Fukushima Nuclear Accident

After a magnitude 9 earthquake on March 11, 2011, a 40-foot tsunami swept over the seawall at the Fukushima Daiichi nuclear power plant, cutting off electricity for control panels and cooling pumps. A series of crises followed over several days, resulting in three core meltdowns and a half-Chernobyl release of radiation. Cleanup at the site continues to be plagued by unforeseen complications.

Fukushima's reactors shut down properly after the earthquake, but the tsunami swamped the plant's emergency generators. The resulting situation, which included a prolonged loss of primary and backup power, was not anticipated by plant designers or in emergency plans. With cooling systems down, nuclear materials heated up in four reactor buildings. Overlapping events forced ad hoc solutions, and poor communications among decision-makers made matters worse. At the height of the emergency, explosions sent plumes of radioactive gas into the air. Residents within a 12.5-mile radius were evacuated. No deaths or cases of illness were definitely linked to the Fukushima accident. Two years later, Tokyo Electric Power Company (TEPCO) was still encountering new challenges at the site that required elaborate, one-time solutions, such as a mile-long ice wall to stop the runoff of contaminated groundwater.

Note: References to "Fukushima" are to the Fukushima Daiichi facility. Another power plant, Fukushima Daini, is located 7 miles to the south. The four reactors at Fukushima Daini shut down after the earthquake without problems.

Date: The earthquake began on Friday, March 11, 2011, at 2:46 Japan Standard Time. The tsunami hit the coast about an hour later.

Place: The Fukushima Daiichi nuclear power plant is about 150 miles north of Tokyo.

Key Events

• 1970 -- Construction completed on Fukushima Reactor #1. By 1979, the plant has six reactors.
• April 2003 -- A weak safety culture at Tokyo Electric Power Co (TEPCO) is revealed when the company admits to falsifying inspection records. All 17 TEPCO reactors are temporarily shut down.
• March 2011 -- Tsunami starts a cascade of events that run ahead of efforts to maintain control of the power plant.
• August 2013 -- Flow of contaminated groundwater into the ocean is estimated at 400 tons per day.
• November 2013 -- TEPCO begins removing fuel assemblies from Reactor 4. The delicate work of extracting 1,500 assemblies is expected to take until the end of 2014.
• 2040s -- Fukushima decommissioning is completed as the last fuel assemblies are put in safe storage.

Status

The situation at Fukushima is not completely stable or fully under control. Removal of fuel rods from Reactor 4 is complicated by building damage and debris. If an earthquake or accident were to drain off cooling water, the exposure of 400 tons of nuclear fuel to air could result in a catastrophic release of radiation. International observers question TEPCO's capability.

Assorted problems with contaminated water hampered cleanup efforts in late 2013. Six workers were doused in October when a pipe was disconnected by mistake. In the same month, rainfall caused 12 of 23 containment areas to overflow. The spillover in some places was contaminated at 71 times the safety standard. Walled containment areas surround Fukushima's 1,000 storage tanks for contaminated water. The tanks were constructed in a rush after the March 2011 accident and have begun to leak.

In-Depth Description

The March 2011 earthquake and tsunami had disastrous effects throughout Japan, killing nearly 20,000 people and destroying or damaging half a million buildings. Within the Fukushima nuclear power plant, there was no significant damage to buildings from the earthquake. However, electricity was cut off due to downed power lines, and then the tsunami flooded the backup generators, all but one of which were housed underground. The facility switched to battery power, which ran out the following day. On Saturday, March 12, Fukushima was without power for control panels and cooling pumps.

Of the six reactors on site, numbers 5 and 6 were already in full shutdown at the time of the earthquake. Reactor 4 had been de-fueled in preparation for maintenance. Reactors 1, 2, and 3 had nuclear fuel in their cores. Over the next few days, all three experienced core meltdowns. In addition, in Reactors 1 through 4, the cooling pools for spent fuel lost some of their water due to the intense heat. Partial exposure of the spent fuel further increased heat and radioactivity levels. There were explosions of hydrogen gas in Reactors 1 and 3. Damage to the roofs of Reactors 1, 3, and 4 allowed the release of highly radioactive plumes across northeast Japan and the Pacific Ocean.

Interlocking Crises

In retrospect, the Fukushima nuclear accident can be understood as a series of crises that: 1) began with the failure to plan for a prolonged loss of power, 2) multiplied because of the near proximity of reactors to one another, and 3) escalated when corrective actions were delayed by failures in knowledge and communication.

The cascade of events started in Reactor 1 on the first day, when fission had been halted in the core. The cooling system was working normally but on battery power. An operator mistakenly deactivated a valve that seemed to be malfunctioning, and this caused core temperatures to rise faster than expected. Supervisors failed to ascertain conditions in the core when they vented it the following day, March 12. Venting the core released hydrogen gas, which formed as a result of the high core temperature and chemical reactions between cooling water and fuel cladding. The hydrogen exploded, blowing the roof off the building and releasing a cloud of radioactive material. The crisis in Reactor 1 drew resources away from Reactor 3, where a similar explosion and roof damage occurred on March 14. This explosion also damaged pipes delivering seawater to Reactor 2. The core in Reactor 2 then melted and sank to the bottom of the core vessel. A second explosion in Reactor 3, on March 15, may have caused the roof damage in Reactor 4 that opened yet another path for escaping radiation. In Reactors 1 through 4, heat increased as water levels went down in cooling pools for spent fuel. Spent fuel, when exposed to air, became a potent source of additional radiation.

Power lines to Fukushima were repaired on March 17, and plant managers eventually regained control of the facility, using normally available resources. During the period when power was out, decision makers faced a convergence of crises without an adequate emergency plan. They improvised solutions, which included dousing the reactors with water from helicopters, fire trucks, and cement trucks. Issues of authority and shared decision making came into play as the government lost confidence in the plant operator, the Tokyo Electric Power Company (TEPCO). There were communication problems within TEPCO, as top executives were delayed for days in reaching Fukushima. Similar problems arose on the government side, as Prime Minister Naoto Kan saw that officials of the Nuclear and Industrial Safety Agency (NISA) were not able to give useful technical guidance. Critics of NISA said the agency functioned as an industry promoter rather than a watchdog.

Contamination and Effects

Radioactivity streaming into the air from Fukushima after the explosions has been estimated at 40 to 50 quadrillion becquerels -- roughly half the level at Chornobyl. Though the plume crossed over northeastern Japan, it appears that people on the ground were not exposed to radiation levels that would cause near-term harm. Dosimeter readings two weeks after the accident showed varying rates of absorbed radiation, with the highest at 78 microsieverts per hour. This is a high exposure rate but would take weeks to reach the limit of 100 millisieverts, where the risk of cancer begins to increase.

Radioactivity continues to escape from the damaged buildings at Fukushima. Emissions declined soon after the first massive releases and have stayed around 10 million becquerels since February 2012. A 2013 study by the World Health Organization predicted small increases in cancer risk for those who lived close to the plant at the time of the accident. People exposed as infants faced the highest risks, with leukemia expected to increase by 6 to 7 percent and cancers involving tumors by 4 percent. Thyroid cancer, which has a low rate of occurrence and is more common in women than men, was likely to increase 70 percent among females who were exposed as infants. In ocean water off Fukushima, radioactive contamination is low enough to meet drinking water standards. However, 10 percent of the fish caught in these waters have levels of cesium 137 too high for eating. Scientists have discovered hotspots of radiation in the nearby ocean floor, thought to be depressions where radioactive material has accumulated.

Among workers at the Fukushima plant, levels of absorbed radiation climbed during two years of site cleanup. By July 2013, there were 138 workers at the maximum permitted exposure. Another 331 were in the range of 75 to 100 millisieverts and would not be allowed to work at Fukushima much longer. Morale has been low, and there are questions about finding enough replacement workers with the necessary training.

Holding Back Contaminated Water

In August 2013, TEPCO acknowledged that groundwater flowing under the Fukushima plant had recently begun to show increased levels of contamination. Officials said the increase was likely coming from reactor basements. In addition, some of the 1,000 cement storage tanks for contaminated cooling water, which had to be built in a hurry after the accident, had begun to leak. To hold back the flow of contaminated groundwater, estimated at 400 tons per day, TEPCO announced plans to build a mile-long ice wall.

The ice-wall strategy is a proven technique in mining and has been used at toxic cleanup sites. A nuclear facility in Oak Ridge, Tennessee, maintained a 300-foot ice wall from 1998 to 2004. The plan at Fukushima called for drilling pipes through the underlying clay to a depth of 100 feet. Coolant circulated through the pipes would freeze water in the soil to form the ice wall. If the wall is fractured for any reason, surrounding water would flow into open spaces and freeze, resealing the wall. Once the soil was frozen, keeping it frozen would be easy and cheap. The ice wall at Oak Ridge was maintained for about $15 per day.

Decommissioning the Reactors

In November 2013, TEPCO began removing the 1,500 fuel assemblies stored in Reactor 4. The work had high priority because of possible deterioration of the spent fuel cooling pool, which had been filled for a time with seawater as an emergency measure. If a new earthquake were to crack and drain the pool, exposure of all 1,500 fuel assemblies would cause a catastrophic release of radiation, potentially requiring evacuation of Tokyo. The cooling pool,a 30-by-36-foot concrete structure containing water 21 feet deep, is located on the fourth story, more than 50 feet up.

Removal of fuel, ordinarily a routine task, was complicated in Reactor 4 by structural damage and debris. The fuel assemblies, each weighing about 660 pounds, had to be lifted one at a time by crane and transferred to a 90-ton cask, which was then moved to another building, about 100 yards away, for long-term storage. Crews of six worked only two hours at a stretch to minimize their exposure to radiation. The decommissioning of Reactor 4 is scheduled to be completed by the end of 2014.

Because of core meltdowns, Reactors 1, 2, and 3 are still too hot to allow removal of their nuclear fuel. TEPCO used robots to explore inside these reactor buildings. However, they were unable to determine the exact positions and conditions of nuclear fuel. Complete decommissioning of all Fukushima reactors is expected to take three or four decades.

In 2023, Japan caused great controversy with an announcement that it intended to begin releasing over one million metric tons of treated, radioactive water from the Fukushima reactors back into the Pacific Ocean. This action brought about immediate protests from countries such as China which halted imports of Japanese seafood. The Japanese plan was also caused consternation in South Korea where thousands of citizens joined in a protest. According to media reports, demand for Korean seafood has dampened because of the Fukushima accident. For many, the incident harkened memories of Japanese aggression during World War II, and the release of the Fukushima waters had very negative impacts on the goodwill felt toward Japan. On August 30, 2023, Japanese Prime Minister Fumio Kishida and three cabinet ministers sought to assuage public concerns and backlash by publicly eating fish reported to originate in the waters around Fukushima.

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(August 30, 2023). Japanese ministers eat Fukushima fish to show it’s safe after nuclear wastewater is discharged into ocean. Associated Press. https://www.pbs.org/newshour/world/japanese-ministers-eat-fukushima-fish-to-show-its-safe-after-nuclear-wastewater-is-discharged-into-ocean#.

(August 24, 2023). Japan’s neighbors share fear and frustration over radioactive water release. PBS NewsHour.https://www.pbs.org/newshour/world/japans-neighbors-share-fear-and-frustration-over-radioactive-water-release.

Murakami, Sakura and Tom Bateman. (August 23, 2023). Japan to release Fukushima water into ocean from Aug. 24. Reuters. https://www.reuters.com/world/asia-pacific/japan-release-fukushima-water-into-ocean-starting-aug-24-2023-08-22/.

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