Fukushima nuclear accident cleanup

International experts have said that a workforce in the hundreds or even thousands would take years or decades to clean up Japan's Fukushima Daiichi nuclear disaster. On 10 April 2011, Tokyo Electric Power Company (TEPCO) began using remote-controlled, unmanned heavy equipment to remove debris from around nuclear reactors 1–4. TEPCO announced on 17 April that it expected to have the automated cooling systems restored in the damaged reactors in about three months and have the reactors put into cold shutdown status in six months. TEPCO plans 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.

When the monsoon season began in June, a light fabric cover was used to protect the damaged reactor buildings from storms and heavy rainfall. On 1 August 2011, TEPCO said that very high radiation levels were found outside the building of reactor 1 and 2 from an exhaust-pipe. On 16 August, TEPCO announced the installation of devices in the spent 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. Burying the reactors in sand and concrete is considered to be a last resort.

In October 2011, Japanese Prime Minister Yoshihiko Noda said the government will spend at least 1 trillion yen ($13 billion) to clean up vast areas contaminated by radiation from the Fukuahima nuclear disaster. Japan "faces the prospect of removing and disposing 29 million cubic meters of soil from a sprawling area in Fukushima, located 240 kilometers (150 miles) northeast of Tokyo, and four nearby prefectures".

Overview

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, says "they are improvising with tools that were not intended for this type of situation". However, on 17 April, TEPCO appeared to put forward the broad basis of a plan which includes: (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.

Critics were "not fully convinced TEPCO could meet the timetable it has set for itself to achieve a cold shutdown" because the "scale and complexity of the challenge is unprecedented". Long term plans for Units 5 and 6 have not been announced, "but they too may need to be decommissioned".

On 5 May, 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.

The disaster in Fukushima has revealed the practice of Japanese nuclear powerplants of 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 could be concluded that 80 percent of all workforce in commercial nuclear powerplants is employed on temporary contracts, In Fukushima this number was even 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 powerplants. They would get a contract for a few months to do unskilled and the most dangerous labor. No protection in case of an accident, and no insurance against diseases as leukemia and other forms of cancer they could endure in the long run. After the work was finished, these people were supposed to disappear.

Scope of cleanup

International experts have said that a workforce in the hundreds or even thousands would take years or decades to clean up the area. John Price, a former member of the Safety Policy Unit at the UK's National Nuclear Corporation, has said that it "might be 100 years before melting fuel rods can be safely removed from Japan's Fukushima nuclear plant". Edward Morse, a professor of nuclear engineering at the University of California, Berkeley, has said:

... there would be at least six months of emergency stabilisation, about two years of temporary remediation and up to 30 years of full-scale clean-up. Furthermore, the high levels of ground contamination at the site are raising concerns about the viability of individuals to work at the site in coming decades.

However, according to BBC News, 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, it took 11 years after the accident before the vessel of the partially melted core was first opened, with cleanup activities taking several more years.

TEPCO announced on 17 April 2011 that it expected to have the automated cooling systems restored in the damaged reactors in about three months and have the reactors put into cold shutdown status in six months.

In October 2011, Japanese Prime Minister Yoshihiko Noda said the government will spend at least 1 trillion yen ($13 billion) to clean up vast areas contaminated by radiation from the Fukuahima nuclear disaster. Japan "faces the prospect of removing and disposing 29 million cubic meters of soil from a sprawling area in Fukushima, located 240 kilometers (150 miles) northeast of Tokyo, and four nearby prefectures".

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.

Water treatment

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 interrupt the vicious cycle of injecting water into reactors to cool them and ending up with more contaminated water.

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, 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 hopes 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 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. Tepco announced that yet another system, named SARRY 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. This Sarry-system 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 of the were put into actual operation on Sunday 7 August, after the testing was completed. Six more additional units were planned to be operational 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 whit a leaking valve that did not close. It was found that they were exposed to 0.16 and .14 millisievelts. 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.

Radioactive Waste

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.

Water in the basement

Side view of the Fukushima trenches and tunnels. 1: Reactor building, 2: Turbine generator and associated condenser.

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

Construction of internationally-compatible emergency pump valves for Fukushima complex, Yokota AB

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

Leakage route of highly radioactive water through a gravel layer.
1: Reactor building, 2: Turbine building, 3: Injection of sodium silicate.

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.

Ongoing efforts

With the leak plugged, at least temporarily, on 10 April 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.

On 19 April, TEPCO estimated that the Unit 2 turbine basement contained 25,000 cubic meters of contaminated water, it would later estimate this water contained 400 PBq of radioactivity.

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 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 enter through cracks in walls into the basements of the reactor-buildings. TEPCO calculated that this could be some 200 to 500 tons on a daily basis. This would increase the amount of high 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.

Spent fuel pools

On August 16 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.

Debris removal

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.

Hotspots

On 1 August 2011, TEPCO admitted that very high radiation-levels were found outside the building of reactor 1 and 2 from an exhaust-pipe. Up to 10,000 mSv/h and probably more because the maximum reading of these devices was 10,000 mSv/h. According to experts an exposure of 15 minutes in such an environment would be lethal. On 2 August TEPCO revealed that in a room on the second floor of reactor 1 levels of radioactivity up to 5,000 mSv/h were measured, the highest levels at the facility since the March accident.

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. The cost of building structures around Units 1 – 4 and wrapping them with the sheets is estimated to reach 80 billion yen (roughly equivalent to 1 billion U.S. dollars). On 6 April, 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.

Proposed building protections

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.

Sarcophagus

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,

New filters

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.

Cleanup of neighboring areas

Significant efforts are being taken to cleanup 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 designeated 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 2 years radiation levels between 5-20 millisieverts should be cut down to 60%.
• the Japanese government would help local authorities with disposing the enormous amount of radioactive waste.