They only eat two meals a day - emergency crackers and vegetable juice for breakfast, and a packet of rice with chicken, fish or curry for dinner.
In the evenings, they gather around in a safe room to cheer "Let's do our best!" and clap once, before wrapping themselves with blankets and going to sleep on the floor.
Kazuma Yokota, a nuclear safety agency inspector based at the plant, told Japanese national broadcaster NHK about the five days he spent at Daiichi observing the workers.
"Workers sleep in conference rooms, hallways or near bathrooms. Each person is given one blanket, everyone sleeps on the floor in rows," Mr Yokota said.
"We want to avoid staying too long as much as we can, because we are exposed to radiation every day."
The employees of Tokyo Electric Power Company (TEPCO), dubbed the Fukushima Fifty by foreign media for working in shifts of 50, have been battling to save Japan from a nuclear crisis since a devastating earthquake and tsunami damaged the Fukushima Daiichi power plant on March 11.
Now, one of them has spoken out about the difficult working conditions he and his colleagues face - including the reality of being contaminated by the high radiation levels around the nuclear facility.
His comments came as news broke that Japanese officials had recorded radioactive iodine levels of 3355 times above the legal limit, Jiji press reported, and as Japanese Prime Minister Naoto Kan said yesterday that his country was on "maximum alert" over the nuclear situation at the plant, about 240 kilometres north of Tokyo.
Mr Yokota, 39, who was described as looking exhausted by Agence France-Presse (AFP), said he was exposed to 883 microsieverts - a radiation dose similar to almost nine chest X-rays - during the five days.
Every morning, the TEPCO workers, which number between 270 to 580 at any given time, hold a meeting to discuss the reactors' conditions and tasks for the day, The Yomiuri Shimbun newspaper quoted Mr Yokota as saying.
Most of them work from 10am to 5pm, while others on night shifts monitor the plant's machinery readings, he said.
Their food and water intake is rationed.
"For breakfast we eat emergency high-energy biscuits. Dinner is quick-boiled rice and canned food," Mr Yokota said, adding: "I don't think the workers are getting enough nutrition from the food they are receiving."
The workers are restricted to packaged food because of radiation contamination fears, Reuters reported. They stuff the food into their mouths once they open the packets to avoid contact with radiation.
The high levels of radiation contamination in the air at the plant also means the workers wear masks even in the safe room where they eat and sleep.
The Yomiuri Shimbun said each TEPCO worker is only allowed 1.5 litres of water per day, so they do not bathe, and wash their hands with alcohol instead of water.
They rarely change their clothes, and some workers have complained about not being able to change their underwear, Mr Yokota said.
When they are working, they wear protective suits, double-thickness gloves and masks. They carry flashlights so they can operate in the darkened areas of the plant, where they lay electric cables, clear rubble, hose down overheating reactors and check equipment, AFP reported.
At night, the workers sleep "packed together like sardines" in cold conditions on top of lead sheets laid on the floor to reduce radiation in the building, the Yomiuri Shimbun said.
Conditions at the start of the crisis were harsher, one worker told the Yomiuri Shimbun.
"Right after the accident, we were getting by on just dried bread," the worker at the plant, who was not named, told the newspaper.
The workers worked 23-hour shifts for the first few days and slept for only one hour before going back to work.
"Since we were working with hardly any sleep, we got so exhausted we could hardly chew the stuff," the worker said. "Everyone was just dreaming of a good cup of tea."
A string of emails between the workers and a TEPCO employee in Tokyo published by The Wall Street Journal on Monday and verified by a TEPCO spokesman also detailed the emotional difficulties the crew were facing.
"I just wanted people to understand that there are many people fighting under harsh circumstances in the nuclear plants. That is all I want," the unnamed worker wrote.
"Crying is useless. If we're in hell now all we can do is to crawl up towards heaven. Please watch out for the hidden strength of nuclear power. I'll make sure we will make a recovery."
The worker added in another email: "As you know, most of the workers ... are local residents and victims of the quake. There are many workers whose houses were washed away.
"My parents were washed away by the tsunami and I still don't know where they are. ... I'm engaged in extremely tough work under this kind of mental condition ... I can't take this any more!
"All of us, including myself, are victims of the disaster. But we are all working hard to complete our tasks as [TEPCO] employees, before thinking of ourselves as disaster victims."
A Japanese professor of disaster psychology said the workers' physical and emotional stress needed to be tackled if TEPCO did not want mistakes to occur.
"This is similar to a war zone and things need to be addressed, including providing proper back-up for the workers who are under immense stress," Professor Hirotada Hirose of Tokyo Woman's Christian University told Reuters.
"If this continues, productivity and morale will fall and workers will become likely to make mistakes. We cannot afford that."
Government spokesman Yukio Edano said the focus was on avoiding a nuclear disaster.
"We have been doing the best we can for the workers but it hasn't necessarily been enough because we've had to put our priority on containing the accident."
But the Industry Minister, Banri Kaieda, said TEPCO was expected to improve the working conditions, Kyodo news agency reported.
"The workers, as well as the Self-Defence Forces and firefighters, are working under extremely harsh conditions ... so [the conditions for] food and sleep must be improved first," Mr Kaieda was quoted by Kyodo as saying.
The International Atomic Energy Agency, the UN's nuclear watchdog, said the situation at the power plant remained "very serious".
More than a dozen TEPCO workers have been injured since March 11. Two were taken to hospital with suspected radiation burns after stepping into contaminated water last week.