An Associated Press investigation has found that Japan exposed thousands of its citizens to risk by failing to use radiation forecasts in the early days of its nuclear crisis.

The government forecasts predicted Karino Elementary School in the town of Namie would be in the path of the plume emerging from the tsunami-hit Fukushima Daiichi nuclear plant.

But the forecasts never reached decision-makers and the school was not cleared out. Instead, it became a temporary evacuation centre.

Parents and others gathered in the playground of the school at the height of the nuclear crisis stemming from the March 11 earthquake and tsunami. Many ate rice balls and cooked in the open air.

It's unclear how much radiation people were exposed to or if they will suffer health problems. But the breakdown may hold lessons for other countries because similar warning systems are used around the world. This was their first test in a major crisis.

Evacuation advisories lifted

Meanwhile on Tuesday, the Japanese government decided to lift evacuation advisories in some areas more than 20 kilometres from the damaged nuclear plant, opening the way for tens of thousands of people to return home.

The advisories warned residents to be prepared to leave in case of worsening conditions at the plant. Although only a warning, many people fled their homes out of fear for their safety or because mandatory evacuation orders in nearby areas deprived them of city services.

Officials said the lifting will allow about 25,000 people covered by the advisories to return home in about a month.

The massive quake and subsequent tsunami destroyed power and cooling functions at the nuclear plant, causing three reactor cores to melt and triggering fires and explosions that spread large amounts of radioactive particles outside the complex.

More than 80,000 residents fled their homes after the disaster.  

Officials at Tokyo Electric Power Co., the utility that operates the plant, and the government have said in recent weeks that the reactors have stabilized and the amount of radiation being released is now minimal.