Fukushima disaster cleanup
The multiple nuclear reactor units involved in the Fukushima Daiichi nuclear disaster were close to one another and this proximity triggered the parallel, chain-reaction accidents that led to hydrogen explosions blowing the roofs off reactor buildings and water draining from open-air spent fuel pools. This situation was potentially more dangerous than the loss of reactor cooling itself. Because of the proximity of the reactors, plant workers were put in the position of trying to cope simultaneously with core meltdowns at three reactors and exposed fuel pools at three units.
Automated cooling systems were installed within 3 months. A fabric cover was built to protect the buildings from storms and heavy rainfall. New detectors were installed at the plant to track emissions of xenon gas. Filters were installed to reduce contaminants from escaping the area of the plant into the area or atmosphere. Cement has been laid near to the seabed to control contaminants from accidentally entering the ocean. The biggest costs for the cleanup will be the final decommissioning of the reactors, a process estimated to take 10–30 years.
Cleanup costs will not be fully known until the cleanup is completed and the decommissioning is complete. No strontium was released into the area from the accident; however, in September 2013 it was reported that the level of strontium-90 detected in a drainage ditch located near a water storage tank from which around 300 tons of highly toxic water was found to have leaked was believed to have exceeded the threshold set by the government.
Decommissioning the plant is evaluated to cost tens of billions of dollars and last 30–40 years. Initial fears that contamination of the soil was deep have been reduced with the knowledge that current crops are safe for human consumption and the contamination of the soil was not serious; however, in July and August 2013, it was discovered that radioactive groundwater has been leaking into the sea.
- 1 Overview
- 2 Scope of cleanup
- 3 Working conditions at the plant
- 4 Preventing hydrogen explosions
- 5 Investigations inside the reactors
- 6 Water treatment
- 6.1 TEPCO warned after recurrent leakage of radioactive strontium-contaminated water
- 6.2 Water in the basement
- 6.3 Pumping the water from the basement
- 6.4 Influx of groundwater
- 6.5 Building a frozen wall, enlarging the storage for contaminated water
- 6.6 Slightly radioactive water found under the waste water treatment facility
- 6.7 Radioactive water found in tunnel containing electric cables
- 6.8 Groundwater contamination
- 6.9 Radioactive contamination of the Ocean
- 6.10 Storage tanks leaking contaminated water 2013
- 6.11 Tritium in stored water
- 7 Radioactive waste
- 8 Debris removal
- 9 Proposed building protections
- 10 Protection systems installed
- 11 Cleanup of neighboring areas
- 12 Lessons learned to date
- 13 See also
- 14 References
- 15 External links
Initially, TEPCO did not put forward a strategy to regain control of the situation in the reactors. Helmut Hirsch, a German physicist and nuclear expert, said "they are improvising with tools that were not intended for this type of situation". However, on 17 April 2011, TEPCO appeared to put forward the broad basis of a plan which included: (1) reaching "cold shutdown in about six to nine months;" (2) "restoring stable cooling to the reactors and spent fuel pools in about three months;" (3) putting "special covers" on Units 1, 3, and 4 starting in June;(4) installing "additional storage containers for the radioactive water that has been pooling in the turbine basements and outside trenches;" (5) using radio-controlled equipment to clean up the site; and (6) using silt fences to limit ocean contamination. Previously, TEPCO publicly committed to installing new emergency generators 20 m above sea level, twice the height of the generators destroyed by the 11 March tsunami. Toshiba and Hitachi had both proposed plans for shuttering the facility.
Cold shutdown was accomplished in December 11, 2011. From that point cooling was no longer required, but maintenance was still required to control large water leaks. Long term plans for Units 5 and 6 have not been announced, "but they too may need to be decommissioned".
On 5 May 2011, workers were able to enter reactor buildings for the first time since the accident. The workers began to install air filtration systems to clean air of radioactive materials to allow additional workers to install water cooling systems.
Scope of cleanup
Japanese reactor maker Toshiba said it could decommission the earthquake-damaged Fukushima nuclear power plant in about 10 years, a third quicker than the American Three Mile Island plant. As a comparison, at Three Mile Island the vessel of the partially melted core was first opened 11 years after the accident, with cleanup activities taking several more years.
TEPCO announced it restored the automated cooling systems in the damaged reactors in about three months, and had the reactors put into cold shutdown status in six months.
First estimates included costs as high as 13 billion $ (1 trillion yen), as cited by the Japanese Prime Minister at the time, Yoshihiko Noda 野田 佳彦. However, this estimate was made before the scope of the problem was known. It seems that the contamination was less than feared. No strontium is detectable in the soil, and though the crops of the year of the disaster were contaminated, the crops produced by the area now are safe for human consumption. Other studies suggest that 'nuclear waste is poisoning wildlife: Up to 99% of offspring died after eating ‘low-level’ contaminated food — “Very high” abnormality rates including “severe and rare” deformities' 
Working conditions at the plant
There has been concern that the plant would be dangerous for workers. Two workers suffered skin burns from radiation, but no serious injuries or fatalities have been documented to have been caused by radiation at Fukushima Dai-ichi.
Unskilled workforce systematically employed on Japanese nuclear power plants
The disaster in Fukushima has revealed the practice of Japanese nuclear power plants systematically using unskilled laborers with short contracts. These people are paid per day, and are hired per day from questionable agencies and firms. From data provided by NISA, it was concluded that 80 percent of all of the workforce hired in commercial nuclear power plants is done using temporary contracts, In Fukushima this number was even higher, at 89 percent. This had been practiced for decades. Unemployed people gathered in parks in the morning, and were picked up to be taken to the nuclear power plants. They would get a contract for a few months to do unskilled and the most dangerous labor. After the work was finished, these people were supposed to disappear.
Workers in dorms exposed to radiation
Two shelters for people working at the Fukushima-site were not listed as part of the radiation management zones although radiation levels in the shelters exceeded the legal limits. The consequence was, that the workers did not get paid the extra "danger allowance" that was paid to workers in these "radiation management zones". The shelters were constructed by Toshiba Corporation and the Kajima Corporation at a place some 2 kilometers west of the damaged reactors, just outside the plant compound, but quite near to the reactors 1 to 4. The shelters were built after the shelters at the plant-compound became overcrowded. At 7 October 2011 radiation levels in the Toshiba building were between 2 and 16 microsieverts per hour, in the Kajima dorm it was 2 to 8.5 microsieverts per hour. The Industrial Safety and Health Law on the prevention of health damage through ionizing radiation had set the limit for accumulated radiation dosage in radiation management zones at 1.3 millisieverts over three months, so the maximum level is 2.6 microsieverts/hour. In both dorms the radiation levels were higher. However, these doses are well below the level to affect human health. (a dental x-ray is 5 microsieverts, and on a normal day a typical person receives 10 microsieverts of radiation) According to the law, the "business operator" is responsible for "managing radiation dosage and the prevention of contamination", Toshiba and Kajima said that TEPCO was responsible. But a TEPCO official made the comment: "From the perspective of protecting workers from radiation, the business operators (that constructed the shelters) are managing radiation dosage and the prevention of contamination" in this way suggesting that Toshiba and Kajima had to take the care for the zone management.
Preventing hydrogen explosions
On 26 September 2011. after the discovery of hydrogen in a pipe leading to the containment vessel of reactor no.1 NISA instructed TEPCO to check whether hydrogen was building up in reactor no. 2 and 3 as well. TEPCO announced that measurements of hydrogen would be done in reactor no. 1, before any nitrogen was injected to prevent explosions. When hydrogen would be detected at the other reactors, nitrogen injections would follow.
After the discovery of hydrogen concentrations between 61 and 63 percent in pipes of the containment of reactor no. 1, nitrogen injections were started on 8 October. On 10 October TEPCO announced, that the concentrations were at that moment low enough to prevent explosions, and even if the concentration would rise again, it would not exceed 4 percent, the lowest level that would pose the risk of an explosion. On the evening of 9 October two holes were drilled into the pipe to install a filter for radioactive substances inside the containment vessel, this was 2 weeks behind the schedule TEPCO had set for itself. This filter should be in operation as soon as possible.
Investigations inside the reactors
On 19 January 2012 the interior of the primary containment vessel of reactor 2 was inspected with an industrial endoscope. This device, 8.5 millimeters in diameter, is equipped with a 360 degrees-view camera and a thermometer to measure the temperature at this spot and the cooling-water inside, in an attempt to calibrate the existing temperature-measurements that could have an error-margin of 20 degrees. The device was brought in by a hole at 2.5 meter above the floor where the vessel is located. The whole procedure lasted 70 minutes. The photos showed parts of the walls and pipes inside the containment vessel. But they were unclear and blurred, most likely due to water vapors and the radiation inside. According to TEPCO the photos showed no serious damage. The temperature measured inside was 44.7 degrees Celsius, and did not differ much from the 42.6 degrees measured outside the vessel.
Inspections of the suppression chambers reactor no. 2 and 3
On 14 March 2012 for the first time after the accidents six workers were sent into the basements of reactor no. 2 and 3, to examine the suppression chambers. Behind the door of suppression chamber in the no.2 building 160 millisieverts/hour was measured. The door to the suppression chamber in the no. 3 reactor building was damaged and could not be opened. In front of this door the radiation level measurement was 75 millisieverts/hour. For reactors to be decommissioned, access to the suppression chambers is vital for conducting repairs to the containment structures. Because the high levels of radiation, according to TEPCO this work should be done with robots, because these places could be hostile to humans. TEPCO released some video footage of the work at the suppression chambers of the No. 2 and 3 reactors.
On 26 and 27 March 2012 the inside of the containment vessel of reactor 2 was inspected with a 20 meter long endoscope. With this a dosi-meter was brought into the vessel to measure the radiation levels inside. At the bottom of the primary containment structure, 60 centimeters of water was found, instead of the 3 meters expected at that place. The radiation level measured was 72.9 Sievert per hour. Because of this, the endoscope could only function a few hours at this place. For reactors number 1 and 3, no endoscopic survey was planned at that time, because the actual radiation levels at these places were too high for humans.[dead link]
Because the reactor vessels and the containment buildings of Units 1, 2 and 3 are severely damaged and have lost their water tightness, it is essential for TEPCO to find an effective way to mitigate the growing volume of water that is contaminated as a result of injecting it into reactors to cool them.
In the first weeks of the aftermath, the Japanese government first requested the assistance of the Russian floating water decontamination plant Landysh to process the radioactive water from the damaged reactors. Landysh was built by Russia with funding from Japan to process liquid wastes produced during the decommissioning of nuclear submarines.
Afterwards, the French government proposed to the Japanese authorities the assistance from the French nuclear company AREVA to tackle the urgent problem of the large amounts of highly contaminated water present in the basements and the galleries connected to the damaged reactor buildings. On 15 June 2011, TEPCO began to test a radioactive water treatment system in collaboration with AREVA, Veolia Water, Silicon Valley startup Kurion, another company specializing in nuclear waste, Toshiba, and Hitachi to treat about 110 000 cubic meters of highly contaminated water, at a rate of approximately 1 200 cubic meters per day. While the contaminated water is treated, the process is expected to produce about 2 000 cubic meters of radioactive sludge by the end of 2011. TEPCO hoped to largely empty the basements of the turbine and reactor buildings of units 1-3 of contaminated water by the end of 2011. This will allow workers access to the crucial basement areas of both the turbine and reactor buildings. Workers will need access to the basements to identify the leakage paths from the containment vessels in order to finally seal the leaks, and to eventually repair the reactors' original cooling and electrical systems.
Starting this system was hampered with lots of troubles.
The device worked a long time at a much lower level that its nominal capacity. Testing started at Friday 17 June. This test was halted only 5 hours later, due to a sharp rise in radiation levels around equipment for adsorbing radioactive caesium. On 21 June TEPCO resumed testing of the system in full operation. The trial was halted shortly after the beginning because one pump automatically halted. An incorrect setting of some valve was found to be the cause later. On 22 June another incorrectly opened valve caused disruption in the ongoing test. It was found out that part of the contaminated water passed through only one of the system's three adsorbent chambers because of the faulty valve setting. The amount of highly contaminated water was growing 400 tons a day at that moment, as fresh water was used to cool the reactors.
On 24 June TEPCO announced that the trouble-hit decontamination system was working as planned by reducing the concentration of radioactive substances remaining in the water to the target ratio of one-to-100,000. However, the test run was stopped as the device for adsorbing radioactive caesium still worked only at one-tenth its capacity. TEPCO said resuming full operation of the decontamination system could take several more days. The next day on 25 June the pump of the salt-removal device (reverse osmosis) failed. On 26 June TEPCO announced to start full-scale operation would start on the following day. The faulty decontaminating devices were fixed by using a different adsorbent material. Some 5,400 tons of water was cleaned during the test runs, and the contaminated water that was about to fill the reactor buildings could be transferred.
On 27 June TEPCO started cooling the reactors with decontaminated water. About 1,850 tons water were reprocessed. The system was halted only one and a half hours later after discovering water leaking from the pipes. However, water was found leaking from unfastened pipes. A TEPCO-operator said, that they failed to check the 4 kilometers of piping, because during an inspection more than 2 weeks before there was no problem found. By 28 June, it was reported that the system had already treated approximately 7 230 cubic meters of contaminated water. On 29 June the system was restarted again, however due to leaking contaminated water storage tank it was stopped again.
On 6 July the system was running at 80% of the desired capacity for recycling the cooling-water. On Sunday 10 July and Tuesday 12 July the system had to be stopped for hours because of leakages of chemicals and highly contaminated water. On 13 July the system still operated only at 73% of its nominal capacity On 24 July around noon the decontamination-unit had to be stopped, an alarm of the desalinization unit went off. Another unit was installed, but this had only half the capacity of the removed unit. Sunday evening the whole decontamination-unit could be restarted. Injection of fresh water from a nearby dam was needed to make up for the shortage of water to cool the reactors. Because of these troubles the amount of highly contaminated water in the plant was rising again.
On 26 July the unit was still not working to expectations and TEPCO announced that yet another system, named SARRY (simplified active water retrieve and recovery system) was to be installed consisting of 14 cylindrical tanks containing minerals. SARRY was designed to reduce radioactive substances in water, such as cesium, to less than one millionth. On 25 July the first tanks and other parts were shipped from Iwaki, Fukushima to the plant. SARRY was to be put into service at the beginning of August, besides the already installed decontamination-system that as a whole was operating with low reliability. At that moment the operating rate was 53 percent, significantly below the goal of 90 percent.
On 2 August the amount of contaminated water in the basements of the plant had risen to 21.000 tons. According to TEPCO the water-treatment system that had been installed had only a limited capacity only 40 percent of the contaminated seawater could be processed into freshwater, leaving 60 percent untreated. TEPCO had been testing a new system which could reduce 80 tons of saltwater to about 50 tons each day, by evaporating the saltwater. The steam was condensed and recycled to freshwater to be used for cooling the reactor. Two units were put into actual operation on Sunday 7 August, after the testing was completed. Six more additional units were planned to be operational by October.
On 4 August 2011 a pump in the water-treatment-system stopped, and on 5 August the system halted after an alarm went off. On Sunday 7 August at 8 AM the filtering system came to a halt again. Shortly after 7 AM, some of the pumps in a US decontamination device, used to remove radioactive cesium, stopped and could not be restarted. About an hour later, a pump in a French device also stopped working. A back-up pump also failed to work, this brought the whole decontamination system to a halt. The injection of cooling water was continued using treated water. A Japanese-made decontamination device had been added by TEPCO to the system in the hope to make it more stable. But TEPCO wanted to treat wastewater before the test run of the new device, because there was only very limited storage space left available for contaminated water at the plant at that time. On 10 August the filter-system still worked only at 66 percent of its nominal capacity of 90 percent. Yoshinori Moriyama, the chairman of nuclear disasters at the Nuclear Safety Commission, said that TEPCO should improve the system by pinpointing the common root of problems, rather than addressing them ad hoc. Without improving the performance there was still the possibility that radioactive materials would be spilled outside the compound.
On August 18, 2011 a Japan-made decontamination unit was taken into service after a successful tryout, that started on August 16: It consist of 14 cylindrical tanks containing zeolite, to absorb cesium and other radioactive isotopes from the highly radioactive water that accumulated at the plant. This second system would function aside the already installed water-decontamination-system.
On 28 August 2011 2 TEPCO workers at the plant were exposed to radiation by mistake while they were replacing parts of the contaminated water processing system. The next Wednesday 31 August two other workers were sprayed with highly contaminated water when the water splashed from a container with a leaking valve that did not close. It was found that they were exposed to 0.16 and .14 millisieverts. The last man wore a raincoat. No immediate symptoms were found. On September 2, TEPCO reported another worker was sprayed on the same day. This incident prompted Japan's Nuclear and Industrial Safety Agency to ask TEPCO to improve safety measures for workers at the plant.
In the beginning of September 2011 the operating rate of the filtering system exceeded the target of 90 percent for the first time. On 11 September an amount of 85,000 tons of water had been decontaminated so far, over 100,000 tons of waste-water remained to be treated. But the nuclear waste generated by the filters filled already almost 70 percent of the 800 cubic meter storage space available. TEPCO was in need to rethink how to cool the reactors with less than 15 tons water per day, in order to reduce the growth of waste-water and nuclear waste.
On 1 November, MP Yasuhiro Sonoda became internationally known for drinking a glass of water, collected from puddles under the reactor buildings at the plant, during a press conference to prove the safety of the installed decontamination procedures.
TEPCO warned after recurrent leakage of radioactive strontium-contaminated water
At the beginning of December 2011, another leak was found in the desalination plant at the facility. As on 5 December some 45 tons of water heavily contaminated with radioactive strontium escaped, of which 150 liters of water found its way into the ocean through a ditch connected with the beach. Within 10 days another leak was found: 30 liters had escaped from the piping, but according to TEPCO it had remained on the plant. The outflow stopped after the valves were closed. Because of this NISA sent a stern warning to the operator of the plant, requiring TEPCO to investigate the cause of the leaks and prevent them in future.
On 5 April 2012 at 1.00 AM a leaking pipe was found. The leakage stopped an hour after the valves were closed. 12,000 liters water with high levels of radioactive strontium were lost, according to TEPCO much of this water escaped through a nearby sewer-system into the ocean. Investigations should reveal how much water was lost into the ocean, and how the joint could fail. A similar leakage in at the same facility happened on 26 March 2012.
Water in the basement
As illustrated in the diagram to the right, the Fukushima I nuclear plant has a number of trenches and pipe tunnels that stretch from each unit's reactor (diagram #1), to the unit's turbine building (diagram #2), to the sea (to the right of diagram #6). In some locations these connections are open trenches, while in other locations the connections are pipe tunnels.
During work to restore power to Unit 2 on 27 March, TEPCO reported very high levels of radiation in water in the basement of the Unit 2 turbine building. While first reported radiation levels of more than 10 million times usual appeared later to be erroneous, the radiation measurements were more than 100,000 times higher than usual. On 28 March, the Nuclear Safety Commission announced its suspicion that "radioactive substances from temporarily melted fuel rods at the No. 2 reactor had made their way into water in the reactor containment vessel and then leaked out through an unknown route". Highly radioactive water was later found in trenches at three of the units. These trenches stretch toward, but do not directly connect to, the sea (see diagram #6). On 30 March, the Units 2 and 3 trenches were 1 m below the level at which they would overflow into the sea. In comparison, the Unit 1 trench was 10 cm from overflowing.
The high levels of water in the trenches combined with their potential to overflow to the sea complicated the cooling efforts because the water required to cool the reactor was believed to also be filling the trenches. Hence, cooling Unit 2 with large quantities of fresh water was expected to cause the trenches, leading to the sea, to fill and overflow—worsening the radioactivity release. Consequently, TEPCO reduced the amount of water injected into Unit 2 from 16 to 7 ton per hour. TEPCO used two approaches to prevent the highly radioactive water from leaking into the sea.
Pumping the water from the basement
The first approach to prevent tunnel water from leaking into the sea was to pump the tunnels dry. Beginning on 27 March, operators attempted to pump water from the turbine hall basement (see the tunnel below diagram #2) to the condenser (the large black vessel). By pumping water out of the basement, TEPCO expected to lower the trench water level, and reduce the likelihood of overspill to the sea. However, "both condensers turned out to be full", which prevented pumping. Therefore, pumps able to shift 10 to 25 tons of water per hour were used to move condenser water to storage tanks, freeing condenser storage for water that was in the basement of Unit 2. However, since both the storage tanks and the condensers were nearly full, TEPCO also considered using tankers or a "mega float" as a temporary storage location for the radioactive water. Regardless of the availability of offshore storage for radioactive-contaminated water, TEPCO decided to pump its least contaminated water, approximately 100 times the legal limit, from a wastewater treatment plant, out to sea on 5 April to free storage space.). At the same time, on 5 April, TEPCO began pumping water from the unit's condensers of Units 1–3 to their respective condensation storage tanks to free room for the trench water.
Plugging the source of the water
The second approach used by TEPCO to limit overflow into the sea was to plug leaks into pits that were connected to the trenches. Eventually, leaks would be discovered in pits in Unit 2 (discovered 1 April) and Unit 3 (discovered 11 May). While the later found leak in Unit 3 was reported to be plugged within one day, the Unit 2 pit-leak took much longer to stop.
Discovered on 1 April, the leak in the Unit 2 pit was located near the Unit 2 reactor basement and above the trench system. The crack in the pit was reported at the time to be the primary source of water to the trench system; however, at that time, the Unit 3 leak was unknown. TEPCO reported the Unit 2 leak was from a crack 20 cm in size, and that it may have been leaking since the magnitude 9 earthquake shook the plant on 11 March until finally patched on 6 April. However, radiation levels above the pit exceeded 1000 mSv/h (1 Sv/h, 100 Rem/h), hampering technicians to safely work. Regardless, TEPCO attempted to use sandbags and concrete to plug the leak. However, by 2 April, TEPCO acknowledged the water was still leaking into the trenches and to the sea. On 2 April, TEPCO said that it had again attempted to plug the hole, now using 2,000 liters of a synthetic resin. TEPCO attempted to inject a polymeric water absorbent, used for diapers, into pipes leading to the pit; this absorbent was also coupled with sawdust and shredded newspapers. However, on 3 April and 4 April, this approach appeared to have failed to slow the leak, leading TEPCO to use a colored dye to confirm the location and size of the leak. The dye indicated the leak was from a cracked pipe and seeping through gravel into the pit. On 5 April, TEPCO began using liquid glass to attempt to stop the leak. Finally, on 6 April, TEPCO drilled a hole into the pit near Unit 2 and injected water glass (sodium silicate) into the pit. The residual heat carried by the water used for cooling the damaged reactors accelerated the setting of the injected mixture. Shortly afterward, TEPCO announced that water had stopped leaking from the pit.
In an attempt to prevent future leaks, TEPCO installed seven steel plates at Unit 2 that would prevent water from flowing out the plant's water intakes (see diagram #6). Additional plates were expected to be added at the other Fukushima units. However, these plates were later suspected of "stirring up" radioactive debris, and to have significantly increased radiation measured in the sea. Long term, TEPCO is "also considering pouring adhesive concrete into the suppression chamber of Reactor 2 to patch the hole that is believed to be causing radioactive water to leak into the turbine building and the trench." On 21 April, TEPCO estimated that 520 tons of radioactive water had leaked into the sea before the leaks were plugged, releasing 4,700 TBq (20,000 times facility's annual limit). TEPCO did not estimate the amount of water that escaped from the Unit 3 leak, but did say the leaked water was contaminated with iodine-131, caesium-137 and caesium-134 far beyond regulatory limits, and that the leak was patched the same day it was discovered.
With the leak plugged, at least temporarily, on 10 April 2011, TEPCO returned to the work begun on 27 March, removing water from the tunnel system so repairs could be made to the plant's original cooling system. Removal is considered essential because the water is so radioactive, in excess to the 1000 mSv/h measuring equipment's range, that repair work cannot be safely conducted without removing the water.
By 13 April, TEPCO had pumped approximately "250 tonnes of highly radioactive water from the trench into the unit's turbine condenser", lowering the trench water-level by 4 cm. The water was approximately 99 cm deep originally. TEPCO estimated that pumping would take "about 40 hours to move some 700 tonnes of water from the trench". Water would eventually have to be removed from the Unit 2 basement, as well as from the trenches and basements of Units 1 and 3.
By 15 April, TEPCO estimated that 660 tons of 60,000 tons of the highly radioactive water had been pumped from the trenches. The water level was believed to have fallen by 8 cm, and TEPCO announced it expected to start storing some of the trench water in storage spaces freed up by dumping 9,100 tons of slightly contaminated water from a wastewater treatment plant from 4 April to 10 April. However, shortly after announcing the reduction in level, the water level began increasing again, a 2.5 cm increase on 16 April, and a 3 cm increase on 17 April were believed to have been caused by the earlier efforts to patch leaks to the ocean.
Then, on 20 April, TEPCO began pumping the basement water to the wastewater treatment facility.
By 27 April, TEPCO had pumped 1.89 million liters of the highly contaminated water to the processing plant, and announced plans to add more pumping capability. While progress was being made on pumping the Unit 2 basement, on 14 May, TEPCO announced that it appeared that the Unit 1 basement is also "half full" of radioactive water that was expected to delay cleanup efforts.
On 15 May, TEPCO announced plans to pump approximately 4,000 tons of 22,000 tons contaminated water from the Unit 3 turbine building basement and trench system; the water was 1.4 m high in the basement.
At 20 September 2011 from 10:00 am to 4:00 pm the accumulated water from the turbine building of Unit 6 was pumped to temporary tanks. At 21 September from 10:00 am the pumping was restarted.
In the evening of 21 September the arrival of typhoon Roke was forecast. Precautions were taken, the installation of steel plates at the plant's water intake area was halted, and also the work on the decontamination of seawater. The work on the cover of reactor 1 was suspended because the strong winds. Outdoor piping and pumps for injecting water into the reactors were secured with ropes to keep them from being knocked over by the wind. Although up to 250 millimeters rainfall was expected, TEPCO did not fear any overflow of radioactive wastewater from the reactor turbine buildings.
Underground wall to prevent contamination of the ocean
On 6 September 2011 TEPCO announced the plan to build an iron wall on the ocean side of the plant to prevent the leakage of radioactive water into the sea. At that time some 110,000 tons of highly radioactive water remained in the basements of the plant. It was feared that this water could contaminate the groundwater and contaminate the ocean-water. Thousands of iron pipes, 22 meter long and 20 centimeters wide, would create an 800-meter-long wall around the water intakes of 4 reactor facilities, deep below the sea bed to stop the flow of groundwater. The level of underground water was monitored with care, and to prevent overflow groundwater would be pumped away. Constructions were to be started at the end of the year 2011 and should be completed in about 2 years time.
Influx of groundwater
According to TEPCO, large amounts of groundwater might be entering through cracks in walls into the basements of the reactor buildings. TEPCO calculated that this could be some 200 to 500 tons daily. This would increase the amount of highly radioactive water that had accumulated in the buildings.
TEPCO said it planned to keep levels of radioactive water lower than the groundwater to stop the inflow. NISA said that this groundwater influx should be taken into account with long-term decontamination plans.
Building a frozen wall, enlarging the storage for contaminated water
On 30 May 2012, the Japanese government ordered TEPCO to built a wall around the reactor buildings to limit the influx of groundwater. A wall of 1.4 kilometer long of frozen soil, 30 meters deep, with pipes that run coolant, should be operational from the first half of the Japanese fiscal year 2015. This method was originally proposed by Kajima Corp., but TEPCO feared that accumulating radioactive water inside the buildings might seep out of the buildings when the water pressure changed. The cost of the system was unknown, but was estimated to be some tens of billions of yen. On top of this, the government ordered TEPCO to build tanks up to a total of 800,000 tons to store radioactive water, to be completed by the end of fiscal 2016. At the end of May 2012, the capacity was 330,000 tons.
Slightly radioactive water found under the waste water treatment facility
On 18 December 2011, a worker discovered some 230 cubic meters of radioactive water in a 54 meters long tunnel under the waste-water processing plant. The water-level varied from half a meter to 3 meters deep. Radiation levels measured 3 millisievert per hour, just a fraction of the radiation-level of the highly contaminated water that was stored above this tunnel. This level of radiation is marginal and not dangerous. TEPCO investigated the source of the water and found that most likely, some water had flowed into the tunnel from the storage above and had been diluted afterwards by incoming groundwater. According to TEPCO, this tunnel had no connection to the sea. The discovery did, however, raise questions about the inspections and management-capabilities of TEPCO because it failed to notice the water in the tunnel after the water-treatment facility was completed.
In the first week of January 2012, TEPCO discovered another tunnel filled with 142 cubic meters of radioactive contaminated water, containing 100 becquerels of cesium per liter. According to TEPCO, no water leaked into the ocean from that site. The tunnel was situated under the waste-water-treatment factory at the plant. TEPCO suspected that rainwater leaked into the tunnel and became contaminated with radiation.
Radioactive water found in tunnel containing electric cables
On 11 January 2012, radioactive contaminated water was found in two underground tunnels. On 12 January TEPCO admitted that around 300 cubic meter water had accumulated in an underground tunnel near reactor No.3, with electric cables. Radioactive cesium was measured in concentrations varying from 49 to 69 becquerels per cubic centimeter. This is a very low amount of radiation. Smaller amounts of contaminated water with lower concentrations cesium was found in a tunnel near reactor no.1. How the water could accumulate at these places was still under examination.
On 19 January 2012, 500 tons of highly contaminated water in a pit near the No.2 reactor at a facility to store highly contaminated water. The pit had a valve which was used for pumping in seawater. This water had 16,200 becquerels of radioactive cesium per cubic centimeter. The highest level of radioactive substances found in this survey. Another 600 tons of water containing 860 becquerels of radioactive elements per cubic centimeter was found in a pit near the No.3 reactor, this is a very low level of radioactivity. According to TEPCO it was unlikely that water from these pits could flow into the ocean, because there no change of contamination was found. How the water could flow into the tunnels was still under investigation.
On 8 July 2013, TEPCO found 9,000 becquerels of cesium-134 per liter and 18,000 becquerels of cesium-137 per liter in a sample taken from a well close to the coastline. Compared with samples taken three days earlier, the levels were 90 times higher. The cause was unknown. The well is situated close to a well that was leaking highly radioactive water into the sea in April 2011. In another well, situated about 100 meters south of the first well, a sample of groundwater showed that the radioactivity had risen 18 times in 4 days; 1700 becquerels per liter strontium and other radioactive substances. A day later the readings in the first well were 11,000 Bq/L Ce-134 and 22,000 Bq/L Ce-137, 111 times and 105 times greater than the samples of 5 July. TEPCO did not know the reasons for the higher readings, but the monitoring was to be intensified.
More than a month after the first discovery of the groundwater contamination, TEPCO made a start to contain the radioactive groundwater. They assumed that the radioactivity had escaped early in the beginning of the disaster in 2011, but NRA-experts had serious doubts about their assumption. According to them, other sources could not be excluded. Numerous pipes were running everywhere on the reactor grounds to cool the reactors and decontaminate the water used, and leaks could be anywhere. This solution might easily redirect the groundwater flows, and spread the contamination even more. Besides that, TEPCO had plans for pumping groundwater. At that time the turbine-buildings of reactor nr.2 and nr.3 contained 5000 and 6000 cubic meter highly radioactive water. With wells in contact with the turbine-buildings, this could spread the radioactivity into the ground. The NRA announced that it would form a task force to find the leaks and to block the flow of the groundwater to the coastline, because the NRA suspected that the groundwater was leaking into the sea.
On 22 July, a day after the Japanese elections for the Upper House, TEPCO admitted that radioactive groundwater was leaking into the ocean.
On 27 July 2013, TEPCO announced that extremely high levels of tritium and cesium were found in a pit containing about 5000 cubic meters water on the seaside of the unit 2 reactor building. 8.7 million becquerels/liter tritium was found and 2.35 billion becquerels/liter cesium. The NRA was concerned that leaks from the pit could release high tritium levels into the sea and that there was still water flowing from the reactor into the turbine building and into the pit. However, TEPCO believed that this pollution was there from the first days in 2011, and stayed there. Nevertheless, TEPCO would control the site for leaks, and seal the soil around the pit.
Radioactive contamination of the Ocean
In July 2013, it was revealed TEPCO had been aware that radioactive water has been leaking into the ocean for 2 years, but that problems regarding radioactive groundwater have been ignored. In August, TEPCO admitted that up to 400 tons of contaminated water flows into the Pacific Ocean every day and that an estimated 20 to 40 terabecquerels of tritium was lost into the sea since May 2011. Under its safety regulations and normal circumstances, TEPCO was allowed to dump 22 terabecquerels per year, but TEPCO admitted that there was no control and it was unknown when the tritium loss had started. TEPCO had built an underground wall using liquid glass to make the soil impermeable to water, although the NRA had some doubts about the plan. The groundwater level was rising fast, and the amount of water flowing in the direction of the ocean was still the same. Measurements showed that deeper layers of groundwater contained more radioactivity. On 10 August 2013, TEPCO revealed that although the underground wall was completed on 9 August, radioactive water was "probably" flowing over the top of the underground wall (on 1.8 meters under the surface). This was proven by measurements in both sea and groundwater. TEPCO started pumping groundwater, although this did not stop the leakage. The total groundwater flow was estimated at about 1000 tons, about 400 tons of this was flowing into the reactor buildings, and from there the water could still leak into the ground from a maze of pipes and tunnels.
Storage tanks leaking contaminated water 2013
On 19 August 2013, two highly toxic puddles were found near the storage tanks for contaminated water. According to TEPCO, some 300 tons of highly contaminated water had leaked from a 1000 ton cylindrical steel storage tank. The water inside the puddles was emitting 80 million becquerels per liter. 100 millisieverts per hour was detected near the surface of one of the puddles. (For comparison, the maximum allowable exposure in Germany for people working in radioactive environments is 20 millisieverts per year). On 20 August the source of the water still had not been found. The incident was provisionally rated by the NRA as a Level 1 “anomaly” on the eight-level International Nuclear and Radiological Event Scale. TEPCO was instructed to identify the place where the tank was leaking, and to collect the contaminated soil. 
From July 2012 to July 2013, the NRA secretariat advised TEPCO to improve its surveillance on the storage tanks for contaminated water. According to the NRA, there were no gauges in the tanks to monitor the water levels. The 30 tanks were only inspected visually, twice a day, by 2 to 9 workers; with 450 tanks checked by each worker in 2 or 3 hours. A NRA-inspection found a crack in a barrier meant to stop leaked water. To be able to detect leakages soon after they might occur, TEPCO was urged to increase the number of inspections to by a factor of ten. TEPCO answered, saying that improvements had been made, but the patrols were only doubled; no additional staff was hired, no surveillance cameras were installed, and no gauges were installed. On rainy and snowy days, no patrols were made This made it possible for the leakage of the 300 tons or water. This leak went on for almost a month before it was detected. In August 2013, TEPCO was urged again to make improvements. TEPCO increased its patrol staff by 50 people, 4 daily inspections, and promised to install gauges in the tanks to monitor the water levels inside. Initially two workers were assigned to check more than 1,000 storage tanks on the site. Neither of the workers carried dosimeters. Radiation near a pipe connecting two other tanks had been measured at 230 mS. Radiation near tank was measured as 18 times higher than previously thought.
The walls of the leaking tank were made of steel plates joined together with bolts or flanges. The decision to use this type of tank was made because of a lack of workforce and the haste to install the tanks. The plant contains around 350 of these flange tanks, which are vulnerable to leakage, and have short life cycle of 5 years. After installation the storage tanks were only checked once for proper placement, and alignment. In July 2011, TEPCO found the concrete floor under the new tanks had hardened and cracked, and that it had sunk 20 cm. The tanks were disassembled and moved to a new location. After the tanks were moved, only limited measurements were done before they went into service.
On 26 August 2013 TEPCO announced that the water inside the leaking tank contained 44,000,000 Bq/m3 of Cs-134 and 92,000,000 Bq/m3 of Cs-137. However, 46,000,000 Bq/m3 of Cs-134 and 100,000,000 Bq/m3 of Cs-137 were found on 19 August 2013. TEPCO gave no explanation for this difference.
On 28 August 2013, a subcontractor employee was contaminated on his face, head and chest while transferring water from the damaged tank. After decontamination, 5,000 cpm were still measured on his head; the readings before "wiping the contamination" were kept secret. The man was released, but ordered to have a whole body count later.
On 28 August 2013 prime minister Shinzo Abe said that the Japanese government would take a leading role in the matter. TEPCO should not be alone in charge, but be helped to overcome the difficulties. The same day, industry minister Toshimitsu Motegi said, that taxpayer money could be used to expand the - not yet operational - ALPS, the experimental 3 channel-machine designed to extract all radioactive contamination, except Tritium.
On 29 August the NRA ordered a more comprehensive effort to monitor the ocean near the plant.
On 2 September it was reported that radiation near another tank was measured at 1,800 millisieverts an hour, 18 times higher than previously thought. TEPCO had initially recorded radiation at about 100 millisieverts an hour, but later admitted that that was because the equipment they were using could only read measurements up to that level. The latest reading came from a more advanced device capable of measuring higher levels. The buildup of water at the site is close to becoming unmanageable and experts say that TEPCO will soon be left with no choice but to release the water into the ocean or evaporate it.
The Japanese government gave $473m (£304m) public funding to tackle the problem of the electricity company TEPCO on 3 September 2013, when radiation near tanks rose 2,200 millisieverts per hour (mSv/h).
On 5 September, Tatsujiro Suzuki, vice chair of the Japan Atomic Energy Commission, resumed his regular (sometimes daily) updates of the situation at Fukushima for the Bulletin of the Atomic Scientists.
On 9 September TEPCO started cleaning the draining ditch at the north side of the leaking tank. One day before Tokyo was selected as host of the 2020 Olympic Games. Radiation monitoring data were masked after that day for some time. TEPCO did not mention any relation between the Olympic games and the sudden cleaning.
On 12 September 2013 TEPCO released new data recording the contamination around the failing storage tank, following the 300 tons leakage. Tritium levels kept rising in a test well 20 meters north from the tank:
- 4,200 bq/l on 8 September
- 29,000 bq/l on 9 September
- 64,000 bq/l on 10 September
- 97,000 bq/l on 11 September
Experts assumed the tritium in the well originated from the leaking tank.
Near the H4 area, in a drainage ditch directly connected to the ocean, 220 bq/l was found on 12 September 2013 at 150 meters distance of the coast. The radiation of strontium, cesium and other beta-emitters had risen 12 times compared with the levels found on 10 September at the same spot. TEPCO assumed that water was leaking along the sandbags, that should prevent any further leakage of contaminated water. These findings did contradict the assurances Prime Minister Shinzo Abe's made during Tokyo's final presentation to the International Olympic Committee in Buenos Aires, that the leakage of radioactive water had been "completely confined" to waters 0.3 square kilometers from the plant. The findings raised some doubts about the possibility to "bypass" the groundwater along the contaminated areas around the reactors, because the contamination from the leaking tank was situated 130 meters west from the planned frozen dam.
Tritium in stored water
In January 2014 it was made public that a total of 875 trillion becquerel (Bq) of tritium are on the site of Fukushima Daiichi; it would take 59 years to safely discharge this amount of tritium to the sea. According to data that TEPCO submitted to the Tritium task force (of the Ministry of Economy, Trade and Industry) 400,000 tonnes of contaminated water – which are stored in tanks – contain about 817 trillion Bq of tritium. Further 58 trillion Bq of tritium are contained in water outside of tanks, e.g. in reactor buildings. According to further data submitted by TEPCO, the amount of tritium contained in the contaminated water is increasing by approx. 230 trillion bq per year. This followed a report made public in December 2013 that "Tritium could be separated theoretically, but there is no practical separation technology on an industrial scale."[dubious ]
Cooling the reactors with recirculated and decontaminated water from the basements proved to be a success, but as a consequence, this radioactive waste was piling up in the temporary storage facility at the plant. TEPCO decided in the first week of October to use the "Sally" decontamination system built by Toshiba Corporation and keep the Kurion/Areva system as back-up.
On 27 September after three months operation some 4,700 drums with radioactive waste had piled up at the plant. The Kurion and Sallysystems both utilized zeolites to concentrate cesium. After the zeolite was saturated, the vessels with the zeolite were turned into nuclear waste. By now, 210 Kurion-made vessels with a total of 307 cubic meters, each vessel measuring 0.9 meters in diameter and 2.3 meters in height had accumulated at the plant. The Areva-filters used sand to absorb radioactive materials and chemicals were used to reactivate the filters. In this way, 581 cubic meters of highly contaminated sludge were produced.
According to Professor Akio Koyama of the Kyoto University Research Reactor Institute, the density of high-level decontaminated water was believed to contain some 10 billion becquerels per liter, but if this is condensed to polluted sludge and zeolites, this density could increase 10,000 fold. These densities could not be dealt using conventional systems.
Spent fuel pools
On August 16, 2011, TEPCO announced the installation of devices in the fuel-pools of reactor 2, 3 and 4, which used special membranes and electricity to desalinate the water. These pools were cooled with seawater for some time, and TEPCO feared the salt would corrode stainless steel pipes and the pool walls. First the nr. 4 fuel pool was installed, the pools of reactor 2 and 3 came next. TEPCO expected to be able take away 96% of all the salt within two months after the start of this operation.
Unit 4 spent fuel removal
On December 22, 2014, TEPCO crews completed the removal of all fuel assemblies from the fuel-pool of reactor 4. The fuel assemblies, 1535 in all including used and new fuel, were moved to the ground-level Common Spent Fuel Pool, except for under 200 unused fuel assemblies which were moved to the fuel-pool of reactor 6.
On 10 April 2011, TEPCO began using remote-controlled, unmanned heavy equipment to remove debris from around reactors 1–4. The debris and rubble, caused by hydrogen explosions at reactors 1 and 3, was impeding recovery operations both by being in the way and emitting high radioactivity. The debris will be placed into containers and kept at the plant.
Proposed building protections
|This section is outdated. (August 2011)|
Because the monsoon season begins in June in Japan, it became urgent to protect the damaged reactor building from storms, typhoon and heavy rainfall. As a short term solution, TEPCO envisaged to apply a light cover on the remaining structures above the damage reactors. As of mid-June TEPCO released its plan to use automated cranes to move structures into place over the reactor. This strategy is an attempt to keep as many people away from the reactors as possible while still covering the damaged reactors.
On 18 March, Reuters reported that Hidehiko Nishiyama, Japan's nuclear agency spokesman when asked about burying the reactors in sand and concrete, said: "That solution is in the back of our minds, but we are focused on cooling the reactors down." Considered a last-ditch effort since it would not provide cooling, such a plan would require massive reinforcement under the floor, as for the Chernobyl Nuclear Power Plant sarcophagus.
Scrapping reactor Daiichi 1, 2, 3, 4
On 7 September 2011 TEPCO president Toshio Nishizawa said, that the 4 damaged reactors will be scrapped. This announcement came at a session of the Fukushima Prefectural Assembly, which was investigating the accident at the plant. Whether the six other remaining reactors, (Daiichi 5, 6, Daini 1, 2, 3, 4) should be abolished too, this decision would taken based on the opinions of local municipalities,
On 28 October 2011 the Atomic Energy Commission of Japan presented a timetable in a draft report, how to scrap the Fukushima reactors. Within 10 years a start should be made with the retrieval of the melted fuel of the reactors. First the containments of reactor 1, 2 and 3 should be repaired, than all should be filled with water, to prevent radiation releases. Decommissioning would take more than 30 years, because the pressure vessels of the reactor vessels are damaged too. After the accident at Three Mile Island in 1979, some 70 percent of the fuel rods had melted. There the retrieval of the fuel was started in 1985, and completed in 1990. The work at Fukushima was expected to take more time because of the far greater damage, and the fact that 4 reactors would need to be decommissioned at the same time.
After discussions were started in August 2011, on 9 November a panel of experts of the Japan's Atomic Energy Commission completed a schedule for scrapping the damaged reactors, their conclusions were:
- the scrapping will take 30 years or longer
- first the containment vessels needed to be repaired, and filled with water to block radiation.
- the reactors should be in a state of stable cold shutdown
- three years later a start would be made to take all spent fuel from the 4 damaged reactors to a pool inside the compound
- within 10 years the removal of the melted fuel inside the reactors could start
This scheme was partly based on the experience with the 1979 Three Mile Island accident, however in Fukushima with three meltdowns at one site the damage was much more extensive. It could take 30 years or more to remove the nuclear fuel, to dismantle the reactors, and to remove all buildings. Research institutions all over the world were asked to participate in the construction of a research-site to examine the removal of fuel and other nuclear wastes. The official publication of the report was planned at the end of 2011.
Protection systems installed
Since the disaster, TEPCO has installed sensors, a fabric cover over the reactors and additional filters to reduce the emission of contaminants.
Sensors for xenon and temperature changes to detect critical reactions
After the detection of radioactive xenon gas in the containment vessel of the No. 2 reactor on 1 and 2 November 2011 TEPCO was not able to determine whether this was a sustained fission process or only spontaneous fission. Therefore TEPCO installed detection devices for radioactive xenon to single out any occurrence of nuclear criticality. Next to this TEPCO installed temperature sensors to control temperature changes in the reactors, another indicator of possible critical fission reactions.
On 20 September the Japanese government and TEPCO announced the installation of new filters to reduce the amount of radioactive substances released into the air. In the last week of September 2011 these filters were to be installed at reactor 1, 2 and 3. Gases out of the reactors would be decontaminated before they would be released into the air. Mid October the construction of the polyester shield over the No.1 reactor should be completed. In the first half of September the amount of radioactive substances released from the plant was about 200-million becquerels per hour, according to TEPCO, that was about one-four millionths of the level of the initial stages of the accident in March.
Fabric cover over Unit 1
An effort has been undertaken to fit the three damaged reactor buildings with fabric covers and filters to limit radioactive contamination release. On 6 April 2011, sources told Kyodo News that a major construction firm was studying the idea, and that construction wouldn't "start until June". The plan has been criticized for potential only having "limited effects in blocking the release of radioactive substances into the environment". On 14 May, TEPCO announced that it had begun to clear debris to create a space to install a cover over the building of reactor 1. In June, a large crane was erected near Reactor 1 to begin construction of the fabric cover. From mid August to mid September 2011, a rectangular steel frame entirely surrounding the reactor building was constructed. Starting 9 September, the crane was used to attach polyester panels to the frame. On 20 September 2011, TEPCO announced that within three weeks they hoped to complete the construction of the polyester shield over the No.1 reactor. By that time the steel frame for the fabric cover had been completed. By 7 October, the roof of the structure was being added. On 9 October, the walls of the cover appeared to be placed, and by 13 October the roof had been completed.
Cleanup of neighboring areas
Significant efforts are being taken to clean up radioactive material that escaped the plant. This effort combines washing down buildings and scraping away topsoil. It has been hampered by the volume of material to be removed and the lack of adequate storage facilities.
There is also a concern that washing surfaces will merely move the radioactive material without eliminating it.
After an earlier decontamination-plan only to clean all areas with radiation levels above 5 millisievert per year, had raised protests, the Japanese government revealed on 10 October in a meeting with experts a revised decontamination plan. This plan included:
- all areas with radiation levels above 1 millisievert per year would be cleaned.
- no-entry zones and evacuation zones designated by the government would be the responsibility of the government.
- the rest of the areas would be cleaned by local authorities.
- in areas with radiation levels above 20 millisievert per year, decontamination would be done step by step.
- within two years, radiation levels between 5 and 20 millisieverts should be cut down to 60%.
- the Japanese government would help local authorities with disposing the enormous amount of radioactive waste.
On 19 December 2011 the Japanese Ministry of Environment published more details about these plans for decontamination: the work would be subsidized in 102 villages and towns. Opposition against the plan came from cattle-farmers in the prefecture Iwate and the tourist-industry in the city of Aizuwakamatsu, because of fears that cattle sales might drop or tourism would be hurt to the town, when the areas would be labeled to be contaminated. Areas with lower readings complained that their decontamination would not be funded.
In a Reuters story from August 2013, it was noted "[m]any have given up hope of ever returning to live in the shadow of the Fukushima nuclear plant. A survey in June showed that a third of the former residents of Iitate, a lush village famed for its fresh produce before the disaster, never want to move back. Half of those said they would prefer to be compensated enough to move elsewhere in Japan to farm." In addition, despite being allowed to return home, some residents say the lack of an economy continues to make the area de facto unlivable. Compensation payments to those who have been evacuated are stopped when they are allowed to return home, however, as of August 2013 decontamination of the area has progressed more slowly than expected. There have also been revelations of additional leaks (see above: storage tanks leaking contaminated water).
Cementing the seabed near the water-intake
On 22 February 2012 TEPCO started cementing the seabed near the plant to prevent the spread of radioactive materials into the sea. Some 70000 square meters of seabed around the intake of cooling water would be covered with 60 centimeters thick cement. The work should be finished within 4 months time, and prevent the spread of contaminated mud and sand at that place for at least 50 years.
New definition of the no-entry-zones introduced
On 18 December 2011 Fukushima Gov. Yuhei Sato and representatives of 11 other municipal governments near the plant were notified at a meeting at the city of Fukushima the three ministers in charge of handling the crises, Yokio Edano, minister of Economy, Trade and Industry, Goshi Hosono, nuclear disaster minister, and Tatsuo Hirano, minister in charge of reconstruction of the government plan to redesign the classification of the no-entry-zones around the Fukushima nuclear plant. From 1 April 2012 a three level system would be introduced, by the Japanese government:
a) no-entry zones, with an annual radiation exposure of 50 millisieverts or more
- at these places habitation would be prohibited
b) zones with annual radiation exposures between 20-50 millisievert,
- here former resident could return, but with restrictions.
c) zones with exposures of less than 20 millisievert per year
- in these zones the residents would be allowed to return to their houses.
Decontamination efforts were planned in line with this newly designed order, to help the people to return to places where the radiation levels would be relatively low.
Costs of the clean-up operations
Mid December 2011 the local authorities in Fukushima had spent already around 1.7 billion yen (21 million$) on the costs of decontamination-works in the cities of Fukushima and Date and the village of Kawauchi. The total clean-up costs were estimated around 420 billion yen (~ 5.2 billion$). For the clean-up only 184.3 billion yen was reserved in the September supplementary budget of prefecture Fukushima, and some funds in the central government's third supplementary budget of 2011. Whenever needed the central government would be asked for extra funding.
Lessons learned to date
The Fukushima Dai-ichi nuclear disaster revealed the dangers of building multiple nuclear reactor units close to one another. This proximity triggered the parallel, chain-reaction accidents that led to hydrogen explosions blowing the roofs off reactor buildings and water evaporating from open-air spent fuel pools—a situation that was potentially more dangerous than the loss of reactor cooling itself. Because of the proximity of the reactors, Plant Director Masao Yoshida "was put in the position of trying to cope simultaneously with core meltdowns at three reactors and exposed fuel pools at three units".
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- Dose limits in occupational radiation protection
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- TEPCO (Japanese) Handout 130828 07
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- Reuters (13 September 2013) Tritium levels reach new high at wrecked Fukushima nuclear plant
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- Total Tritium in contaminated water increasing by 330 [sic] Trillion Bq per year / Beyond discharge-able amount – Fukushima Diary
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- Based on archived video of the plant from TEPCO
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- MOFA Information on contaminated water leakage at TEPCO’s Fukushima Daiichi Nuclear Power Station, Ministry of Foreign Affairs
- TEPCO News Releases, Tokyo Electric Power Company
- NRA, Japan, Nuclear Regulation Authority
- NISA, Nuclear and Industrial Safety Agency, former organization
- Fukushima Diary News site of a concerned Japanese man in Europe