What exactly happened at Fukushima? And how can we prevent an event like that from happening again? Those are the most important questions facing the public and the future of nuclear power after the Great Tohoku Earthquake and tsunami.
They are also very difficult to answer. Let’s begin by looking at the Fukushima meltdowns day by day.
On the Scene of a Disaster
March 11, 2011: On the day of the earthquake, Fukushima Daiichi reactor 1 is one of the oldest nuclear reactors in Japan. It has been in operation since 1971. It probably should be replaced, but TEPCO wants to get as much use out of it as possible.
At 2:46 p.m., the shaking starts. Strong earthquakes are common in Japan, so the plant has been built to withstand a jolt at least as large as 8.5 on the Richter scale. But this earthquake measures 9.0.
When the earthquake alarm sounds, reactor 1 workers head for the exits. On the way out, a twenty-seven-year-old maintenance engineer senses trouble. “I personally saw pipes that came apart,” he tells a reporter later. “There’s no doubt that the earthquake did a lot of damage inside the plant.”
A technician in his late thirties recognizes the first signs of a meltdown. “I could see that several pipes had cracked open, including what I believe were cold water supply pipes,” he recalls in an interview. “That would mean that coolant couldn’t get to the reactor core.”
Though TEPCO doesn’t know it yet, the technician is right. Reactor 1 is in deep trouble. It is losing cooling water. Its core will soon begin melting down, and no one will be able to do anything to save it.
Meanwhile, in reactor 2, the first shaking makes Hiroyuki Kohno pause. He’s not even sure it is an earthquake. It could be a minor turbine problem. Then the building shudders and warning sirens blare. He and his fellow workers hurry out as parts of the ceiling crash around them. The core of the nearly thirty-six-year-old reactor is not damaged.
Outside, Kohno’s coworkers are “shouting about a tsunami. At that point, I really thought I might die,” he recalls. Instead of going to their cars, the workers are heading for the safety of upper floors of buildings or higher ground.
The tsunami in Japan washed away a warehouse and vehicles in a coastal town in Miyagi Prefecture, leaving a road covered with a mountain of debris. It took workers nearly three months to clear the road.
From the top of a small hill, Kohno sees black smoke coming from the reactors. That’s a good sign. It is the exhaust of the large backup diesel generators that pump cooling water when the outside electricity fails. As long as that water flows, there will not be a meltdown.
The early indications are also good in the power plant operations
center. In the first minute of the quake, the control rods drop into all the reactor cores. That stops the chain reactions. At 3:27 p.m., the first wave of the tsunami slams into the 10 m (33 ft) seawall. At a little higher than 4 m (13 ft), it causes no problem.
But behind it is a monster. At 3:35 p.m., a 15 m (50 ft) wave rolls over the barrier. It tosses cars around like bathtub toys and heads for the reactors. It knocks out the backup generators and washes away their fuel tanks.
By 3:52 p.m., the workers in the control room fear the worst for reactor 2. Their whiteboard is filled with notes about the growing crisis. They add “ECCS injection not possible” to the list. That means water is not flowing from its Emergency Core Cooling System. To keep the core from melting down, TEPCO workers hurry to find a way to replace water as it boils off. They start spraying the core with high-pressure hoses to keep it cool.
As TEPCO workers desperately tried to avoid a meltdown at the Fukushima plant, members of Japan’s self-defense force evacuated people (above) from towns devastated by the tsunami.
March 12, 2011: Things are only slightly better for reactor 3. Its emergency batteries keep the cooling-water pumps operating until their power runs out. Early on the morning after the quake, those batteries die. The flow of cooling water stops, and evaporation begins. Ninety minutes later, the fuel rods are no longer completely under water. Workers are now spraying two cores at once, desperately trying to prevent meltdowns.
TEPCO still doesn’t know how serious the leaks are at reactor 1. In fact, its core has already almost completely melted. The hot zirconium alloy is beginning to react with water to produce hydrogen. But unlike at TMI, the hydrogen is mixing with air. At 3:36 p.m., one day and fifty minutes after the earthquake, a powerful explosion brings down the concrete building around reactor 1.
Radioactivity is escaping into the air. To stop more from getting into the environment, TEPCO brings in fire trucks to pump seawater onto reactor 1’s core.
March 13–15, 2011: Early on March 13, the high-pressure spray system for reactor 3 stops working. By 9:00 a.m., its core begins to melt. On the morning of March 14, its building explodes. By 3:00 p.m., most of its fuel has melted to the bottom of the reactor vessel.
The March 14 explosion at reactor 3 damages the water supply for reactor 2. By 1:15 p.m. that day, that spray stops completely. At 8:00 p.m., the reactor begins melting down. A day later, its meltdown is also complete.
But that is not the end of the trouble at Fukushima Daiichi.
This diagram shows a boiling water reactor like the three that melted down at Fukushima Daiichi. One loop of water is pumped through the reactor core where it absorbs the heat from a controlled nuclear chain reaction and boils. Under high pressure, the steam gets very hot. It enters a pipe that carries it to a heat exchanger. The outside of that pipe becomes hot enough to boil water in a second loop. That creates steam to drive an electric generator. The meltdowns occurred when the pumps lost power and the heat in the reactor core could not be transferred away.
Trouble from Spent Fuel Rods
One of the problems of nuclear power is what to do with the spent fuel rods—rods that are no longer useful. They haven’t used up all their U-235, but they have enough fission products to spoil the chain reaction. They also contain plutonium.
Most reactors store spent fuel in water-filled pools. The rods stay under water for many years until the radioactivity from the fission products has died down. Heat from that radioactivity makes water evaporate from those pools, so it has to be replaced constantly. If the spent fuel pool goes dry, the rods can catch fire.
Fukushima Daiichi has six spent fuel pools, one for each reactor. While TEPCO workers are busy fighting three meltdowns, they also have to worry about water for spent fuel pools at all six reactors. The pools for reactors 3 and 4 are the most troublesome. They may be leaking. Military helicopters dump giant buckets of seawater onto these storage pools to keep them from going dry.
Firefighters gather to douse overheated reactors with water at the Fukushima Daiichi nuclear power plant on March 18, 2011, one week after the earthquake and tsunami hit Japan.
Evacuation and Rolling Blackout
Meanwhile, the Japanese government declares an evacuation zone. They urge everyone living within 20 km (12 mi) of Fukushima Daiichi to leave as soon as possible. Government workers have detected radiation levels in that area that put people’s health in serious jeopardy.
Tap water in the area is too radioactive for infants to drink. Farmers have to destroy vegetables and milk contaminated with radioactivity. Seafood in coastal waters is also contaminated from the overflow of radioactive water from storage tanks.
Besides people in the area that immediately surrounds the reactors, the rest of Japan faces electric
power shortages right after the earthquake and tsunami. Other Japanese nuclear plants shut down as a precaution.
People and businesses lose power periodically as TEPCO and other companies schedule rolling electrical blackouts to share the burden the best way they can. Many manufacturers have to shut down. All over the world, automobile companies and dealers face shortages of important parts.
In late April, the Japanese government makes it illegal to stay in the evacuation zone. It takes weeks before normal electric service is restored.
Step by step, TEPCO begins bringing the situation at Fukushima under control. But it is a long process to reach “cold shutdown,” where the core is cool enough that the meltdown will not begin again.
By midsummer 2011, officials can see that cold shutdown is still at least six months in the future. Only then will officials determine which areas are safe enough for evacuees to return. They will measure the dangerous radioactive isotopes in the soil and water. Some places will only be safe after the top layer of soil has been carted away. Others might not be safe for years.
Officials wear protective gear to scan evacuated people in Koriyama, Japan, for radiation levels. This city is about thirty minutes from the Fukushima power plant.
Comparing Fukushima to TMI and Chernobyl
Almost as soon as the news comes of the Fukushima meltdowns, official investigations begin. They all ask the same question: was Fukushima more like TMI or Chernobyl?
To answer that, scientists will study the meltdowns and the spread of radioactivity at Fukushima Daiichi for years to come. But we already know enough about the disaster to say that it is much worse than TMI and not as bad as Chernobyl.
TMI had only a single meltdown and only a minor release of radioactivity. Fukushima had three meltdowns plus problems in the spent fuel storage pools. It had two large explosions and several fires.
TMI had no measurable health effects, not even among the power plant workers. It led to only a short evacuation of pregnant women and children over a small distance. Fukushima has forced tens of thousands of people out of their homes for months. It has exposed them to a small amount of extra radiation.
The workers bringing the Fukushima Daiichi to cold shutdown will face some health concerns later in life. A few have had mishaps that exposed them to serious levels of radioactivity. The rest have been adding to their total radiation dose with every hour of work. That gives them a higher than average cancer risk though not a certainty of the disease.
The total health impact of Fukushima’s radiation is much less than Chernobyl’s. The Chernobyl meltdown began with a raging, smoky fire that turned an entire reactor core into dust. The firefighters who battled it faced deadly levels of radiation.
Smoke from Chernobyl’s burning graphite core released seven times as much radiation as the Fukushima meltdowns. Contamination from Chernobyl spread far from the power plant. The radiation from Fukushima caused very little threat beyond the evacuation zone.
Still, Fukushima’s impact on human lives is huge. How do you measure what it means to be forced out of your home or off your farmland?
Beyond the damage and human costs, Fukushima also raises serious questions about nuclear power plants in the future. Will nuclear power bounce back just as it did after TMI and Chernobyl? Or has the industry suffered a meltdown from which it will never recover?
A woman in Ishinomaki, Japan, stares in shock at the damage caused by the tsunami. The emotional toll among people impacted by the natural and nuclear disasters includes sleeplessness, anxiety, and depression.