Japan must dispose of 29 million cubic metres of contaminated soil after the Fukushima nuclear crisis.
Six months after the March earthquake and tsunami triggered reactor meltdowns, explosions and radiation leaks at Fukushima Daiichi nuclear power plant on Japan's northeast coast, the size of the task of cleaning up is only now becoming clear.
In the first official estimate of the scope and size of the cleanup, the ministry said that contaminated zones where radiation levels need to be brought down could top 2,400 square km, sprawling over Fukushima and four nearby prefectures.
Tokyo Metropolitan prefecture has a total area of 2,170 square kilometers.
The government has so far raised 220 billion yen ($2.9 billion) to be used for decontamination work, but some experts say the cleanup bill cost reach trillions of yen and the environment ministry has requested an additional 450 billion yen in a third extra budget.
If a 5 cm layer of surface soil, likely to contain cesium, is scraped off affected areas, grass and fallen leaves are removed from forests, and dirt and leaves are removed from gutters, it would amount to nearly 29 million cubic metres of radioactive waste, the ministry report said.
The government needs to decide where to temporarily store such waste and how to dispose of it permanently.
Japan has banned people from entering within a 20 km radius of the plant, located about 240 km northeast of Tokyo and owned by Tokyo Electric Power Co. Some 80,000 people were forced to evacuate.
The government aims to halve radiation over two years in places contaminated by the crisis, relying on both the natural drop in radiation as time passes and by human efforts.
The ministry's estimate assumes that cleanup efforts should be mainly in areas where people could be exposed to radiation of 5 millisieverts (mSv) or more annually, excluding exposure from natural sources.
The unit sievert quantifies the amount of radiation absorbed by human tissues and a mSv is one-thousandth of a sievert.
Radiation exposure from natural sources in a year is about 2.4 mSv on average, the U.N. atomic watchdog said.