IWAKI, Japan - To some of the men who earn as little as $100 a day to work inside Japan's Fukushima Daiichi, the plant at the center of a year-old nuclear disaster is far from safe - despite the official line.

Operator Tokyo Electric Power and the Japanese government say the tsunami-crippled reactors are all in a "state of cold shutdown" and are keen to give the impression that there is just cleaning up to do.

They acknowledge it is the work of a few decades - perhaps 40 years - but nonetheless insist things are under control.

But that is not how those who spend their days inside the plant see it.

"I can clearly say it's not safe at all," said one worker in his 50s, a subcontractor who has been working on the plant's cooling system since September.

The man did not want to be identified for fear of losing the $100 daily paycheck he receives.

"There are many spots where radiation levels are extremely high," he said.

The man said subcontractors like him were treated like animals.

In the height of summer with the mercury rising to 38 C, workers had to go for up to three hours at a time without water because they were unable to take off their masks.

There have been deaths on site - a 60-year-old subcontractor's fatal heart attack in May was put down to overwork, according to a labor standards inspector - although TEPCO says none was related to radiation exposure.

Chie Hosoda, a spokeswoman for the utility, admits conditions at the plant were unacceptable in the past, with the radiation exposure of some workers left unmeasured because of a shortage of dosimeters.

"But working conditions have improved now, and we are strictly checking the radiation exposure of all workers," Hosoda said. 

Three of the four reactors at Fukushima Daiichi went into meltdown after the tsunami swamped their cooling systems in March 2011.

Fuel began to overheat and the day after the waves struck, an explosion - the first of several - ripped through a reactor building.

Emergency workers tried to cool the rapidly heating rods with any water available, including from the sea.

A month on, Tokyo finally upgraded its assessment of the severity of the nuclear emergency to a maximum seven on an international scale - equal with Chernobyl.

It was not until May 5 that workers were able to get inside the reactor building for the first time, to see the enormity of the task ahead of them.

Engineers, nuclear experts and ordinary electricians are among the 3,600 people working at the plant every day, and TEPCO says it has no problems securing a work force despite the obvious hazards.

But Katsuyasu Iida, secretary-general of Tokyo Occupational Safety and Health Centre, a support group for low-paid workers, warned the utility may face a labor shortage "if it fails to improve working conditions".

Many with experience in the industry shy away from the plant.

"Those who used to work at the Fukushima nuclear plant for a long time do not go to Daiichi because it's dangerous," one worker told the Tokyo Shimbun newspaper.

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