21 Mar 2011: Analysis

Anatomy of a Nuclear Crisis:
A Chronology of Fukushima

The world’s worst nuclear reactor mishap in 25 years was caused by a massive natural calamity but compounded by what appear to be surprising mistakes by Japanese engineers. The result has been a fast-moving disaster that has left officials careening from one emergency to the next.

by david biello

On March 11, the ground beneath Japan swayed for as much as 5 minutes, a 9.0-magnitude earthquake that ultimately moved Japan some 2.4 meters (7.9 feet) closer to the United States. Thirty minutes later, a wall of water roughly 250 miles long slammed into the northeast coast of the island nation, smashing everything in its path. Among the victims were at least 7,000 dead and 10,000 missing — as well as one nuclear power plant: Fukushima-Daiichi and its six reactors.

In the ensuing days, the world has watched as Japanese engineers and plant workers have struggled to keep the fuel rods inside the crippled Fukushima plant from melting down, lurching from one crisis to the next as four of the complex’s reactors have experienced explosions and releases of radioactive material. Amid the confusion, it was clear that some very basic mistakes — most noticeably placing backup diesel generators only slightly above sea level in a tsunami zone — had made the situation at Fukushima far worse.

Even now, 10 days after the crisis began, the situation at Fukushima is still not under control. The disaster is clearly worse than the 1979 partial meltdown at Three Mile Island in Pennsylvania, yet not as grave as the 1986 explosion at the Chernobyl nuclear plant, which spread radioactive material over large portions of Europe. A chronology of how the Fukushima crisis has unfolded demonstrates that even a country as advanced as Japan — and as practiced in dealing with natural disasters — was unprepared for an earthquake of this magnitude, the largest in Japan in 1,200 years.

March 11

When the earthquake struck at 2:46 p.m., the Fukushima-Daiichi nuclear power plant, along with at least three others, automatically shut down, sliding control rods — made of materials, like boron, that block neutrons — into the three reactor cores that had been up and running. That instantly stopped the fission of the enriched uranium fuel that allows a nuclear reactor to produce the steam that spins a turbine to make electricity.

But even with fission stopped, nuclear fuel rods must be kept cool, as byproducts of the nuclear reaction continue to break down and produce heat for years. The key to cooling the rods is simple: flow water past them.
The now-still water in the reactors began to boil off, threatening a meltdown of the uranium inside.
But because of the earthquake, no electricity could be delivered to the Fukushima-Daiichi nuclear power plant to run the cooling pumps. The back-up diesel generators that should have kicked in when power was lost did not survive the tsunami, which easily overtopped the seawall protecting the plant — leaving only batteries to run all the systems. At the same time, the tsunami flooded critical electrical equipment. After eight hours, the batteries went dead — meaning the nuclear power plant had no electricity, and no way to cool itself.

In essence, the now-still water inside the reactors began to boil off, exposing the fuel rods and threatening a meltdown of the uranium fuel pellets inside.

By the evening of the first day, the Japanese government warned of cooling problems at the nuclear power plant and declared a “state of nuclear emergency,” though stressing that no radiation leaks had been detected. Nevertheless, government officials advised people living within a few kilometers of the plant to leave. At the same time, portable diesel generators brought to the Fukushima-Daiichi plant restored power to some systems, although it is unclear why more generators weren’t put into service to cool the reactors. By later that night, the Japanese government noted that radiation levels appeared to have risen in at least one of Fukushima’s reactors.

March 12

In the early hours of Saturday, March 12, the nuclear power plant’s owner and operator, Tokyo Electric Power Co. (TEPCO), reported rising pressure inside reactor No. 1, a sure sign that not enough water was reaching the core, allowing steam to build up. In fact, pressure readings reached 840 kiloPascals at Fukushima-Daiichi reactor No. 1 — more than double normal operating pressures. By dawn, pressure was also rising at another nearby nuclear power plant disconnected from the grid by the quake and tsunami — Fukushima Daini, with four reactors. But backup power there seems to have prevented further trouble.

That morning, TEPCO workers began venting radioactive steam at Fukushima-Daiichi reactor No. 1 to prevent pressure from getting any higher and bursting the thick steel vessel that holds the nuclear core. In essence, the operators moved radioactive gases from the inner containment area into the larger building that houses the reactor. At the same time, the government began evacuating some 20,000 people from the region within 10 kilometers of the stricken power plant.

Fukushima Japan Nuclear Reactors
AFP/Getty Images
On March 12, an explosion tore the roof off the building housing reactor No. 1 after workers vented high-pressure steam and hydrogen into the structure.
Without the ability to add more water due to pump failures, however, the fuel rods could not be cooled. Such nuclear fuel rods are encased in a hard zirconium cladding, which holds them together and allows the neutrons necessary for fission to pass through. But when the fuel rods are not cooled, that same cladding swells and cracks, allowing the release of radioactive particles produced by fission, such as cesium-137 or iodine-131. Worse, as temperatures rise as high as 1,200 degrees Celsius, the cladding strips oxygen from the surrounding steam — like high-speed, high-temperature rusting — leaving hydrogen gas behind.

When workers vented the high-pressure steam and hydrogen into the building housing reactor No. 1, it began to build up. At sufficient concentrations — roughly 4 percent or more — hydrogen is explosive if it finds oxygen or a spark. That is exactly what happened at reactor No. 1, where an explosion tore the roof off of the building housing the reactor. Four workers were injured.

But by nightfall, as pressure continued to swell, TEPCO workers began to pump seawater and boric acid into reactor No. 1 via lines put in place to put out fires. It was a desperate bid to cool the reactor and ensure that fission did not resume. The Japanese government began distributing iodine pills to nearby residents in an effort to ensure that any radioactive iodine released did not end up inside the thyroid glands of citizens.

March 13

By the morning of March 13, the Japanese government’s evacuation efforts had expanded to include a full 20-kilometer radius around the plant, putting more than 100,000 people on the move. Radiation levels in Fukushima-Daiichi nuclear power plant had risen above safe limits. TEPCO expanded its seawater and boric acid pumping efforts to include reactors No. 2 and No. 3 — meaning cooling was now failing at all three nuclear reactors in operation at the time of the earthquake. The workers continued to vent radioactive steam.

March 14

On Monday morning, March 14, another hydrogen explosion ripped reactor No. 3 at 11:01 a.m. local time, injuring seven workers and four soldiers. One of the soldiers may have ingested radioactive material and was transported to the National Institute of Radiological Sciences. The explosion tore open the building housing reactor No. 3 and caused its pressure readings to fluctuate, raising fears that its steel containment vessel might be cracked, according to NISA. Pressure readings quickly returned to normal, however, easing those fears, though water levels were as much as 2.3 meters below the top of the 3.7-meter-long fuel rods.

By nightfall, cooling had completely failed at reactor No. 2, potentially exposing the entire fuel rods in that reactor to the air and steam. To prevent another hydrogen buildup and explosion, TEPCO workers cut a hole in the side of the building housing Unit 2.

March 15

By Tuesday morning, March 15, another explosion was heard coming from the building housing reactor No. 2. Steam rose from the damaged building and radiation levels at the power plant increased four-fold. Worse, this explosion potentially damaged part of the core containment system — a donut-shaped tube of water meant to both cool the reactor in an emergency and capture any radioactive particles. The so-called suppression pool might now have a leak, allowing radioactivity to escape — a problem the U.S. Atomic Energy Commission had identified in the design of this reactor as far back as 1972. Atmospheric pressure dropped from three times normal to normal in an instant after the explosion. And radiation levels spiked to 965.5 microSieverts per hour in the wake of the blast, suggesting some radioactive material might be escaping from the reactor.

Fukushima Japan Nuclear Reactors
AFP/Getty Images
A specialist from Tokyo Electric Power Co uses a diagram to explain the structure of the Fukushima-Daiichi plant on March 15.
That same morning, a fire broke out in the building that houses reactor No. 4, which contained spent fuel rods and had been shut down for maintenance even before the earthquake struck. Those rods, submerged in a concrete and steel tank filled with boric acid, need to continue to cool until they can be transferred for either reprocessing or storage in massive concrete and steel casks. The spent rods also began to heat up when cooling systems failed.

As a result of the danger posed by radioactive particles wafted into the air by the smoke, Prime Minister Naoto Kan, in a televised address, warned residents living within 30 kilometers of the failing nuclear power plant to remain indoors.

Another hydrogen explosion tore two holes, roughly eight meters across, in reactor No. 4’s outer building. U.S. Nuclear Regulatory Commission Chairman Gregory Jaczko suggested in testimony to Congress on March 16 that the pool was actually dry — meaning the overheating fuel rods were exposed to the air.

By nightfall, radiation levels reached 400 milliSieverts an hour near reactor No. 3. As a result of those elevated radiation levels, TEPCO evacuated all non-essential personnel — some 750 workers — leaving a skeleton crew of 50 to continue desperate efforts to manually pump seawater and boric acid into the stricken reactors. Even those left behind had to evacuate the control room for reactor No. 4 because of increased radiation levels.

March 16

Wednesday, March 16, dawned with thick white steam billowing from the damaged building that housed reactor No. 3, suggesting that the spent fuel pool in that building was boiling off its cooling water as well. And yet another fire broke out in the building housing reactor No. 4.

Still, temperature and pressure began to come down at reactor No. 2, suggesting the workers’ valiant efforts were having an effect there. By nightfall, continued pulses of radiation required the workers to pull back from such efforts — and a planned helicopter flight to drop seawater on the power plant had to be postponed.

Tests showed no radioactive cesium or iodine in local water supplies. The final two reactors — No. 5 and No. 6, the only reactors to show no signs of trouble — appeared to be staying cool. But radiation levels next to the
Flitting like ghosts through the stricken plant, workers struggled to bring cooling water to the boiling reactors.
reactors remained high, although radiation levels at the boundary of the stricken nuclear power plant were relatively low — roughly three times normal background radiation for a year.

The Japanese military began dropping seawater from two helicopters onto the exposed fuel pools at reactors No. 3 and No. 4. And water cannons vaulted cooling liquid into the spent fuel pools to good effect, according to TEPCO.

But pressure also began to rise again at reactor No. 3. And water levels remained too low in all three reactors operating at the time of the earthquake. The potential remained for a full meltdown — when all the fuel rods melt and flow to the bottom of the containment building, potentially causing a steam explosion that would release radioactive materials — to occur.

March 17-20

Over the past several days, Fukushima-Daiichi workers continued their heroic efforts, facing further explosions or invisible hydrogen fires and dangerous levels of radiation. Given an inability to either shield themselves or remain far from the sources of that radioactivity, the workers could only protect themselves by limiting the amount of time spent in highly radioactive areas. Flitting like ghosts through the stricken nuclear power plant and breathing through special tanks and filters strapped to their backs, the skeleton crew of workers struggled to bring cooling water to the boiling reactors and the overheating pools of spent fuel.

Over the weekend, engineers continued to battle problems, such as a buildup of pressure in reactor No. 3. In addition, the Japanese government reported that milk, canola, spinach, and other agricultural products from regions near the plant contained elevated levels of radioactive elements, further heightening fears among the Japanese public. The government barred shipments of these products from the affected prefectures.

MORE FROM YALE e360

Japan’s Once-Powerful
Nuclear Industry is Under Siege

Japan’s Once-Powerful Nuclear Industry is Under Siege
The disaster at the Fukushima-Daiichi nuclear power plant has highlighted the importance of nuclear energy to Japan and the power long wielded by the nuclear sector. But that influence now is sure to wane, to the relief of opponents who have fought for years to check nuclear’s rapid growth, writes Caroline Fraser.
READ MORE
Now, perhaps the best hope may be the completion of a new power line, which would bring much-needed electricity from power plants outside the area to restart the electric pumps to cool down the reactors. That progress has been slowed both by the damage from the earthquake and tsunami to the grid in general, but also by the high levels of radiation at the reactor buildings, where the line would need to be connected. Pumps and other safety systems may also have been damaged in the earthquake, tsunami, or subsequent meltdown prevention efforts. Those challenges were evident on Monday. Even after connecting a mile-long, high-voltage transmission line to reactor No. 2, engineers said they still had not succeeded in getting the reactor's electrical systems and water cooling pumps to work. The Japan Atomic Industrial Forum estimated that fuel rods remain exposed inside all three reactors in operation at the time of the earthquake.

Fukushima-Daiichi is unlikely to return to generating electricity via fission. Instead, it may become a memorial like Chernobyl, an entombed emblem of a terrible nuclear accident. And radioactive elements, like cesium-137, with a half-life of 30 years, will remain in the plant’s environs for years to come, a reminder to the region’s residents of the tsunami and its devastating blow to Fukushima.

POSTED ON 21 Mar 2011 IN Business & Innovation Energy Policy & Politics Policy & Politics Pollution & Health Pollution & Health Science & Technology Asia North America 

COMMENTS


Thanks: Very well written and gives a great insight into the sequence of events.

Posted by John on 21 Mar 2011


It's really surprising that the dg sets were flooded and failed. Anyway, getting the transmission lines erected in the shortest possible time is the only way out. a very good explanation.

Posted by satish tiwari on 21 Mar 2011


I have read many comments on the Fukushima Daiichi nuclear plant disaster...and each one attributes the disaster to the Japanese engineers..while it is my understanding these 6 reactors were GE technolgy and design...and a Fajima/GE construction consortium....Albeit a 40 year operating record is not too shabby..and a record earthquake/tsunami will screw up a good day.. but should not all the problems of backup systems, containment bldgs and storage, water levels and spent storage, etc...be an unfair comment to Japanese engineers.

Posted by deryk anderson on 24 Mar 2011


I have just come across this interesting description of the sequence of events at Fukushima Daiichi. I have a slightly different version as regards the back-up diesel generators which, after the author, did not survive the tsunami. From what I know, diesel generators are installed in a special annex connected to the reactor building: both these buidings are practically watertight and located away from the seashore. Apparently the diesel generators survived the tsunami: what did not survive was the equipment for the seawater intake for the emergency cooling, installed in a large concrete pit close to the seashore and protected by a seawall which was easily overtopped by the tsunami.


Posted by carlo mancini on 03 Apr 2011


You delineate the sequence of events, more or less. But you make no mention of what the Japanese engineers made during the battle to keep the reactors from going into meltdown. You praise their tireless efforts. So, did they do something wrong, or not? What are the surprising mistakes, exactly?

The only criticism you had was of the placement of the backup generators prior to the earthquake on Mar 11. Surely you can do a better job at analysis, and also you should refer to TEPCO's chronology of events, so that you can straighten your chronology out.

Posted by Laurie Sogawa on 08 Apr 2011


SORRY BUT I MUST TELL YOU AGAIN AND AGAIN...

NUCLEAR ENERGY IS NETHER CHEAP, NOR SAFE AND NEVER CLEAN.

SORRY, JUST IT IS NOT TRUTH!

BIG LIES, LIES, AND AGAIN CORPORATE LIES.

WHEN DO YOU WILL REMEMBER THIS?

Posted by NIJAZ DELEUT on 15 Dec 2011


Comments have been closed on this feature.
david bielloABOUT THE AUTHOR
David Biello has been covering energy and the environment for nearly a decade, the last four years as an associate editor at Scientific American. He also hosts 60-Second Earth, a Scientific American podcast covering environmental news. In previous articles for Yale Environment 360, Biello has written about geothermal technology and solar thermal technology and has explored the progress of carbon capture and storage technology.
MORE BY THIS AUTHOR

 
 

RELATED ARTICLES


As Small Hydropower Expands,
So Does Caution on Its Impacts

Small hydropower projects have the potential to bring electricity to millions of people now living off the grid. But experts warn that planners must carefully consider the cumulative effects of constructing too many small dams in a single watershed.
READ MORE

Why Wave Power Has Lagged
Far Behind as Energy Source

Researchers have long contended that power from ocean waves could make a major contribution as a renewable energy source. But a host of challenges, including the difficulty of designing a device to capture the energy of waves, have stymied efforts to generate electricity from the sea.
READ MORE

Life on Mekong Faces Threats
As Major Dams Begin to Rise

With a massive dam under construction in Laos and other dams on the way, the Mekong River is facing a wave of hydroelectric projects that could profoundly alter the river’s ecology and disrupt the food supplies of millions of people in Southeast Asia.
READ MORE

China’s Great Dam Boom:
A Major Assault on Its Rivers

China is engaged in a push to build hydroelectric dams on a scale unprecedented in human history. While being touted for producing lower-emission electricity, these massive dam projects are wreaking havoc on river systems across China and Southeast Asia.
READ MORE

Are Fast-Breeder Reactors
A Nuclear Power Panacea?

Proponents of this nuclear technology argue that it can eliminate large stockpiles of nuclear waste and generate huge amounts of low-carbon electricity. But as the battle over a major fast-breeder reactor in the UK intensifies, skeptics warn that fast-breeders are neither safe nor cost-effective.
READ MORE

 

MORE IN Analysis


Can Green Bonds Bankroll
A Clean Energy Revolution?

by marc gunther
To slow global warming, tens of trillions of dollars will need to be spent in the coming decades on renewable energy projects. Some banks and governments are issuing green bonds to fund this transformation, but major questions remain as to whether this financing tool will play a game-changing role.
READ MORE

What Is the Carbon Limit?
That Depends Who You Ask

by fred pearce
Scientists are offering widely varying estimates of how much carbon we can emit into the atmosphere without causing dangerous climate change. But establishing a so-called carbon budget is critical if we are to keep the planet a safe place to live in the coming century.
READ MORE

Beyond Treaties: A New Way of
Framing Global Climate Action

by fred pearce
As negotiators look to next year’s UN climate conference in Paris, there is increasing discussion of a new way forward that does not depend on sweeping international agreements. Some analysts are pointing to Plan B — recasting the climate issue as one of national self-interest rather than global treaties.
READ MORE

Oil Companies Quietly Prepare
For a Future of Carbon Pricing

by mark schapiro and jason scorse
The major oil companies in the U.S. have not had to pay a price for the contribution their products make to climate change. But internal accounting by the companies, along with a host of other signs, suggest that may soon change — though the implications of a price on carbon are far from clear.
READ MORE

Can Carbon Capture Technology
Be Part of the Climate Solution?

by david biello
Some scientists and analysts are touting carbon capture and storage as a necessary tool for avoiding catastrophic climate change. But critics of the technology regard it as simply another way of perpetuating a reliance on fossil fuels.
READ MORE

Mideast Water Wars: In Iraq,
A Battle for Control of Water

by fred pearce
Conflicts over water have long haunted the Middle East. Yet in the current fighting in Iraq, the major dams on the Tigris and Euphrates rivers are seen not just as strategic targets but as powerful weapons of war.
READ MORE

Peak Coal: Why the Industry’s
Dominance May Soon Be Over

by fred pearce
The coal industry has achieved stunning growth in the last decade, largely due to increased demand in China. But big changes in China’s economy and its policies are expected to put an end to coal’s big boom.
READ MORE

Obama’s New Emission Rules:
Will They Survive Challenges?

by michael b. gerrard
The sweeping nature of President Obama’s proposed regulations limiting carbon dioxide emissions from coal-fired power plants is likely to open his initiative to serious legal challenges. To date, however, the courts have given the federal government wide latitude in regulating CO2 under the Clean Air Act.
READ MORE

On the Road to Green Energy,
Germany Detours on Dirty Coal

by fred pearce
While Germany continues to expand solar and wind power, the government’s decision to phase out nuclear energy means it must now rely heavily on the dirtiest form of coal, lignite, to generate electricity. The result is that after two decades of progress, the country’s CO2 emissions are rising.
READ MORE

Why Wave Power Has Lagged
Far Behind as Energy Source

by dave levitan
Researchers have long contended that power from ocean waves could make a major contribution as a renewable energy source. But a host of challenges, including the difficulty of designing a device to capture the energy of waves, have stymied efforts to generate electricity from the sea.
READ MORE


e360 digest
Yale
Yale Environment 360 is
a publication of the
Yale School of Forestry
& Environmental Studies
.

SEARCH e360



Donate to Yale Environment 360
Yale Environment 360 Newsletter

CONNECT

Twitter: YaleE360
e360 on Facebook
Donate to e360
View mobile site
Bookmark
Share e360
Subscribe to our newsletter
Subscribe to our feed:
rss


ABOUT

About e360
Contact
Submission Guidelines
Reprints

E360 en Español

Universia partnership
Yale Environment 360 articles are now available in Spanish and Portuguese on Universia, the online educational network.
Visit the site.


DEPARTMENTS

Opinion
Reports
Analysis
Interviews
Forums
e360 Digest
Podcasts
Video Reports

TOPICS

Biodiversity
Business & Innovation
Climate
Energy
Forests
Oceans
Policy & Politics
Pollution & Health
Science & Technology
Sustainability
Urbanization
Water

REGIONS

Antarctica and the Arctic
Africa
Asia
Australia
Central & South America
Europe
Middle East
North America

e360 PHOTO GALLERY

“Peter
Photographer Peter Essick documents the swift changes wrought by global warming in Antarctica, Greenland, and other far-flung places.
View the gallery.

e360 MOBILE

Mobile
The latest
from Yale
Environment 360
is now available for mobile devices at e360.yale.edu/mobile.

e360 VIDEO

Warriors of Qiugang
The Warriors of Qiugang, a Yale Environment 360 video that chronicles the story of a Chinese village’s fight against a polluting chemical plant, was nominated for a 2011 Academy Award for Best Documentary (Short Subject). Watch the video.


header image
Top Image: aerial view of Iceland. © Google & TerraMetrics.

e360 VIDEO

Colorado River Video
In a Yale Environment 360 video, photographer Pete McBride documents how increasing water demands have transformed the Colorado River, the lifeblood of the arid Southwest. Watch the video.

OF INTEREST



Yale