Japan: Emergency water drop operations begin at Fukushima; new photos show damage at stricken nuclear plant

(screengrab of NHK TV coverage of the third helicopter water drop in the current operation, around 10am local time in Japan.)

Two helicopters, modified to help protect pilots from radiation, have just begun missions to drop tons of sea water on the quake and tsunami-stricken Fukushima 1 plant in Japan. The live TV coverage of the water drops has been chilling to watch, knowing what is at stake both for the pilots and the population they hope to protect.

Separately, according to reports in the US and from news agencies in Japan, the US military will also soon fly unmanned aerial drones over the plant to take photos of the inside of the building that houses the No. 4 reactor.

"The water is depleting rapidly at the number 3 and number 4 units, and the government is placing urgent priority on providing water now," says a senior commentator on NHK right now, as I type.

An explosion occurred at reactor No. 4 on Tuesday, and was believed to have been a hydrogen explosion. White smoke has been rising from this site on Wednesday, and the spent fuel is believed to be heating up. The status of the spent nuclear fuel there is of greatest concern right now.

Currently, Japan ground self-defense force (GDF) helicopters are scooping water from the ocean and dropping it over the reactor, 7.5 tons at a time. The helicopters spraying water onto these reactors are protected by lead mats underneath, and the pilots are wearing protective suits and carrying dosimeters. In a press conference just now, a Japan nuclear safety agency official explained that the flights are limited to a certain minimum altitude, and no more than 40 minutes per helicopter per day, to limit exposure for pilots. The maximum permissible exposure level for Japan's self defense forces is typically 50 millisieverts; during this operation, the level has been raised to 100 millisieverts. When the pilots reach the limit, they have to leave. Normally, they would hover in one spot; given the extremely high risk of radiation exposure, they must move.

Given the dimensions of the spent fuel pools, and the fact that that not all the water dropped will actually make it into the pool, they will need to make hundreds of these water drop operations.

Tokyo police force water cannon vehicles carrying 4 tons of water at a time have also arrived at the Fukushima No. 1 plant. The water spray they shoot will target the storage pool that holds spent fuel rods; again, this is the focal point of grave concern at this time.

If these efforts fail and current conditions within the spent fuel pool continues, officials on NHK are saying the spent fuel rods in the storage pool would likely become more exposed and damaged, and release massive amounts of radiation into the atmosphere.

Responders are also urgently trying to restore the power supply, using power lines to run electrical lines to the location, so the plant's cooling system can be operated once again using sea water. It will take time to restore those capabilities, though, because the pumps have been damaged.

A Japan nuclear safety agency official is on NHK saying: "Regarding the No. 5 unit, the pressure is rising, and the water in the unit is decreasing. We have to prevent the same thing [fires/explosions] from happening in reactors No. 5 and 6. We have to secure the healthy conditions of the storage pools for units No. 5 and 6."

The live video NHK is airing of the helicopter water drops was shot 33km southwest of the plant. The winds in the area are currently are blowing to the southeast, toward the sea, and are expected to continue in that direction on Friday.

Below, the Institute for Science and International Security posts these images, with analysis, from DigitalGlobe: new satellite photos of the Fukushima Daiichi Nuclear site in Japan taken at 9:35AM local time on March 16, 2011. You can view the images in larger resolution at the Digital Globe site, and there is a PDF here with full Nuclear Facility Damage Analysis.

[In Fig. 1], damage to the Unit 1 reactor building from a previous explosion can still be seen. Damage to the Unit 3 reactor building from an explosion can be seen as well. Steam can still be seen emitted from the top of the damaged building. The angle of this new image, however, shows what appears to be more extensive damage to the Unit 3 reactor building than can be seen in previous satellite imagery. The image also shows damage to the reactor building for Unit 4 from an explosion. Steam can be seen venting out of a hole in the side of the reactor building for Unit 2. Workers likely removed a panel in the side of the building to vent the steam. Figure 2 shows the reactor buildings for Units 5 and 6. The side and roof of the buildings appear intact and there is no sign of steam venting from the building.

Figure 1. DigitalGlobe commercial satellite image of the Fukushima Daiichi nuclear site taken at 9:35AM local time on March 16, 2011.

Figure 2. DigitalGlobe commercial satellite image taken of the same site, showing reactor buildings for Units 5 and 6.

(thanks, @linmu)