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Timeline of the discharge of radioactive materials of the Fukushima Daiichi nuclear disaster ja:福島第一原発事故による放射性物質の拡散

TEPCO responses /timeline
On 20 August2013, in a further incident, it was announced that 300 t of heavily contaminated water had leaked from a storage tank. The leak was assessed as Level 3 on the International Nuclear Event Scale.

On 26 August 2013, the Japanese government under Second Abe Cabinet took charge of emergency measures to prevent further radioactive water leaks, reflecting their lack of confidence in TEPCO.

History of understating radioactivity. For example, in 2014, TEPCO blamed its measuring method and revised the figures of strontium in a groundwater well in July 2013 to be 5 million becquerels per liter, which is 160,000 times the standard for discharge.


 * Underground barrier

In August 2013, the contaminated groundwater had breached an underground barrier, was rising toward the surface and exceeded legal limits of radioactive discharge. The underground barrier was only effective in solidifying the ground at least 1.8 meters below the surface, and water began seeping through shallow areas of earth into the sea.

On 31 March 2016, an underground ice wall (also known as "frozen soil barrier") built by TEPCO began operation. It was designed to prevent further contamination of seeping groundwater by melted-down nuclear fuel. However, in July 2016 TEPCO revealed that the ice wall had failed to stop groundwater from flowing in and mixing with highly radioactive water inside the wrecked reactor buildings, adding that "its ultimate goal has been to 'curtail' groundwater inflow, not halt it". By 2019, the ice wall had reduced the inflow of groundwater from 440 cubic meters per day in 2014 to 100 cubic meters per day, while contaminated water generation decreased from 540 cubic meters per day in 2014 to 170 cubic meters per day.

Contamination of US food
Migratory pelagic fish are highly effective and rapid transporters of radioactivity throughout the ocean. Elevated levels of caesium-134 appeared in migratory species off the coast of California that were not seen pre-Fukushima.
 * US govt claims "Higher concentration than before, but still safe"

In 2018, scientists discovered increased traces of radioactive isotope Caesium-137 in wine grown in a vineyard in Napa Valley, California. The trace-level radioactivity was in dust blown across the Pacific Ocean.

Transfer to other article
A monitoring system operated by the Preparatory Commission for the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) tracked the spread of radioactivity on a global scale. Radioactive isotopes were picked up by over 40 monitoring stations. On 12 March, radioactive releases first reached a CTBTO monitoring station in Takasaki, Japan, around 200 km away. The radioactive isotopes appeared in eastern Russia on 14 March and the west coast of the United States two days later. By day 15, traces of radioactivity were detectable all across the northern hemisphere. Within one month, radioactive particles were noted by CTBTO stations in the southern hemisphere.
 * Radiation effects from the Fukushima Daiichi nuclear disaster
 * paragraphs "Water releases", "Discharge to seawater and contaminated sealife"
 * Fukushima Daiichi nuclear disaster
 * paragraphs "Releases of radioactive contamination", "Contamination in the eastern Pacific"
 * monitoring (transfer to other article)


 * exposure to radition (transfer to other article)

In August 2012, researchers found that 10,000 nearby residents had been exposed to less than 1 millisievert of radiation, significantly less than Chernobyl residents. Estimates of radioactivity released ranged from 10–40%  of that of Chernobyl. The significantly contaminated area was 10 -12% of that of Chernobyl. In March 2011, Japanese officials announced that "radioactive iodine-131 exceeding safety limits for infants had been detected at 18 water-purification plants in Tokyo and five other prefectures". On 21 March, the first restrictions were placed on the distribution and consumption of contaminated items. , the Japanese government was unable to control the spread of radioactive material into the nation's food supply. Radioactive material was detected in food produced in 2011, including spinach, tea leaves, milk, fish, and beef, up to 320 kilometres from the plant. 2012 crops did not show signs of radioactivity contamination. Cabbage, rice and beef showed insignificant levels of radioactivity. A Fukushima-produced rice market in Tokyo was accepted by consumers as safe. In 2015, the tap water contamination was still higher in Tokyo compared to other cities in Japan.
 * comparison to chernobyl (transfer to other article)
 * Contamination of Japanese food



Statistical details
Results revealed on 22 March from a sample taken by TEPCO about 100 m south of the discharge channel of units 1–4 showed elevated levels of Cs-137, caesium-134 (Cs-134) and I-131. A sample of seawater taken on 22 March 330 m south of the discharge channel (30 kilometers off the coastline) had elevated levels of I-131 and Cs-137. Also, north of the plant elevated levels of these isotopes were found on 22 March (as well as Cs-134, tellurium-129 and tellurium-129m (Te-129m)), although the levels were lower. Samples taken on 23 and/or 24 March contained about 80 Bq/mL of iodine-131 (1850 times the statutory limit) and 26 Bq/mL and caesium-137, most likely caused by atmospheric deposition. By 26 and 27 March this level had decreased to 50 Bq/mL (11) iodine-131 and 7 Bq/mL (2.9) caesium-137 (80 times the limit). Above the seawater, IAEA reported "consistently low" dose rates of 0.04–0.1 μSv/h on 27 March.

By 29 March iodine-131 levels in seawater 330 m south of a key discharge outlet had reached 138 Bq/ml (3,355 times the legal limit), and by 30 March, iodine-131 concentrations had reached 180 Bq/ml at the same location near the Fukushima Daiichi nuclear plant, 4,385 times the legal limit. The high levels could be linked to a feared overflow of highly radioactive water that appeared to have leaked from the unit -2 turbine building. On 15 April, I-131 levels were 6,500 times the legal limits. On 16 April, TEPCO began dumping zeolite, a mineral "that absorbs radioactive substances, aiming to slow down contamination of the ocean."


 * Seawater radionuclide concentration on 29 March 2011:
 * {| class="wikitable" border="1"

! Nuclide ! Concentration (Bq/cm3) ! Regulatory limit (Bq/cm3) ! Concentration / Regulatory Limit
 * 0.16
 * 40
 * .0004
 * 130
 * 0.04
 * 3250
 * 31
 * 0.06
 * 517
 * 2.8
 * 0.3
 * 9.3
 * 32
 * 0.09
 * 356
 * 5.0
 * 0.3
 * 17
 * 2.5
 * 0.4
 * 6.3
 * }
 * 32
 * 0.09
 * 356
 * 5.0
 * 0.3
 * 17
 * 2.5
 * 0.4
 * 6.3
 * }
 * 2.5
 * 0.4
 * 6.3
 * }

Contaminated water

 * Treatment of contaminated water

Continued cooling of the melted reactor cores is required in order to remove excess heat. Due to damage to the integrity of the reactor vessels, radioactive water accumulates inside the reactor and turbine buildings. To decontaminate the contaminated water, TEPCO installed radioactive water treatment systems.

Management of contaminated water
The Japanese government had initially requested the assistance of the Russian floating water decontamination plant Landysh to process the radioactive water from the damaged reactors, but negotiations with the Russian government were an extremely slow process and it is unclear if the plant was ever sent to Fukushima. Landysh was built by Russia with funding from Japan to process liquid wastes produced during the decommissioning of nuclear submarines.

Installation of circulating water cooling system
In order to remove decay heat of the severe damaged cores of Unit 1–3, TEPCO injected cooling water into the reactors. As the reactors appear to have holes around the bottom, the water dissolved the water-soluble fission products, which then accumulated in the basement of the turbine building (the adjacent diagram #2) through any leaks from the water-injected reactor buildings (#1). Since the accumulated radioactive water was a risk, TEPCO tried to transfer it.

As the accumulated water in the basement (see the tunnel below diagram #2) of the turbine building of Units 2 and 3 was radioactive, TEPCO needed to remove it. They had initially planned to pump the water to the condenser (the large black vessel in diagram #1). TEPCO had to abandon that plan after discovering that the condensers on both units were already full of water. Pumps capable of processing 10–25 tons of water per hour were used to transfer condenser water into other storage tanks, freeing up condenser storage for the water in the basements. Since both the storage tanks and the condensers were nearly full, TEPCO also considered using floating tankers ships as a temporary storage location for the radioactive water.

At the same time, on 5 April, TEPCO began pumping water from the condensers of units 1–3 to their respective condensation storage tanks to free room for the trench water.



Removal of accumulated water in seawater piping trench
The Fukushima Daiichi NPS has several seawater piping trenches that were originally designed to house pipes and cables running from the Unit 2–4 turbine buildings to their seaside, which doesn't directly connect to the sea. Inside the trench, radioactive contaminated water has been accumulating since the accident. Due to the risk of soil or ocean contamination from these trenches, TEPCO has been trying to remove the accumulated water in the trenches by pumping it back into the turbine buildings, as well as backfilling the trenches to reduce or prevent further incursion of contaminated water.

Discovery of Groundwater contamination in July 2013
On 5 July 2013, TEPCO found 9 kBq/L of 134Cs and 18 kBq/L of 137Cs in a sample taken from a monitoring well close to the coastline. Compared with samples taken three days earlier, the levels were 90 times higher. The cause was unknown. The monitoring well is situated close to another monitoring well that had previously leaked radioactive water into the sea in April 2011. A sample of groundwater from another well situated about 100 meters south of the first well showed that the radioactivity had risen by 18 times over the course of 4 days, with 1.7 kBq/L of strontium and other radioactive substances. A day later the readings in the first well were 11 kBq/L of 134Cs and 22 kBq/L of 137Cs, 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 groundwater contamination was discovered, TEPCO started 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. TEPCO's solution resulted in redirection of the groundwater flows, which could have spread the radioactive contamination further. Besides that, TEPCO had plans for pumping groundwater. At that time the turbine buildings of units 2 and 3 contained 5000 and 6000 cubic meters of 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.

Timeline of contaminated water treatment
On 21 April 2011, TEPCO estimated that 520 tons of radioactive water leaked into the sea before leaks in a pit in unit 2 were plugged, totaling 4.7 PBq of water release (calculated by simple sum, which is inconsistent with the IAEA methodology for mixed-nuclide releases ) (20,000 times facility's annual limit). TEPCO's detailed estimates were 2.8 PBq of I-131, 0.94 PBq of Cs-134, 0.940 PBq of Cs-137. Measurements taken on 21 April indicated 186 Bq/l measured 34 km from the Fukushima plant.
 * 2011
 * On March 27
 * TEPCO announced that radioactive water had accumulated in the basement of the Unit 2 turbine building.
 * On March 28
 * The Japanese Nuclear Safety Commission advised TEPCO to take all possible measures to avoid the accumulated water in the Unit 2 turbine building leaking into the ground and the sea. (hereinafter called "the JNSC advice")
 * On April 2
 * TEPCO announced the outflow of fluid containing radioactive materials to the ocean from areas near the intake channel of Unit 2. The fluid source was a 20 cm crack on the concrete lateral of the pit that appeared to have been created by the earthquake. TEPCO attempted to inject fresh concrete, polymeric water absorbent, sawdust, and shredded newspapers into the crack; this approach failed to slow the leak. After an investigation of the water flow, TEPCO began to inject sodium silicate on April 5th, and the outflow was stopped on April 6th. The total amount and radioactivity of the outflow from the crack was estimated to be approximately 520 m3 and approximately 4.7 PBq respectively.
 * On April 17
 * TEPCO announced the Roadmap towards Restoration from the Accident at Fukushima Daiichi Nuclear Power Station.

In May 2011, another 300,000 tons of relatively less-radioactive water had already been reported to have leaked or been purposefully pumped into the sea to free room for storage of highly radioactively contaminated water. On 11 May 2011, TEPCO announced it believed it had sealed a leak from unit 3 to the sea; TEPCO did not immediately announce the amount of radioactivity released by the leak.

In addition to the large releases of contaminated water (520 tons and 4.7 PBq ) believed to have leaked from unit 2 from mid-March until early April, another release of radioactive water is believed to have contaminated the sea from unit 3, because on 16 May TEPCO announced seawater measurements of 200 Bq per cubic centimeter of caesium-134, 220 Bq per cubic centimeter of caesium-137, and unspecified high levels of iodine shortly after discovering a unit-3 leak.
 * On April 27
 * In order to prevent the outflow of the highly radioactive water at the turbine building of Unit 2, the water was transferred to the Centralized Radiation Waste Treatment Facility since April 19th. TEPCO planned to install facilities for processing the stored water and reusing treated water to inject it into the reactors.
 * On May 11
 * TEPCO investigated possible leakage of radioactive water to the outside from around the intake canal of Unit 3 in response to the employees' report of water flowing into the pit via power cable pipe lines.
 * On May 23
 * Nuclear and Industrial Safety Agency began to use the term "Contaminated Water" as the water with high concentration of radioactive materials.
 * On June 17
 * TEPCO began the operation of the cesium adsorption apparatus (Kurion) and the decontamination apparatus (AREVA).
 * On August 17
 * TEPCO began the (test) operation of SARRY, which is the second cesium adsorption apparatus (TOSHIBA).
 * On August 28
 * 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 December 21
 * TEPCO announced Mid-and-long-Term Roadmap towards the Decommissioning of Fukushima Daiichi Nuclear Power Units 1-4.


 * 2012
 * On April 5
 * A leaking pipe was found at 1.00 AM. 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.
 * On September 19
 * Nuclear Regulation Authority (NRA) was established.


 * 2013 (The year to the social problem)
 * On March 30
 * TEPCO began the operation of ALPS, which is the multi-nuclide removal equipment.
 * On July 22
 * With announcing the situation on seawater and groundwater, TEPCO admitted that contaminated groundwater had been leaking into the ocean since March 2011.
 * On July 27
 * TEPCO announced that extremely high levels of tritium and cesium were found in a pit containing about 5000 cubic meters water on the sea side of the Unit 2 reactor building. 8.7 MBq/liter of tritium and 2.35 GBq/liter of cesium was measured. 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. TEPCO believed that this pollution was there from the first days in 2011, and had stayed there. Nevertheless, TEPCO would control the site for leaks, and seal the soil around the pit.
 * On May 30
 * The Government of Japan decided the policy to prevent the groundwater flowing in the reactor buildings. A frozen soil wall (Land-side Impermeable Wall) was scheduled for introduction to block the flow of groundwater and prevent its mixing with contaminated water.
 * On August 19
 * Contaminated water leakage from a flange type tank was found in the H4 area. The incident was finally evaluated by the NRA as a provisional rating Level 3 on the eight-level INES. In response to this incident, NRA recommended that TEPCO should replace the flange type tank, which is prone to leak water, with a welded type tank.
 * On August 28
 * 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 from prior to decontamination were not released. The man was released, but ordered to have a whole-body radiation count later.
 * On September 2
 * It was reported that radiation near another tank was measured at 1.8 Sv/h, 18 times higher than previously thought. TEPCO had initially recorded radiation at about 100 mSv/h, 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.
 * On September 3
 * The Nuclear Emergency Response Headquarters published "the Government’s Decision on Addressing the Contaminated Water Issue at TEPCO’s Fukushima Daiichi NPS".
 * On September 9
 * 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.
 * On September 12
 * Contaminated water leakage from storage tanks was found in the H4 area.

On 10 September 2015, which floodwaters of Typhoon Etau overwhelmed the drainage pumps. TEPCO said that hundreds of metric tons of radioactive water entered the ocean as a result. Plastic bags filled with contaminated soil and grass were also swept away by the flood waters.