Tokyo Electric Power Company, or TEPCO, has published information on the amount of radioactive material released after the accident, based on data and simulations taken from around the Fukushima Daiichi nuclear power plant.
A total of 900 quadrillion becquerels of iodine131 and cesium137 were leaked into the environment between March 12 and March 31, 2011. This is around 17 percent of what was released after the Chernobyl nuclear disaster. The level fell to more than one-1000th in April. While radiation levels around the plant continue to decrease, they still remain 7 years after the disaster.
The data released by TEPCO shows that the average amount of radiation released by the number 1 thorough 4 reactors every March amounted to 3.4 million becquerels per hour in 2012, 2.5 million becquerels per hour in 2013, 1.3 million becquerels per hour in 2014, and 1.2 million becquerels per hour in 2015. Following a review of the assessment methods, the figures stood at 270,000 becquerels per hour in 2016, 25,000 becquerels per hour in 2017, and 130,000 becquerels per hour in January 2018. While the number has increased this year compared to 2017, TEPCO says it is within the range of variation and maintains that the total level is continuing to drop.
The radiation level measured near the main entrance of the facility, located about 1 kilometer from the reactor building, was 1 microsievert per hour this month. The figure has hardly changed from a year ago.
Still, it's less than one-200th of the amount detected in the same location shortly after the accident, when levels reached a maximum of 236 microsieverts per hour.
Protective gear is no longer required in 95 percent of the plant's site.
The average number of TEPCO employees and subcontractors involved in decommissioning work stood at around 5,000 per day as of January 2018. That number has fluctuated between 5,000 and 5,500 since April 2017.
Decommissioning is underway
The latest roadmap established by the government and TEPCO in September 2017 says it could take 40 years at most to complete the decommissioning.
Removing spent fuel rods from the storage pools of the reactor buildings, as well as removing nuclear fuel debris, are the keys to carrying out the project.
Of the plant's 6 reactors, numbers 1 to 3 suffered meltdowns. Hydrogen explosions occurred in the buildings of number 1, 3, and 4.
The removal of nuclear fuel from the pool of the number 4 reactor was completed in 2014. The reactor avoided a meltdown as it was not operating and all its nuclear fuel had been moved to the pool at the time of the accident.
Decontamination and the removal of nuclear fuel debris are under way in the number 1 to 3 reactor buildings. They were severely contaminated by the meltdowns.
The fastest progress is reported in the number 3 reactor, with a dome-shaped cover and a construction crane, both necessary to remove nuclear fuel debris, having been installed in February.
TEPCO plans to begin removing fuel rods from the pool of the number 3 reactor around this fall after workers have gotten trained in remote-control and other operations. They also plan to do the same in the number 1 and 2 reactors in fiscal 2023.
Removing the nuclear fuel debris is expected to be the most difficult part of the decommissioning process. Chunks appearing to be fuel debris have been found inside the number 2 and 3 reactors in robot probes.
Pebble-like sediments appearing to be fuel debris were found on the bottom of the containment vessel of the number 2 reactor in January. A part of fuel assembly packaging was also found. Extremely high radiation of up to 8 sieverts an hour -- beyond a level permissible to human exposure -- was observed under the reactor core.
A robot was also deployed to check the number 3 reactor in July 2017. It showed dark rocky sediments on the bottom of the containment vessel that were not there before the accident. TEPCO said they are likely to be nuclear fuel debris.
No fuel debris was identified in a probe of the number 1 reactor in March 2017.
Dealing with the impact of extremely high radiation and the spread of radioactive substances will be a big challenge in fuel debris removal. One way that has been studied is filling the containment vessels with water. But the government and TEPCO say they will focus on a method known as "dry removal" -- extraction without filling the vessels with water.
The government and TEPCO plan to discuss details of fuel removal and decide by fiscal 2019 which reactor to start the process with, and begin actual removal in 2021.
The Industry Ministry says there have been delays in steps including fuel removal from the pools, but that hasn't led to any significant delays in the overall process. It says it will continue to carry out decommissioning safely and steadily without worrying too much about progress.
Tackling the issue of contaminated water
Water is being poured into the reactors 1 to 3 to help cool the molten nuclear fuel. It's becoming tainted with highly radioactive substances and is accumulating in the basement of the reactors.
With groundwater from the hillside of the plant also flowing into the buildings, tons of radioactive water has been building up.
TEPCO has been pumping up groundwater on the hillside of the plant before it reaches the reactors, and releasing it into the ocean. It calls the method a "groundwater bypass."
The utility has also introduced a "sub-drain" system, pumping up water using wells dug near the reactor buildings.
It is also keeping groundwater from reaching the site by freezing the soil around the buildings to surround them with a 1,500-meter-long wall of ice. TEPCO announced in November 2017 that the ice wall was nearly finished.
The utility announced in March that such measures have resulted in a decrease of 380 tons of contaminated water a day. It based the calculation on 3 months of data. It adds that the frozen wall alone helped to slash the amount by 95 tons a day.
A panel of government-appointed experts said the wall was effective to an extent, while more measures are needed to contain the increase of contaminated water, especially during heavy rains. The panel suggested that paving the ground around the buildings is needed to keep rainwater from entering them.
While systems have been installed to remove radioactive substances from the wastewater, they have not been able to remove radioactive tritium.
About one million tons of contaminated water is still being kept in nearly 850 tanks within the facility's premises. More than 75 percent of these tanks have tritium-tainted water.
Water containing radioactive tritium can be released into the sea after the concentration of the substance is reduced to below the government limit.
A chairman of the Nuclear Regulation Authority said releasing radioactive water would not affect the environment and ecological systems, and that it is up to TEPCO to decide on how to proceed.
But local fisheries are concerned that discharging radioactive water into the sea could spark harmful rumors and affect their businesses. TEPCO remains undecided over how to deal with the contaminated water.
74% drop in radiation levels within 80km of Fukushima Daiichi plant
The Nuclear Regulation Authority, or NRA, uses helicopters to gauge per-hour radiation levels one meter from the ground in areas within 80 kilometers of the plant. It creates maps that show differences in radiation levels using 9 colors.
A map created using a similar method 7 months after the nuclear accident shows yellow and red areas stretching more than 30 kilometers northwest of the plant. The colors mean more than 3.8 microsieverts per hour of radiation were observed there. That comes out to an over 20 millisieverts annually, which is the threshold for issuing evacuation orders.
The latest survey held last September shows areas with over 3.8 microsieverts per hour had shrunk outside the 30-kilometer radius of the plant. The level was still recorded in parts of Iitate Village and Namie Town.
The NRA says the comparison of the 2 sets of data shows radiation levels fell about 74 percent on average within areas 80 kilometers of the plant.
It explains that 63 percent accounts for radioactive substances turned into non-radioactive material. It adds that the remaining 11 percent was due to other factors.
Since 2016, the NRA has been gauging radiation levels in 5 municipalities using vehicles on the request of Okuma Town, Futaba Town and other municipalities that have areas subjected to evacuation orders.
It has been releasing the results of the survey in the form of maps with greater details than those created in aerial surveys. It hopes the data will be used in discussions on whether to allow evacuees to return home.
Prospects for nuclear reactors in Japan
Japan has 40 reactors at 16 plants, excluding the reactors set to be decommissioned.
Operations of 6 nuclear reactors at 4 plants were resumed under new regulations adopted after the 2011 nuclear accident at the Fukushima Daiichi power plant. Three more reactors at 2 plants are likely to be restarted between March and May.
The Nuclear Regulation Authority holds safety screenings under the new regulations, a precondition to restart reactors. It has so far received screening applications for 26 reactors. They include reactors at the Oma plant, which is under construction in Aomori Prefecture.
Twelve pressurized water reactors at 6 plants passed the screening. Of them, operations were resumed at the number 1 and 2 reactors at the Sendai plant in Kagoshima Prefecture, the number 3 reactor at the Ikata plant in Ehime Prefecture, and the number 3 and 4 reactors at the Takahama plant in Fukui Prefecture.
The operation of Ikata's number 3 reactor has been suspended due to an injunction ordered by the Hiroshima High Court last December. Operation of Sendai's number 1 reactor has also been suspended for regular inspections. This means 3 reactors at 2 plants are currently online in the country.
The number 3 reactors at the Ohi plant in Fukui Prefecture and the Genkai plant in Saga Prefecture are expected to be put back online this month. The number 4 reactors at both plants are also likely to be restarted in May.
The NRA received screening applications for 10 boiling water reactors at 8 plants. They're the same type as the crippled Fukushima Daiichi reactors.
The number 6 and 7 reactors at the Kashiwazaki-Kariwa plant in Niigata Prefecture cleared the screening last December, becoming the first boiling water reactors to do so under the new regulations.
The screening for the sole reactor at the Tokai Number 2 plant in Ibaraki Prefecture is in the final stages. Whether the life span of the reactor will be extended will be another focus as the facility will reach its operational limit of 40 years in November.
Meanwhile, 8 reactors at 6 plants, excluding the Fukushima Daiichi, will be decommissioned largely due to huge costs of safety measures.
Kansai Electric Power Company, the operator of the Ohi plant, decided last December that it will scrap the plant's number 1 and 2 reactors. The utility cites massive costs of measures to prevent serious incidents.
The generation capacity of the reactors is relatively large at more than one million kilowatts each. Estimates show that if the reactors were put back online, they would improve the firm's financial conditions by 9 billion yen, or about 84 million dollars, per month.