Posted on behalf of David Cyranoski.

With the Fukushima nuclear reactors seemingly under control, the Japanese government is now facing the daunting task of cleaning up the highly contaminated areas around the reactors so that residents can move back. But it is estimated that more than 100 million cubic metres of soil and debris will need to be removed. Where does one begin?

On Monday, the Japan Atomic Energy Agency (JAEA) selected three major decontamination demonstration projects. On Wednesday it followed with the announcement of another 25 grants for smaller, technology-based projects.

The goal for each of the three demonstration projects is to show the capability of reducing radiation levels to less than 20 millisieverts a year ― the legal threshold at which people must be evacuated ― “with an economically feasible, efficient, and effective decontamination method that limits the amount of radioactive waste as much as possible while ensuring the safety of workers”, according to the JAEA.

Each group will receive roughly ¥600 million (US$7.7 million) for each of the four cities or towns for which it will take responsibility. Taisei Corporation, for example, will be covering Minamisoma, Kawamata, Namie, and Iitate. The 12 towns are all either in the original 20-kilometre exclusion zone or in the extended exclusion zone covering the plume to the northwest where high levels of radioactive material fell (see Does Japan’s new Fukushima exclusion zone add up?).

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Scientists have downplayed the significance of the detection of radioactive xenon at the Fukushima nuclear power plant in Japan, announced today.

As xenon radionuclides have short half-lives of up to just a few days, the detection, if confirmed, would mean that nuclear fission reactions of some form had restarted. But experts say that small amounts of fission in the reactor core would not be that surprising, and there seems no danger of either a self-sustaining critical chain reaction or significant release of fission products into the environment. Nature has also learned that ultrasensitive radionuclide detectors in the region, part of a global system to detect minute radionuclide signatures from atomic bomb tests, have so far not detected a trace of any newly-released xenon.

Tepco, the company that operates the Fukushima power plant, announced earlier today that nuclide analyses of exhaust gas from the reactor containment vessel of reactor 2 yesterday found a possible detection of xenon-133 (half life of just over 5 days) and xenon-135 (half-life of 9.14 hours). It noted, however, that there was no change in the temperature or pressure of the reactor, and no increase in radiation levels around the plant. Nonetheless, as a precaution it today injected into the reactor a solution of boric acid which strongly absorbs neutrons and so dampens fission reactions.

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Japan has launched a long-term project to monitor children near the Fukushima nuclear plant for thyroid problems.

Yesterday health workers tested the first 100 of a planned 360,000 children who were under 18 when the crisis began in March. They will be tested again every two years until they turn 20, then every five years thereafter.

Children and pregnant women are particularly vulnerable to thyroid damage from radioactive iodine – the New York Times reports that at least 4,000 cases of thyroid cancer in children have been linked to the 1986 Chernobyl meltdown. Previous screening of children around Fukushima showed minimal doses of radioactive iodine (see ‘Fukushima health risks scrutinized’).

Read all of Nature’s coverage of the Fukushima disaster here. For coverage in Japanese, go here.

Monju, Japan’s prototype fast breeder reactor, has had its research budget slashed. This might not come as a big surprise, given the anti-nuke sentiment in Japan and the tattered state of its nuclear energy policy. Still, with this latest blow, the woeful state of the ill-fated reactor is all the more striking. It could be maintained — with the help of a one-off Y20 billion yen (US$262 million) allocation — but the annual research budget will be cut 70%~80% from its previous Y10 billion.

Monju reached criticality in 1994 but was shut down the following year because of a fire triggered by a sodium coolant leak. It took the government over 14 years to demonstrate safety, overcome scandals related to tampered video images, and garner local support for restarting operations. But then, three months after it did so in May 2010, something happened that is still difficult to fathom. In August, 3.3-tonne device fell into the reactor’s inner vessel, cutting off access to the plutonium and uranium fuel rods. After a couple failed attempts, they finally dislodged the device in June 2011.

Monju was to be the cornerstone of Japan’s plans to use MOX (mixed oxide) fuel, but those plans seem to have disintegrated. Monju already faced fiery opposition.

One might start to wonder how much longer it can limp along.

The meltdown of three nuclear reactors at the Fukushima power plant has led to an ongoing crisis in Japan. Nature Video provides an update on efforts to stabilize the reactors, and the consequences of the emergency for Japan and nuclear power worldwide.

Check out our previous video on the emergency itself.

See also our news special on the Fukushima crisis, and our coverage in Japanese.

This Sunday (11 September) marks the six-month anniversary of the triple meltdown at the Fukushima Daiichi nuclear power plant in Japan. The accident has slipped from the headlines, but new data are coming out all the time. Some of the most recent findings are allowing the best comparison yet of Fukushima with Chernobyl.

A lot of media outlets (ourselves included) first made the Fukushima-Chernobyl comparison back in April, when the Japanese revised their estimate of the Fukushima accident—rating it a seven on the seven-point international INES scale. The conclusion most reached at the time was that, although the rating was the same, Fukushima was a much smaller accident.

A couple of things have changed since those first reports. First, the Japanese doubled their estimate of the radiation released by Fukushima in June to 7.7×10¹⁷ Becquerels (Bq). Then, on 30 August, they released the first maps of radioactive caesium-137 (Cs-137) contamination from the plant. Cs-137 has a half-life of 30 years, and it’s considered the major long-term contaminate for both accidents.

With the new Cs-137 data, we can now directly compare the fallout from Chernobyl to Fukushima. Check out the Google Earth mashup above (zoom out to see Chernobyl on top of Fukushima, and rotate over to the Ukraine to see Chernobyl in context).

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