Ground Self-Defense Force choppers dumped water bags, a Tokyo police water cannon unsuccessfully tried to spray water and five enclosed GSDF firetrucks later took on the desperate attempt to cool spent nuclear fuel rods in a storage pool suspected of drying up at the Fukushima No. 1 atomic plant’s No. 3 reactor.

Of the effort by two GSDF Chinook choppers to drop 30 tons of water on the pool, Chief Cabinet Secretary Yukio Edano said, “We are still investigating” whether the drop helped fill the pool.

Then shortly after 7 p.m., a Tokyo police truck equipped with an antiriot high-pressure water cannon sprayed the pool but high radiation levels soon forced the truck to retreat. The five GSDF firetrucks then took over the operation until after 8 p.m. as fears mount of a greater radiation leak. It was not immediately clear if the operation succeeded.

If the storing pools, which are located outside the containment vessels, dry up, the spent nuclear fuel will melt down, releasing large amounts of radiation.

The pools at reactors 3 and 4 malfunctioned after Friday’s killer earthquake and tsunami, which also shut down the plant’s three reactors in operation at the time. Plant operator Tokyo Electric Power Co. has been unable to monitor the water levels and temperature, or get water into the pools.

The government gave the green light to the water drop despite the risk of fire or scattering radiation, and the dangers to the helicopter crews.

Defense Minister Toshimi Kitazawa said he gave the go-ahead as the radiation level was 4.13 millisieverts per hour at an altitude of 300 meters and 87.7 millisieverts at 100 meters.

The drop was made from less than 100 meters, SDF chief Ryoichi Oriki said.

At around 10 a.m., the CH-47s dropped 7.5 tons of water in four runs above the No. 3 reactor building after a separate chopper first calculated the radiation levels in the area. The choppers were only allowed to fly up to 40 minutes to limit the crews’ exposure to radiation.

A GSDF helicopter crew flying over the complex Wednesday night confirmed the No. 4 reactor’s spent rod pool contained enough water to cover the fuel, Tepco claimed.

Based on this information, the government and the utility decided to drop water first on the No. 3 reactor building, where the water level was lower, Tepco said.

The radiation level remained unchanged after the water drop, Tepco said.

The government aborted a Wednesday water drop because the radiation level was too high.

Tepco was still trying to install a temporary electric power source in a bid to restore the pumps that send water to the reactor cores and pools. One official said earlier the plan had a “high probability” of success.

In Washington, Gregory Jaczko, chief of the U.S. Nuclear Regulatory Commission, reportedly told a House Energy and Commerce subcommittee hearing that the pool at the No. 4 reactor was empty.

Based on the NRC’s finding, the U.S. Embassy asked American citizens living within an 80-km radius of the Fukushima No. 1 power station to evacuate as a precautionary step.

But Japanese officials challenged Jaczko’s assessment, saying he was misinformed.

“There was a slight delay conveying to the U.S. side the information about whether or not there is water” in the pool holding spent nuclear fuel rods at the No. 4 reactor, Edano told a news conference.

Electricity for the No. 1 and 2 reactors had been expected to be restored later Thursday. If and when that happens, this would allow the cooling system to start pumping water again.

But Edano wasn’t optimistic.

“It is likely to have some effect, but not all the problems will be resolved,” he said.

At present, fire engines are pumping seawater into the Nos. 1, 2 and 3 reactors, whose pumping systems have failed.

Information from Kyodo added

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