors, supported by firefighting and military personnel. Some of the Tepco staff had lost homes, and even families, in the tsunami, and were initially living in temporary accommodation under great difficulties and with some personal risk.

Four reactors were written off due to damage in the accident, but after weeks, the three aforementioned reactors were stable and by July they were being cooled with recycled water from the new treatment plant. Official 'cold shutdown condition' was announced in mid-December. Amazingly, there have been no deaths or cases of radiation sickness from the nuclear accident, but over 100,000 people were evacuated from their homes to ensure this. Government nervousness – or perhaps caution, in my humble opinion - delays the return of many.

So, to the powerful documentary - shot from March 11th, 2011 through March 2015 - that sheds some light on what really happened at Fukushima. What is it that saved Tokyo from a nuclear disaster? We find out when pool of foreign journalists are allowed to enter the Fukushima-Daiichi power plant, many who have waited two years to uncover the truth about the 2011 accident hidden behind those walls.

The main subject is Italian news reporter Pio d’Emilia, who has lived in Japan for over thirty years. He was in Tokyo the day of the earthquake and he travelled through many of the towns and villages hit by the tsunami and reportedly illegally entered the “exclusion zone”. At the gate of the nuclear plant he was refused entry and it wasn’t until June 2013 that the plant operator would allow him in. A man obsessed, he collected over 300 hours of footage consisting of shocking images and interviews with local people, authorities and officers, focusing on what he calls the social “collateral effects” of past and present decisions by the government and the nuclear community. This, along with an exclusive interview with former Prime Minister Naoto Kan reveals how Tokyo and all of Japan was saved from a much greater catastrophe purely by chance.

At times heart-stopping and baffling in turn, this is an important documentary for those of us living in the age of a) unexpected natural disasters a-plenty and b) nuclear power as a viable option for many countries around the world. A great watch.