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Two plants near Tokyo, each with multiple reactors are on the verge of meltdown after emergency backup cooling was shut down by loss of power due to flooding.  (Source: CNN)

An explosion damaged the roof of one plant, releasing radiation on Saturday.  (Source: Reuters)

The plants lie within the Tokyo metropolis. People are being evacuated from within a 20 km radius.  (Source: CNN)
Japanese nuclear disaster is cause for pause, reflection

The Sendai Earthquake struck Japan early Friday morning with unrelenting fury.  Measuring 8.9 to 9.1 Mw-megathrust the quake was among the five most severe in recorded history and the worst quake to hit Japan.  In the aftermath of this severe disaster, as the nation searches for survivors and contemplates rebuilding, an intriguing and alarming storyline has emerged -- the crisis at the Fukushima Daiichi nuclear plant.

You may recall that a few years back Japan was struck by another quake which cracked the concrete foundation of a nuclear plant, but yielded virtually no damage.

By contrast, this time the damage was far worse, creating what could legitimately be called a nuclear disaster.

I. Fukushima Daiichi - a Veteran Installation

The Tokyo district of Fukushima is home to two major nuclear power installations.  

In the north there is the Fukushima "Daini" II plant, which features four reactors -- the first of which went online in 1982.  These units produce a maximum of 4.4 GW of power and are operated by the Tokyo Electric Power Company.

To the south lies the Fukushima "Daiichi" I plant, a larger and older installation featuring six reactors, the first of which went online in 1970.  Operated by Tepco, the installation offers a combined 4.7 GW of power.  It was here that disaster struck.

II. Disaster at Fukushima Daiichi 1

While the southern installation is over four decades old, Japan has been responsible in retrofitting the plant with modern safeguards.  Among those is an automatic switch which shuts off the reactor when an earthquake struck.

The switch performed perfectly when the quake hit Friday morning, shutting of the three reactors that were active at the time.  Control rods lowered and the reaction stopped.

The next step was the cooling the power rods, composed of uranium-235, to prevent them from melting.

Cooling water was pumped over the rods for about an hour, but before the rods could be fully cooled, stopping the reaction, the pumps failed.  According to the International Atomic Energy Agency, and multinational oversight group, the failure was due to failure in the backup generators due to the tsunami flooding.

On Saturday Japanese authorities and power officials tried to use sea-water injections to complete the cooling process, but those plans were stalled when another tsunami warning arrived.

An explosion occurred inside at least one of the reactor buildings.  It is believed to be due to the build-up of pressure after the pumps failed creating hydrogen and oxygen gases, which subsequently combusted from the heat.

Malcolm Grimston, Associate Fellow for Energy, Environment and Development at London's Chatham House told CNN:

Because they lost power to the water cooling system, they needed to vent the pressure that's building up inside.My suspicion is that as the temperature inside the reactor was rising, some of the metal cans that surround the fuel may have burst and at high temperature, that fuel cladding can react with water to produce zirconium oxide and hydrogen.

That hydrogen then will be part of the gases that need to be vented. That hydrogen then mixes with the surrounding air. Hydrogen and oxygen can then recombine explosively. So it seems while the explosion wasn't directly connected with the nuclear processes, it was indirectly connected, because the hydrogen was only present because of what was going on in the reactor core.

The explosion damaged the roof of the plant and sent billows of smoke up into the air.  According to officials some radioactive material was released into the atmosphere.  Outside the plant perimeter, levels of radiation measured 8 times higher than normal.

Meanwhile reactors at the newer Fukushima II are also beginning to heat up after their own cooling systems failed.

Japanese officials have evacuated people from an expanding radius around the plants as a precaution.  Currently the evacuation zone is at almost 20 km.  They hope to try to continue cooling, but have to work around tsunami alarms from earthquake aftershocks that have continued into Saturday.  U.S. Secretary of State Hillary Clinton has announced that the U.S. is sending high-tech coolant to the plants, in and attempt to avert disaster.

III. Can a Meltdown be Avoided?

Without proper cooling, the rods will continue to heat and proceed towards meltdown, releasing clouds of radioactive gas.  The first question is thus whether meltdown can be avoided.

At the Fukushima I plant, radioactive cesium was discovered.  Cesium is in the beta decay chain tellurium -> iodine -> xenon -> cesium.  Its occurs roughly 16 hours after an unchecked uranium reaction and its presence indicates that one of the fuel rods may already have melted down.

Once one rod melts, it will be much more difficult to prevent the others from melting down as well.

According to reports, the coolant temperatures inside the reactor have exceeded 100 degrees Celsius.  If they reach 540 degrees Celsius the fuel rods will fully melt down.

The question now becomes what to do.  

According to reports by Nippon Hoso Kyokai (Japan Broadcasting Corporation), three individuals have already been exposed been the victims of radiation poisoning (likely plant workers) and that radioactivity levels at the plant have risen to 1,000 times the normal levels at the plant control room.

One option on the table is to vent the reactors, allowing them to blow off the steam and prevent a greater buildup of pressure and heat.  However, doing so could release significant levels of radioactivity into the surrounding area.

The alternative is to try last ditch cooling and hope that if the rods do melt, that the secondary containment will hold.  The release of radioactive gases from venting would pale to that if the secondary containment was breached.  Such a scenario would likely result in the modern day equivalent of Chernobyl.

Whichever course of action is selected, there's a great deal of risk of radiation exposure to those who inhabit the area in the near future.  States James Acton, international physicist, in an interview with CNN, "There's a possibility of cancer in the long term -- that's the main hazard here."

IV. Grim Lessons From the Disaster

At Three Mile Island, the U.S. learned the hard way not to put vital controls in the hands of plant operators.  Operators almost created a meltdown, when they accidentally disabled necessary cooling.  That was due to the poor quality of indicators. 

As the result, the nuclear community learned to automate shutdown processes.

Ultimately the Fukushima disaster illustrates the need for sealed backup generators.  The containment procedures in all their modern glory are useless if the backup power goes out.  And, if possible, it shows that it is desirable to build new nuclear plants farther from the sea and from fault lines (though this could cause costs to increase).

As the fight to avert meltdown plays out, the final damage won't be known for weeks to come.  But the international community is already reacting.

At this time it's vital not to overreact to this worse case scenario.  

The disaster does illustrate that nuclear fission power is far from failsafe, particularly older reactors -- even if retrofitted with modern controls.  Ultimately the international community needs to work towards fusion power, which should be much safer and cheaper.

At the same time, it's important to consider that there's a great deal of background radiation released from the burning of fossilized coal and that mining fossil fuels has led to many a great loss of life and resources as illustrated by recent coal and oil disasters.

And nuclear power is far less expensive than solar or wind power in base costs, and generally less expensive even after all the red tape that increases plant creation costs by an order of magnitude in the U.S.

There's no easy answers here.  Oil and coal power emit dangerous nitrogen and sulfur-containing gases and carbon dioxide into the ozone.  And their fuel is dangerous to obtain.  But they're cheap.  Solar and wind power are relatively safe, but they're expensive and offer inconsistent power.  Nuclear power is cheap and produces no emissions normally, but it can be a danger in the case of natural disaster or malicious attack.

It's important not to turn a blind eye to this disaster, but it's equally important not to overreact.


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Some Clarifications
By randomly on 3/12/2011 11:01:29 PM , Rating: 5
As was pointed out these reactors were all immediately shut down upon quake detection by the safety systems. There is essentially no fission reactions going on to produce heat, nor is there any chance that the core will go critical again.

The only source of heat is all the short lived radioactive fission products that have built up in the fuel during months of operation. When you first shut the reactor off, the heat output almost immediately drops to about 10% of what it was. This 10% is just from the decay energies of the radioactive fission products. A lot of these fission products have very short half lives, so the heating power drops off rapidly over the next few hours. Getting rid of the decay heat becomes easier and easier as time goes by since the amount of decay heat continues to diminish.

There is no chance at this point for anything like a Chernobyl explosion. I'll be surprised if anybody at all dies from this.

The explosion was described as a hydrogen explosion. Almost certainly this is the result of the Zirconium cladding inside the reactor core getting too hot and reacting with steam to produce Hydrogen gas. Since they lost power to pump coolant to cool the core, the water in the reactor continued to heat up. The hotter the water, the higher the pressure in the core. To reduce the pressure they vent off steam from the core, this carries a lot of heat out of the core. Unfortunately it means you are boiling water away out of the core and the water level will drop. If it drops too far the top of the core will be uncovered and the tops of the fuel rods can melt.

This very likely is what happened. The melting rods contaminated the core water with cesium-137 and other isotopes and this was vented into the atmosphere along with the steam being vented.The Hydrogen from the Zirconium/Steam reaction was also vented into the secondary containment structure. The hydrogen igniters probably weren't working due to power failure so the hydrogen built up. At some point it was ignited by something and the explosion occurred that we see on TV.

The Fukushima Daiichi reactor #1 is a 40 year old boiling water reactor design. It was scheduled to be retired in only one more month.

It seems clear at this point that the reactor is ruined and will never operate again. It may be somewhat more expensive than normal to decommission the damaged plant.

As a comparison - a modern Gen III+ reactor like the AP1000 has passive cooling systems that need no power, no backup generators or anything, to operate, and the reactor will be fine on its own for 3 days before requiring any operator intervention. Even then it only needs water to be added.




RE: Some Clarifications
By Scabies on 3/13/2011 3:21:20 AM , Rating: 2
you, sir, deserve an internet. I'd rate you up if I hadn't already commented. Too bad the reporting agencies like saying things like Cherynobyl and Meltdown. Might I append an outcome:

If a partial meltdown has occurred, TEPCO will be forced to take the Three Mile Island approach: cool it later, seal it, leave it. Verifying this may be dangerous and expensive, so they might end up doing it anyways since the reactor is at the end of its lifetime.

An investigation will be opened to catalog the events in sequence, and determine the best way to avoid such a "disaster" (because I didn't want to use "event" twice) in the future. This will likely center around a better backup, like high output mobile generators that can be airlifted or chopper'd within the lifetime of the backup batteries. Unless something weird happens like a structural collapse or a large explosion within the reactor, it will be found that although some radioactive product was released (voluntarily, to prevent a steam explosion), the terminal fail-safe, being the containment vessel, worked as intended.

Structural analysis of the other reactor buildings will lead to better earthquake/tsunami resistant designs, or will become the high water mark (morbid pun) if everything ends up intact since this involved a top-ten-ever earthquake.

News agencies will continue to use push-button words that stir up anti-nuclear sentiment in the ill-informed, because it makes good press.

US politicians will try to get their opinions in for brownie points and face time.

Wikipedia will be the victim of a flood of edits and pageviews to this and other nuclear events.


RE: Some Clarifications
By CoreGamer on 3/14/2011 2:10:13 PM , Rating: 2
I have to point out a flaw in your comment. The problem is not that the heat will continue to rise and spiral out of control. The problem is that the cooling system has failed completely; so that ANY amount of residue heat, (even if it would have been easily manageable before) is now a serious problem. As somebody else pointed out in a great comment above, there are real problems that could arise from a meltdown, which can (and might) happen unless they figure out a way to get enough power and coolant to the plant.


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