Much has transpired during the nearly six months following the Great East Japan Earthquake—a 3-minute, magnitude 9.0 temblor that generated a series of tsunami waves as tall as 38.9 meters (130 feet), killed more than 25,000 people, and set off the worst nuclear disaster in 25 years.
Major achievements have been accomplished, including stabilization of the reactors at Fukushima Daiichi (where most units have experienced substantial core meltdown), assembly of a cover, and restoring recirculating cooling to used-fuel storage pools. But embattled plant owner Tokyo Electric Power Co. (TEPCO) still has much to do to quell the crisis, while power shortage-stricken Japan is considering an energy future overhaul.
Meanwhile, the accident has left its mark on the global nuclear landscape.
The Quake That Rattled the Industry
At 2:46 p.m. on Friday, March 11, 11 reactors at four nuclear power plants on the eastern coast of Honshu Island were operating when the rare and complex temblor rattled the region. The plants online in the affected area at the time were TEPCO’s Fukushima Daiichi Units 1, 2, and 3; TEPCO’s Daini 1, 2, 3, and 4; Tohoku Electric Power Co.’s Onagawa 1, 2, and 3; and Japan Atomic Power Co.’s Tokai—a total of 9,377 MW.
While the quake caused a brief fire at Onagawa 1, a 15-meter (49-foot) tsunami inundated and disabled the offsite power supply (12 of 13 backup generators located in the basements of the turbine buildings) of the three units at Daiichi, interrupting critical cooling functions. The tsunami also disabled their heat exchangers and electrical switchgear. All three units consequently saw explosions that damaged their reactor buildings. It was also later established that the cores of Daiichi 1, 2, and 3 had largely melted within the first three days of the crisis.
A comprehensive report dated June 8 from Japan’s Nuclear and Industrial Safety Agency (NISA) submitted to the International Atomic Energy Agency (IAEA) Ministerial Conference on Nuclear Safety concluded that a reaction between the zirconium of the fuel-cladding tubes and water vapor generated a large amount of hydrogen, and the gas and radioactive materials discharged into the primary containment vessel (PCV) when TEPCO depressurized the reactor pressure vessels (through wet well venting). The gas containing the hydrogen leaked and accumulated in the upper area of the reactor buildings and triggered the explosions at Units 1, 2, and 3.
At Unit 4, where the reactor had been shut down for periodic inspection, the nuclear fuel had been transferred to a spent fuel pool. But after the tsunami, both cooling and feedwater functions were lost, forcing crews to spray water over the pool. On March 15, the reactor building of that unit also exploded, blowing out the walls above the bottom of the operation floor. Later, a fire broke out near the fourth floor of the reactor building. "With regard to the explosion in the reactor building, one may doubt the possibility of inflow of hydrogen from unit 3 as the exhaust pipe for venting the PCV joins the exhaust pipe from unit 4 before the exhaust stack," NISA says. "However, the cause of [the explosion] has not yet been identified."
Three TEPCO employees at the plant were killed directly by the earthquake and tsunami. On April 11, a month after the crisis began, NISA provisionally rated the accident a level 7 on the International Nuclear and Radiological Event Scale , giving it a similar magnitude to the Chernobyl disaster of April 1986. All four reactors were subsequently written off.
Identifying a Path Forward
On April 20, TEPCO released its so-called "Roadmap towards Restoration," a plan of action to ensure that radiation doses are in steady decline. The first step, expected to take three months, entailed trying to prevent additional hydrogen explosions inside the reactor PCVs through injection of nitrogen to keep the concentration of hydrogen and oxygen below flammability limits. The second step, spanning three to six months, entails ensuring that the release of radioactive materials is under control. The third step foresees TEPCO maintaining and protecting the reactors in cold shutdown within three years.
In a major milestone on July 20, the company successfully achieved consistent and stable cooling of the reactors, completing Step 1. In August, in another groundbreaking update to its roadmap, it said the amount of radioactive substances leaking from Units 1, 2, and 3 dropped to a maximum 200 million becquerels per hour, from 1 billion becquerels per hour a month earlier. The company stopped short of saying it had achieved cold shutdown because the roadmap defines that term as bringing the temperature at the bottom of the pressure vessel—where the reactor cores are believed to have melted—to below 100C while largely reducing and controlling the leakage of radioactive materials. As part of Step 2, the company is now also working with the government to decontaminate a 20-kilometer radius around the plant.
One problem TEPCO encountered is that while cooling Daiichi 2 with freshwater injection, highly contaminated water in the turbine building would increase, which increased the possibility that the water could leak outside the contained area. In late June, the company installed a water filtration system to decontaminate and recycle radioactive water that had flooded the basements. The system is not perfect—it has operated at only 53% of capacity—and has been halted several times. The company is also struggling to identify and plug containment vessel leaks of contaminated water. TEPCO recently said it would install a second treatment system and use it alongside the existing one.
Meanwhile, in late August, workers achieved another major milestone of restoring recirculating cooling (rather than water injection) to used-fuel storage pools at the last of the four damaged reactors. Workers activated the cooling system at Unit 1’s pool on Aug. 12. Cooling systems for the pools were restored at reactor 2 on May 31; reactor 3, June 30; and reactor 4, July 31. The cooling systems for the pools at reactors 5 and 6 and the common pool were not damaged.
Work is also reportedly under way to begin desalinating water (from injected seawater for emergency cooling) in the fuel pools, starting with Unit 4, to reduce salt-induced corrosion of pipe walls and pool walls.
Efforts are also ongoing on the construction of a cover that will be installed over Unit 1, which was damaged by a hydrogen explosion on March 12. The cover, a temporary measure to protect the reactor from rain and to prevent radiation release, is expected to be completed in September, though the plans include a contingency margin to the end of November.
The IAEA on March 19 reported that radiation levels in the air around Daiichi had surged three times after the earthquake—particularly near Unit 3, where it peaked at 400 millisieverts/hr (mSv/hr)—but had stabilized since March 16 at a range that allowed workers to continue onsite recovery measures. TEPCO has since been spraying a dust-suppressing polymer resin around the plant to prevent fallout from being spread by wind or rain, covering about 40 hectares (99 acres) by mid-July. Considerable work to contain radioactive debris onsite also continues.
Japan news agency Kyodo News on Aug. 26 reported that the country will designate 220 billion yen ($2.87 billion) to clean up contaminated areas, hoping to reduce radiation exposure levels to less than 1 mSv/year. The central government will decontaminate areas where radiation exceeds 20 mSv/year a year, while local authorities will clear less-toxic areas, it said.
A Toll on TEPCO
In early August, despite passage of a law in Japan’s parliament that will allow use of public funds to help TEPCO pay more than $26 billion in compensation claims, TEPCO reported it had booked a net loss of 571.76 billion yen ($7.38 billion) for the April-June quarter after incurring massive costs to deal with the ongoing nuclear crisis. Japanese media reported the central government voted to back the measure to enable quick compensation payments to victims of the accident and jump-start economic growth in the disaster zone. One consideration was that the size of the payments without government support could render the plant operator insolvent.
TEPCO’s massive loss compares to a 5.45 billion yen loss in the same period last year, and it is a major reversal from an operating profit of 62.88 billion yen in 2009. In May, TEPCO reported a net loss of 1.25 trillion yen for the last fiscal year, which ended in March.
Japan’s Nuclear Sector in Limbo
In late August, Japan’s Prime Minister Naoto Kan, who has been criticized for failing to show leadership after the earthquake and Fukushima nuclear disaster, stepped down as head of the ruling Democratic Party of Japan.
Public confidence in Japan’s government dealings with nuclear power has also been ailing, and in August, the government unveiled plans to reform the country’s nuclear regulatory agency into a safety-oriented agency, rather than one that fosters the traditional model of government-industry relations. But the change means the new agency will not be an independent agency; instead, it will be placed under the jurisdiction of the Environment Ministry.
Meanwhile, some parliamentary leaders have sharply different opinions about whether the country will shut down all 54 of its reactors by May 2012, if safety fears delay their restart after regular maintenance. Proponents of nuclear power warn that shutting down all reactors would sharply increase pollution, greenhouse gases, and power costs for the recovering economy.
In July, the government estimated that if Japan had to operate without any reactors, it would only be able to supply 162,970 MW of power next summer, which would mean a potential 9.2% shortfall. Meanwhile, the Institute of Energy Economics for Japan (IEEJ) estimated that Japan’s power supply without any nuclear reactors would fall 7.8% short of an anticipated 182,000 MW peak demand next summer. The energy group forecasts the shortage even with the assumption that utilities will increase run rates for existing coal-, oil-, and gas-fired plants to 85%, almost 100%, and 70% respectively. The IEEJ also estimates utilities would have to spend 3.6 trillion yen ($46 billion) more on fuel imports in the fiscal year ending March 2013 compared with 2010/11, potentially boosting electricity bills by 3.9 yen per kilowatt-hour.
Only 16 nuclear reactors are currently operating in the country after the earthquake. They produced about 18% of the country’s power supply in June (compared with about 30% before March 11).
The International Fallout
According to the London-based World Nuclear Association (WNA), governments all over the world issued a range of political decisions in response to the Fukushima Daiichi accident. "Some established nuclear countries such as the USA and France have largely come out in support of their existing fleet and industry, while other countries, notably Germany, have affected a dramatic about face on nuclear policy amid renewed concerns about reactor safety," it said. "Many countries that have been considering introducing nuclear power for the first time have now delayed plans at least until safety lessons from the event can be learned."
The organization notes that many safety authorities have embarked upon reviews to see what lessons can be learned from the accident. "Countries with operating reactors are intent on setting up programs, so called ‘stress tests’, to see how their fleet would perform in the face of a disaster that results in reactor shutdown and a prolonged loss of grid and emergency power – such as happened at Fukushima Daiichi," it said. "In Japan, detailed reports into the accident and emergency response are in the process of being put together by specially appointed task forces. There is also an international investigation underway, with the sharing of information and expertise between countries co-ordinated through [the IAEA]."
—Sonal Patel is POWER’s senior writer.