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Explosion, fire at Fukushima nuclear power plant


The Los Angeles Times is reporting:

A day after responding to one of the worst earthquakes on record and a massive tsunami, the Japanese government sought to allay fears of a radioactive disaster at a nuclear power plant on the country's battered northeastern coast.

The outer walls of the Fukushima power plant's No. 1 reactor were blown off by a hydrogen explosion Saturday, leaving only a skeletal frame. Officials said four workers at the site received non-life-threatening injuries.

The inner container holding the reactor's fuel rods is not believed to be damaged, said Japan's Chief Cabinet Secretary Yukio Edano, and workers were cooling the facilities with seawater.

In a press conference shortly after the explosion, which left the facility shrouded in plumes of gray smoke, Edano explained that the reactor is contained within a steel chamber, which in turn is surrounded by a concrete and steel building. Although the explosion destroyed the building, it did not occur in the chamber.

"The escape of hydrogen mixed with the air between the chamber and the concrete-and-steel building and led to the explosion," Edano said.

"Tokyo Electric Power Co. has confirmed that the inner reactor is undamaged," he added. "There was no massive release of radiation."

This is indeed a dire situation, because if the engineers at the plant have lost control of the reactor, then it is only a matter of time before it enters a meltdown state -- if that hasn't already happened.  At this point there appears to be little that engineers can do, save for continuing to pour massive amounts of water on the exterior of the reactor structure and pray that its massively thick concrete and steel shielding can keep the reactor elements contained and radiation leaks to a minimum.

For those of you who are unfamiliar with the physics of a nuclear power plant, its primary component is a nuclear reactor, within which a low level, contained, and dampened nuclear chain reaction occurs.  The uranium fuel is packed into long rods, which are bundled together inside the reactor.  In order to manage the nuclear reaction and reduce it to a continuous, low level state, a system of "control rods" is also placed within the reactor.  These control rods absorb the neutrons that are released during the nuclear reaction, and through adjustments that allow them to absorb either a greater or lesser amount of neutrons, they can either slow down or speed up the reaction inside the chamber. 

The reactor is also filled with a liquid coolant that absorbs and dissipates the incredible amount of thermal energy that is released during the nuclear reaction.  In a nuclear power plant, this dissipated heat is used to heat water and produce steam that drives a system of dynamos connected to steam turbines.  In a nuclear engine (such as a submarine or aircraft carrier might carry) the steam is used to turn a series of steam turbines that drive the screws and operate the steering mechanism.

The cooling and dampening systems are critical to the safe operation of the reactor.  If either system is damaged, the state of the reactor cannot be properly controlled, resulting in either a runaway reaction (control rod malfunction) or an extreme heat situation (cooling system malfunction) that could reach levels high enough to literally melt the reactor -- a so-called "meltdown."  Under these extreme conditions, where control of the reactor is impossible, its safety mechanisms will certainly experience failure, potentially resulting in the release of large amounts of deadly radiation.

Thanks to lessons learned from over 50 years of nuclear power plant operation (specifically the accidents at Three Mile Island and Chernobyl) and the use of very sophisticated redundant safety systems and continuously improving construction and shielding technology, very few nuclear meltdowns have occurred, and the probability of a major meltdown occurring -- short of a natural disaster that heavily damages a reactor -- is very slim.

It will be equal parts fascinating and disturbing to watch how this episode is resolved.  It is extremely unlikely that anything resembling the massive radiation release at Chernobyl will be repeated at Fukushima.  The reactor at the Chernobyl plant was unshielded, and its safety systems were outdated and in disrepair (all typical of "Soviet engineering") while the Fukushima reactor is a textbook example of contemporary engineering and safety technology, with a sophisticated computer-driven reactor control system and a heavy, steel-reinforced concrete shield surrounding the reactor.

I am praying that the safety systems at Fukushima work the way they were designed, and keep both radiation leaks and damage to the most minimal levels possible.  I am also praying that this incident does not result in yet another decades-long chilling of public opinion over nuclear energy.  But we will simply have to wait and see what happens first.

__________________

Thanks to commenter DodoDavid for providing clarification on the operation of nuclear powered marine steam turbine engines.  The text above has been corrected.  
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Comments (13)

The reactor is als... (Below threshold)
Dodo David:
The reactor is also filled with a liquid coolant that absorbs and dissipates the incredible amount of thermal energy that is released during the nuclear reaction. In a nuclear power plant, this dissipated heat is used to heat water and produce steam that drives a system of dynamos connected to steam turbines. In a nuclear engine (such as a submarine or aircraft carrier might carry) the steam is used to compress the pistons that drive the screws and operate the steering mechanism.

The above-quoted paragraph needs clarifications.

The water inside a nuclear reactor is not itself converted to steam. Instead, the heat in the water is transfered to a secondary water system that contains steam generators. The generated steam is then directed via nozzles to the blades of steam turbines. The steam causes the turbines to spin. Being that the turbines are connected to electric generators, the spinning of the turbines causes the electric generators to spin, which results in the production of electricity.
On a nuclear-powered ship or submarine, the steam is not directed to pistons. The same turbines used to produce electricity are also used to drive the screws that propel the ship or submarine.

[Personal Note: I know these things because I am a graduate of the U.S. Naval Nuclear Power School, and the U.S. Navy trained me to work in the engine rooms of nuclear-powered ships and submarines.]

Dodo David,Thanks,... (Below threshold)

Dodo David,

Thanks, I should have remembered that nuclear powered marine engines are not boiler/piston types, but of course steam turbines.

Naturally my summary was pretty oversimplified. I appreciate your correction though.

The Fukushima units are all... (Below threshold)
jim2:

The Fukushima units are all BWRs, thus the water in the reactor is, indeed, converted to steam there and routed to turbines, etc.

We need thorium plants now.... (Below threshold)
BlueNight:

We need thorium plants now. The fuel is far cheaper and less weaponizeable, and the slurry-based design means it physically cannot melt down.

Ho hum.Yes, the po... (Below threshold)
Jim Addison:

Ho hum.

Yes, the potential exists for a contamination that will be expensive to clean up and take a long time, but it's hardly Armageddon. I am absolutely disgusted by Fox News on this - they have hyped this situation like carnival barkers, even as the experts they interview tell them to calm the heck down.

For instance, the radiation outside is "1000 times normal!" Run for your lives, right? Nope. At 1000 times normal, your body can still process it easily, with no harmful effects in the short OR long term.

For the record, too, neither Chernobyl nor Three Mile Island involved a meltdown. Allahpundit at Hot Air put a picture of a mushroom cloud on one of his stories about it. But you probably already knew AP is a completely drooling moron, right?

Sadly, both TMI and Chernob... (Below threshold)
jim22:

Sadly, both TMI and Chernobyl involved significant core damage. At TMI, there was some melting, but it mostly rubblized in the bottom of the vessel. Chernobyl most definitely was a total meltdown of the core.

Indeed, one need only google:

chernobyl elephant's foot

Considers the worst-case sc... (Below threshold)

Considers the worst-case scenario that the earthquake, tsunami and explosion damaged the containment system:
At this point, events in Japan bear many similarities to the 1986 Chernobyl disaster. Reports indicate that up to 1.5 meters (4.9 feet) of the reactor fuel was exposed. The reactor fuel appears to have at least partially melted, and the subsequent explosion has shattered the walls and roof of the containment vessel — and likely the remaining useful parts of the control and coolant systems.
And so now the question is simple: Did the floor of the containment vessel crack? If not, the situation can still be salvaged by somehow re-containing the nuclear core. But if the floor has cracked, it is highly likely that the melting fuel will burn through the floor of the containment system and enter the ground. This has never happened before but has always been the nightmare scenario for a nuclear power event — in this scenario, containment goes from being merely dangerous, time consuming and expensive to nearly impossible.

Chernobyl was also nearly a... (Below threshold)
ikkonoishi:

Chernobyl was also nearly a case of intentional sabotage under the guise of running a "test". It was like testing the responsiveness of the fire department by throwing molotovs at a gas station, or seeing if bees are Africanized by punching the hive.

The test the Chernobyl oper... (Below threshold)
jim2:

The test the Chernobyl operators intended to run was not quite as bad as that.

The problem was more that they conducted the test without the proper initial conditions. That is, they were supposed to run the test, and would have to report that they failed to run it. Instead of doing that, they decided to do the test anyway, perhaps believing that the differences were not too great.

That reactor design in inherently unstable, and so is not forgiving. The operators knew that, but still thought things would be okay.

They were wrong.

To borrow your bee hive analogy, they thought the hive was empty.

And, as I said, they were wrong.

Many of those decision-makers died, so it was culpable ignorance rather than deliberate.

Just so everyone is clear o... (Below threshold)

Just so everyone is clear on this, the Chernobyl accident was absolutely a total meltdown of a nuclear reactor core.

At the Chernobyl plant, the main turbine generators supplied the power that ran the electric water pumps in the reactor's cooling system. There was a backup electrical system comprised of diesel generators, but it took 65 - 70 seconds to bring it online. The meltdown was the result of a test, whereby the steam to the main turbines was to be cut off and the turbines allowed to "freewheel" -- turn only under the power of their own inertia -- in order to determine if the freewheeling turbines still provided enough electricity to bridge the 70 seconds necessary to bring the backup electrical system online.

Unfortunately, through a combination of reactor design flaws, faulty equipment, and errors in judgment, the reactor was allowed to drop to a near shutdown level as it was being powered down in anticipation of the steam cutoff. When engineers tried to bring the reactor back up, they brought it up too quickly by removing nearly the entire length of control rods and increasing the circulation of the cooling water, resulting in dangerous internal conditions within the reactor.

The test went on as scheduled anyway, but the reactor was in a highly unstable state. Because the test necessarily resulted in a decreased rate of water flow due to powering down the turbines, steam voids developed within the reactor. The steam voids hampered the ability of the water to cool the reactor, which resulted in more heat and more steam. This destructive feedback loop over-pressurized the reactor, causing it to explode. When the superheated reactor components were exposed to outside air after the explosion, a massive fire erupted.

Engineers tried to initiate an emergency shutdown, but the instability of the system prevented them from ever regaining control of the reactor. The reactor core melted and the resulting 'corium' flowed through the structure under the reactor. After the accident, a giant blob of corium resembling an elephant's foot was discovered. Evidence of a brief 'nuclear excursion' -- a limited continuation of the nuclear reaction -- outside of the reactor core was also present.

Another important aspect of the Chernobyl accident and the resulting cataclysmic release of radiation, was that the reactor had no shielding around it. All modern nuclear reactors have a "sarcophagus" of steel-reinforced concrete up to 2 meters thick surrounding them. That measure alone will greatly limit the risk of radiation leaks, if/when a meltdown actually occurs.

In your first post describi... (Below threshold)
J Reinhart:

In your first post describing the type of power plant in question I would like to suggest that the author Mr. Dodo David learn the difference between a BWR (Boiling Water Reactor) and PWR (Pressurized Water Reactor). Mr. Dodo correctly described a submarine reactor as a PWR but the plant in question is a BWR. In a BWR the primary coolant is actually boiled and sent to the turbine generator, condensed and returned to the reactor. The aforementioned fact concerning BWR's makes it a little more difficult to work on a BWR's turbine system during outages because the entire turbine system exposed to the steam becomes slightly radioactive.

News are also circulating i... (Below threshold)
dian:

News are also circulating in the Philippines that radiation will most likely hit the country, mostly caused by Japan winds being blown off to the country. Any news about that? The people are somewhat scared and we are all hoping and crossing our fingers that this really is just a hoax.

http://randomthoughtsinabox.blogspot.com/2011/03/fukushima-nuclear-power-plant.html

What is burning at the nucl... (Below threshold)

What is burning at the nuclear reactors in Fukishima? The media is talking about "fires" but never describes what is burning? Is this a typical fire (like a house or camp fire) or are we talking bout the reactor rods or some other material?




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