The journey to Fukushima Daiichi begins at the border of the 12-mile exclusion zone that surrounds the ruined nuclear complex, beyond which life has frozen in time.

Weeds reclaim the gardens of empty homes along a route that emptied on a bitterly cold night almost a year ago. Shop signs hang unrepaired from the huge quake that rattled this area on 11 March, triggering the meltdown of three reactors and a series of explosions that showered the area with contamination. Cars wait outside supermarkets where their owners left them in Tomioka, Okuma and Futaba – once neat, bustling towns. Even birds have deserted this area, if recent research is to be believed.

The reason is signalled by a symphony of beeping noises from dosimeters on our bus. As we drive through a police checkpoint and into the town of Tomioka, about 15km from the plant, the radioactivity climbs steadily, hitting 15 microsieverts per hour at the main gate to the nuclear complex. At the other end of the plant, where the gaping buildings of its three most damaged reactors face the Pacific Ocean, the radiation level is 100 times this high, making it still too dangerous to work there.

Inside the plant's emergency co-ordination building, the air is filled with the sound of humming filters labouring to keep the contamination out. Hundreds of people work here, many sleeping in makeshift beds. Workers in radiation suits and full-face masks wander in and out. A large digital clock showing the current radiation reading inside the building dominates the wall of the central control room, where officials from operator Tokyo Electric Power (Tepco) huddle around computers.

"Our main challenge now is to remove the nuclear fuel from the reactors," explains Takeshi Takahashi in his first interview since he took over as plant manager two months ago. "It's a technically very difficult problem, but we cannot hurry." His predecessor Masao Yoshida was forced to quit in December after being diagnosed with cancer – unrelated to his work, insists Tepco.

Mr Takahashi looks exhausted but says he is satisfied with the progress being made in bringing the plant to "a state of cold shutdown", meaning radiation releases are under control and the temperature of its nuclear fuel is consistently below boiling point.

The term is considered controversial. Engineers have only a rough idea of where exactly the melted fuel lies inside the damaged reactors, or of its exact state. The fuel is being kept cool by thousands of gallons of water that Tepco pumps on to it every day and which it is struggling to decontaminate. Engineers are frantically working to build more water tanks – on a ridge about 65ft from the reactors is a field of 1,000-ton water tanks. A crew is levelling land to make way for more.

We are told to wear our full-face masks for the climax of the visit – a tour of the six reactors. Every inch of our bodies is covered and even in the sub-zero temperatures of Fukushima in February, it is unbearably hot. Thousands of men worked through last year's summer heat of over 30C in this protective gear, struggling to clear debris and bring water to the reactors. "They were dropping like files in the heat," said one worker. "But they just had to keep going."

"The worst time was when the radiation was 250 milisieverts [per year – the maximum, temporary government limit] and we couldn't find people to do the work," explains Kazuhiro Sakamoto, an onsite subcontractor. "We could only work in two-minute bursts, when we were extracting caesium from contaminated water."

Some of that work is clear on site. The concrete building housing Reactor One, blown apart in the first explosion on 12 March, is now completely covered with a tarpaulin to contain its radioactivity. As our bus drives past the building, the beeping dosimeters climb to 100 microsieverts an hour. But as the most badly damaged Reactor Three looms into sight, its mess of tangled metal and steel gives off a startling reading of 1,500 microsieverts. Its cargo of lethal fuel includes plutonium and the roof of the building housing the reactor was blown off in the second explosion. "It's still too dangerous for workers to enter Reactor Three," says engineer Yasuki Hibi.

The state of Reactor Two, meanwhile, sparked some panic last week after Tepco reported that the heat of the fuel inside was climbing and apparently resisting efforts to bring it down. The nightmare scenario of another out-of-control reactor was briefly conjured up by the media before Tepco banished it by claiming faulty equipment. "We've identified the problem as a broken thermometer," says Mr Takahashi, adding: "I'm terribly sorry to everyone for causing so much concern."

Tepco officials constantly apologise. The apologies have become perfunctory and ritualised, failing to douse public anger over the scale of the disaster, or some of the company's sharp-elbowed tactics since it began. Compensation has dribbled into the pockets of over 100,000 evacuees who have lost everything and are stuck in legal limbo, without homes or clear futures. In one now infamous incident, the utility argued against a compensation claim by a golf course operator, saying radioactive materials from the nuclear plant belong to individual landowners, and are not the company's responsibility. Lawyers for the Sunfield Nihonmatsu Golf Club, 28 miles west of the plant, said they were "flabbergasted" by the argument.

But here at the Daiichi complex at least, the apologies seem genuine. Work here is hard, unrelenting and, in the long term, possibly fatal. The depth of feeling about this catastrophe is etched on the faces of hollow-eyed managers like Mr Takahashi, who live day and night in one of the world's least hospitable workplaces. He says he is motivated above all by one thing: "We will try to allow people to return to their homes as early as possible."

It is a mammoth task. Japan's government has admitted that dismantling the reactors and its 260-ton payload of nuclear fuel will take up to 40 years. Many people believe the government and Tepco will eventually be forced to recognise that the people who fled from this plant a year ago may not return for decades. In the meantime, the work at Fukushima Daiichi goes on. And on.

Fukushima timeline

11 March 2011

At 2.46pm a magnitude 8.9 earthquake strikes Japan's north-eastern coast, triggering a devastating tsunami and a series of strong aftershocks.

12 March

A state of emergency is declared. About 170,000 people are evacuated from a 20km (12-mile) zone around the Fukushima nuclear plant after an explosion in one of its reactors.

13 March

Around 190 people are treated in hospital for radiation exposure.

17 March

Helicopters dump tons of water over the Fukushima plant in an attempt to cool the overheating nuclear reactors as fears over a meltdown grow.

22 March

Abnormal radiation levels are detected in tap water, vegetables, milk and fish.

25 March

Japan expands the exclusion zone around the plant, and asks a further 130,000 residents to evacuate as fears over the extent of the damage to the reactors worsen.

26 March

Levels of radioactive iodine in the sea near the Fukushima nuclear plant are found to be 1,250 times higher than the safety limit, according to officials.

30 June

Radiation contamination is found in 10 children's urine samples, according to a citizen's group.

19 July

Transport of beef from Fukushima is prohibited, but a crisis ensues after it emerges that meat from cattle fed on contaminated hay has already been distributed nationally.

8 September

A total of 15,000 terabecquerels of radiation were released into the sea from the damaged plant, according to the Japan Atomic Energy Agency.

29 September

Core temperatures for all three damaged reactors dip below 100C for the first time.

28 October

The Fukushima plant released twice as much radioactivity into the atmosphere as originally thought, a study by the Norwegian Institute for Air Research finds.

27 January 2012

The Japanese government had a secret plan to evacuate everyone living within 155 miles of the plant should the situation have spiralled out of control, it emerges. This would have included the Tokyo metropolitan area – home to 30 million people.

3 February

Researchers working around the Fukushima plant say bird populations there are dwindling, one of the first indications of the impact of radioactive fallout on local wildlife.

Heavy tolls

100,000 people were displaced by the Fukushima disaster unsure when, or if, they can return home

3,000 people work at the plant each day, according to Tepco

80% of Japanese people are anti-nuclear, according to a poll in June 2011

Belfast Telegraph