The crisis at Fukushima Daiichi nuclear power plant has yielded the top news spot to the events in Libya for now, but it’s far from over. “Factually, the problem in Japan is only just starting, ” Sebastian Pflugbeil, a physicist and president of Gesellschaft für Strahlenschutz (Society for Radiation Protection, Germany) is quoted by German magazine Focus.

To secure Fukushima Daiichi, a total of 3 reactor cores (1, 2 and 3) and 4 spent fuel pools (1, 2, 3 and 4) need to be brought permanently under control. If any one of these cores or spent fuel pools goes into full melt down, high levels of radiation from destroyed fuel rod assemblies may pollute the reactor site so much that staff will be forced to indefinitely abandon the entire plant, including control rooms and cooling equipment of units currently in a semi-controlled state.

On Tuesday Tepco reconnected power to the damaged reactor blocks in Fukushima Daiichi, but it is still a long step from being able to turn on lights in control rooms to actually running massive cooling pumps in the damaged plant.

Keith Bradsher writes in the New York Times:

Preventing the reactors and storage pools from overheating through radioactive decay would go a long way toward limiting radioactive contamination. But that would require pumping a lot of cold freshwater through them.

The emergency cooling system pump and motor for a boiling-water reactor are roughly the size and height of a compact hatchback car standing on its back bumper. The powerful system has the capacity to propel thousands of gallons of water a minute throughout a reactor pressure vessel and storage pool.

These pumps first need draining of air pockets to be able to be operated again, which is a difficult process under ordinary conditions, when the core isn’t damaged yet and radioactivity in the water of the primary cooling cycle is relatively low. Now the risks to the technicians will be tremendous.

It has also been reported that the pumps in unit #2 are no longer usable and replacements have been ordered. Any effort to remove the dead pumps, move in new pumps and reconnect them to the piping is going to be a real challenge under current conditions.

A couple of days ago the first reports came in of low doses of radiation in drinking water in Tokyo, then still around 1% of legal limits. That was after winds for the first time since the accident had blown south from Fukushima towards the Kanto area, the flat plain surrounding Tokyo. Later they turned back out towards the sea.

This week the winds from the north returned. Radiation levels in drinking water in Tokyo that exceed Japanese legal limits for infants below one year old have now alerted many to the risks. Tap water should no longer be used to mix with infant formula, but stores have run out of bottled water. What are mothers going to do? Boiling does not destroy radioactivity. Tokyo gets much of its drinking water from dams in the mountains west of the city, such as Lake Okutama, which get replenished by rain.

The Kanto plain is home to about as many people as live in Canada, California or Spain. What are they going to do without safe drinking water?

For lack of available fresh water, sea water has been used for cooling at Fukushima for almost two weeks now. Each ton of sea water contains about 35 kg of salt, which stays behind when the water boils off or evaporates as steam. Gradually the inside of the reactor cores and storage pools will become silted or encrusted with solid salt. Sooner or later the efforts to cool the reactors won’t be sustainable without ample supplies of fresh water.

Time is running out in Fukushima.

See also:

• New Problems at Japanese Plant Subdue Optimism (NewYork Times)
• Status update by Gesellschaft für Reaktorsicherheit (in German)

Today’s magnitude 8.9 earthquake 400 km from Tokyo was not business as usual. The Japanese are well prepared for quakes and building standards are high, but this quake is the strongest since scientific measurements have been available. It was shaking powerfully even here in Tokyo, for what felt like minutes on end. Numerous items fell of shelves, most of my wine glasses are now a pile of shards — and this is several hours by car away from the centre of the quake. We’ve had countless aftershocks for several hours now.

I was alone at home when it happened and have not been able to make mobile phone calls or send SMS to reach my other family members, though my wife and I could communicate by Skype chat (she has an iPhone). I know all the trains are stopped right now, with people walking for kilometers to get home on foot, as did my wife.

The images of tsunami devastation near Sendai are shocking. A refinery is on fire in Chiba prefecture near Tokyo. I wonder how many people will have lost their lives in the tsunami and in collapsed buildings.

UPDATE (2011-03-12 05:38 JST):

All members of my family got home OK. We were watching TV news until 01:30 in the morning. I got many emails, phone calls and Skype chats from concerned friends and relatives.

Several mentioned the serious technical problems in the Fukushima Daiichi nuclear power station. While the government announced an evacuation of people living within 3 km of the station, few details of what was going on were provided. From US and German media reports I hear that both mains power and backup generators are out and that the cooling system seems to have a leak. Tokyo Electric Power Corporation (TEPCO) was trying to connect external power generators. There was talk about releasing steam that had built up to 50% more pressure than the reactor was designed for. Without adequate cooling the reactor core could melt even when shut down due to nuclear decay heat that continues at about 7% of regular power output when the reactor is shut down. The backup diesel generators were not working due to flooding by the tsunami.

UPDATE (2011-03-12 15:20 JST):

The decision to vent the containment vessel of unit 1 of Fukushima Daiichi suggests that efforts to get the main cooling system back online have not been successful, as it reflects excess temperatures of cooling water and heat buildup.

The Tokyo Electric Power Company (TEPCO) has announced it will “implement measures to reduce the pressure of the reactor containment vessel for those units that cannot confirm certain level of water injection by the Reactor Core Isolation Cooling System, in order to fully secure safety.”

(allthingsnuclear.org)

The Reactor Core Isolation Cooling System is a mechanical system to pump cold water to cool the reactor core using a steam turbine driven by boiling coolant water. It does not rely on outside A/C power for the pumps, but needs at least battery power to open and close valves. It is the last line of defense should both grid power and backup power be lost. Without the above mentioned water injection, water levels could fall in the reactor core and the fuel elements could overheat and partially melt, as in the Three Mile Island accident near Harrisburg, Pennsylvania in 1979.

See also:

• Containment at Fukushima
• Japan Orders Evacuation Near 2nd Nuclear Plant

UPDATE (2011-03-12 22:20 JST):

The cabinet secretary said that the explosion at Fukushima Daiichi #1 power station was a hydrogen explosion. When they released excessive pressure from inside the containment vessel, it contained hydrogen, which mixed with air in between the exterior wall and the containment vessel, and ignited. That blew away the outside wall. Four workers were injured and have been hospitalized.

The hydrogen is assumed to be the result of a reaction between steam and overheated zirconium cladding of the fuel rods. The water level in the reactor must have dropped so far that the top of the rods was no longer immersed in water and became red hot. The zirconium stripped oxygen from water (H2O) which releases hydrogen. If you remember the Three Mile Island accident in 1979, that was the same way the hydrogen bubble was produced in the TMI incident. The fuel rods then melted into a blob, but the restored cooling managed to contain the molten fuel inside the reactor core.

Since all attempts to restart the cooling pumps have failed, the reactor operators are now planning to pump sea water into the reactor vessel to cool the pressure vessel inside. The choice of sea water appears to be dictated by a lack of fresh water on site. Normally one would avoid salt water because of its corrosive effects, but the operators realize that this 40 year old reactor will never be repaired or put back into service again. It’s a wreck and they do all they can to stop its spent fuel from being melted and released.

An area of about 160 square kilometers that lies within 20 km of Fukushima Daiichi or 10 km within Fukushima Daini along the Pacific coast is going to be evacuated.