“I was in a school gymnasium in Ishinomaki that had been turned into a makeshift morgue and there was a steady stream of military trucks pulling up and unloading bodies,” says Gilhooly, who was on assignment for several British and US media outlets.

“I cannot erase the memory of a muddy shoe falling off the foot of an elderly man wrapped in a flowery blanket and gently being replaced by one of the officials given the task of tallying the arrivals.

“That was somebody’s father, grandfather, brother – and it could also have been any one of us, I suppose,” he says. “But it wasn’t just that. It was the pathos of the gesture, returning a slip-on shoe to a dead man’s foot.”

Largely unbeknown to survivors of the earthquake, as well as the military and civilian rescue teams scrabbling frantically to locate others buried in the rubble of their homes, the situation at the Fukushima Daiichi nuclear power plant, just 100km to the south, was deteriorating rapidly on March 13.

The first hydrogen explosion had des­troyed the build­ing that housed the No 1 reactor the day before and, despite assur­ances from Tokyo Electric Power Co (Tepco) and the govern­ment that there was no danger to the public, fears were mount­ing that the crisis was on the verge of becoming a catastrophe.

Similar explosions rocked the second and third units over the next couple of days, radiation levels spiked, large-scale evacuations were ordered and it became increasingly difficult for the authorities to insist that the situation was under control.

Patently, Gilhooly says, it wasn’t. And that was the genesis of the book Yoshida’s Dilemma: One Man’s Struggle to Avert Nuclear Catastrophe: Fukushima - March 2011 , which will be released today (March 11), the sixth anni­versary of the tragedy.

The book is named for Masao Yoshida, the manager of the power plant, who opted to remain at his post after the reactors had been hit by a 13-metre tsunami. Yoshida – among those dubbed by the media the “Fukushima 50” – oversaw efforts to keep the reactors cool, braving near-constant aftershocks and hydrogen explosions. He is best remembered, however, for defying direct orders from Tepco officials in Tokyo to stop pumping seawater into one of the damaged reactors in a last-ditch attempt to cool them. The company was worried that the equipment would be damaged by exposure to seawater.

By the time Gilhooly tracked Yoshida down, he had taken early retirement and was undergoing treatment for oesopha­geal cancer. A heavy smoker, Yoshida would speak to Gilhooly only off the record. But that was more than enough to gain an under­standing of the actions of the man, who died in July 2013.

“I think anyone who met him would say he came across as very forthright, sincere and affable and not someone who saw himself as a hero,” Gilhooly says. “He expressed regret about the distress caused to families of workers, but he never questioned his decision to spray seawater onto the reactors.

“For all the things that could or could not have been done differently, one thing I am sure he was happy to have played a central role in is the on-site emergency response bunker, which was built just months before the disasters.

“The planning of that structure was overseen by Yoshida while he was stationed at Tepco headquarters – and was itself the outcome of an accident at another Tepco nuclear plant, in Niigata,” Gilhooly says. “If that response centre, which had its own dedicated generator, powering communications and air conditioning, not to mention medical and other supplies, hadn’t been there, there is little doubt that the outcome would have been significantly more catastrophic.

“Without it, there would have been nowhere to shelter and, with radiation above levels that a human can survive, workers would have had no choice but to pull out.”

The scenario of an unchecked nuclear disaster hardly bears thinking about.

In the years since the earthquake, Gilhooly has spent many months in the Tohoku region of northeast Japan, his path smoothed by the fact he spent three years in Fukushima prefecture as a teacher immediately after arriving in Japan and has a good understanding of the ben, or local dialect.

As well as speaking with Yoshida, workers and officials of Tepco – who alternated between being helpful and somewhat less so – he interviewed Naoto Kan, Japan’s prime minister at the time of the disaster, and dozens of people who were evacuated as the radioactive plume passed over their communities, many of whom are still unable to return.

“More than anything I wanted to hear the human stories and to try and find out what actually happened. I also hoped it might elicit some insights into a pretty basic question: is a country like Japan – with 10 per cent of the globe’s major earthquakes – really suited to having so many nuclear reactors? Or any reactors, for that matter?”

While Gilhooly is careful not to take sides in the pro- and anti-nuclear power debate, the almost inescapable conclusion is that nuclear power is a highly dangerous technology – maybe even too dangerous to be employed using the current Japanese business model, where the “nuclear village” shuts out criticism, and even knowledge, of its often dangerous operational practices and decisions.

“It’s difficult to think that nuclear power on the global level is going to simply disappear, not with­out a viable ‘base-load’ energy alternative,” he says. “However, it’s no surprise to hear the view that an island nation that experiences one-tenth of the world’s largest quakes and is suscep­tible to mega-tsunami should probably be looking at other forms of energy.

“Another opinion I heard was that considering what Japan has gone through, in Hiroshima and Nagasaki and now in Fukushima, the nation should really be looking at becoming a world leader in new energies – but, for one reason or another, it seems to be dragging its feet.”

For many who survived, ignorance continues to com­pound the pain.

“I felt particularly sad when I heard a story from a couple who had survived the disasters – although they lost their home – and taken a holiday to Kyushu,” Gilhooly says. “Along the way, people asked them questions and their answers and dialect betrayed their identity. From then they were treated like lepers.

“It’s another reason I wanted to write this book; these types of issues are not going to go away any time soon.”