Fukushima update: radiation levels remain high

by Jess Miller

March 17, 2011

Latest updates

After days of news reporting one explosion after another at the Fukushima nuclear plant, there is finally a break in reports of new explosions.

Radiation levels remain high around the plant.

All efforts are being focused on restoring water levels at the sites spent nuclear fuel storage pools. There is an emerging experts consensus that there is only a day or two to raise water levels in spent nuclear fuel pools to avert a much larger catastrophe.

Cooling efforts

Two large Chinook helicopters were used to drop water on the spent fuel pools in reactors 3 and 4 at about 10am. Originally, 40-50 drops of 7.5 tons each were reported to be planned, but only four have been conducted so far: three drops on reactor 3 and one on reactor 4, after which the helicopters pulled back to limit crews’ radiation exposure. Out of the total amount of 30 tons, 8 tons were believed to have made it to the pools.

More drops are being considered. The police have brought in 11 special vehicles equipped with water cannons and 4-ton water tanks. These are being used to spray water into the spent fuel pools. Operation has been reported for hours to be starting shortly. Damage to the road and debris have prevented access by heavy vehicles until this morning.

A new power line is being installed to provide grid power to pumps and other equipment; it is expected to be completed some time this afternoon.

The spent fuel pools have an area of roughly 150-200m2, so raising the water level by one meter requires about 200 tons of water.

At best, the spraying seems to be buying some time until more efficient cooling methods can be put in place. In testimony to the truly heroic efforts of plant operators, IAEA has published information from Tepco on the injuries sustained by rescue workers (updated at 17 March 01:15 UTC.)

Radiation levels

Levels above reactors reported as 4.13 “mSv” at 1000 feet and 87.7 “mSv” at 300 feet. The statements by the government and the Tepco spokespeople seem to contradict the reported values. The helicopters are equipped with lead panels and crews wearing protective gear, but were unable to hover above the reactors to improve accuracy and had to pull back after only 15 minutes, yet the government-authorised emergency dose limit of 250 mSv/h would allow the crews to stay at 1000 feet for 48 hours, even without shielding.

Ibaraki’s (130 km south of Dalichi) radiation readings on Tuesday just before the monitors went “under survey” are posted online. The readings measure at 3.4 micro-Sv/h = 30 milli-Sv per year. Current value is 0.92 micro-Sv/h = 8 mSv/y. In Saitama and Tochigi, close to Tokyo, readings of 1.2 and 1.3 microSv/h were measured yesterday.

Heightened fears and new evacuations

The US and French nuclear agencies warned yesterday of the possibility of a major catastrophe. The Japanese government has evacuated at least an additional 10,000 people from the 20-30km zone around the nuclear plant.

There are still tens of thousands of people within the zone, as the 71,000 strong city of Minamisoma falls within the zone. The evacuated people will be given radiation scans. The US Embassy in Japan issued a warning last night to US citizens within 80-kilometer to evacuate as a precautionary measure. The US has chartered aircraft to help Americans leave Japan and had authorised the voluntary departure of family members of diplomatic staff in Tokyo, Nagoya and Yokohama — about 600 people.

China moved to evacuate its citizens from northeastern Japan earlier in the week. For more on the next steps check out this expert interview.

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