At the same time, the enormity of cleaning up the disaster was revealed in Japanese government report released today, which said that an irradiated tract of land the size of Tokyo will have to be disposed of.

Removing topsoil containing caesium and other radioactive contaminants is likely to leave a pile of nuclear waste almost 29 million cubic metres high – enough to fill one of the city’s largest stadiums 80 times, the report indicated as quoted by The Irish Times.

After the devastating earthquake and tsunami on March 11^th knocked out cooling systems and caused meltdowns of nuclear fuel rods at three of the plant’s six reactors, TECPO’s main battle has been trying to cool them and bring temperatures below the boiling point.

Cooling while battling radiation releases

Temperatures at two of the three reactors had already dropped below 100 degrees Celsius in July and early September, leaving just one reactor above boiling point.

But temperatures at the last of the three reactors fell to 99.4 degrees on Wednesday, TEPCO spokesman Takeo Iwamoto told Reuters.

“The temperature has been moving up and down but it is on a steady decline,” Iwamoto said. “We have cleared the temperature issue and taken a step forward towards achieving cold shutdown by the end of this year.”

Technically, a cold shutdown occurs when water used to cool nuclear fuel rods remains steadily below 100 degrees, preventing the fuel from reheating.

But TEPCO has said it won’t declare a cold shutdown until other criteria are met, like further reducing the amount of radiation being emitted from the plant. Cold shutdown is a criterium for the Japanese government to allow resettlement of evacuees from the region of the plant.

Bellona executive director and nuclear physicist Nils Bøhmer saw the temperature drops as a good sign, but repudiated plans of resettling the evacuaton zone around the plant. 

“The cold shutdown, that is maintaining core temparatures below 100 C is a good sign since that means the beginning of the end of the Fukushima accident,” said Bøhmer. “But the risk of future releases will still be present, and because of all the nuclear fallout in the Fukushima restricted zone, it will take years, if not decades before that zone will be inhabited again.”

Last week the Japanese government and TEPCO said at a monthly review of the Daiichi plant’s cleanup timetable that they are now aiming to bring the plants to a cold shutdown within this year, instead of by January as initially planned, with their cleanup work proceeding steadily.

Clean up complications

Decontamination work from the world’s worst nuclear accident in 25 years could extend to a 2,400sq km zone across the four worst affected Japanese prefectures, according to the environment ministry report, the first official assessment.

Experts have advised the government that about 5cm of topsoil would have to be excavated to make the land safe. The laborious decontamination process will also involve removing leaves and dirt from woodland, which covers 60-70 percent of the affected area.

More than 80,000 people have been evacuated from a 20 kilometre radius around the crippled nuclear plant and the most heavily irradiated towns and villages nearby. But radioactivity in cities up to 60 kilometres from the plant has exerted serious strain on local life.

Radioactive hotspots in some highly populated areas exceed those found in Chernobyl, scene of the 1986 nuclear disaster. The environment ministry is focusing its decontamination on areas where radiation exposure is more than 5 millisieverts a year, roughly double UN estimates for safe background radiation.

Minister for the environment Goshi Hosono faces fierce resistance from local officials in Fukushima to a tentative plan to temporarily store the radioactive waste in the prefecture while the government looks for a permanent home for it, The Irish Times reported.

A budget of $2.9 billion has already been allocated for the clean-up, but the environment ministry has asked for another $5.8 billion for this fiscal year alone, according to Kyodo News.