Severity of radioactive water tank leak at Fukushima plant upgraded to Level 3
The Nuclear Regulation Authority (NRA) announced Aug. 21 that the leakage of water containing highly concentrated radioactive substances from an above-ground tank at the Fukushima No. 1 nuclear plant is consistent with a Level 3 (serious incident) on the International Nuclear and Radiological Event Scale (INES).
Because the evaluation criteria is not normally used for incidents occurring in conjunction with the cleanup process following a nuclear accident, however, the matter is being referred to the International Atomic Energy Agency (IAEA) for a final determination on whether or not the appraisal is appropriate.
After initially determining a provisional rating of Level 1 (anomaly) for the incident, the NRA decided to reevaluate the matter after learning that TEPCO had estimated the amount of leaked water from the plant to be around 300 metric tons — and the total radioactive release to be around 24 trillion becquerels, based on the density of radioactive substances found in the water.
Converting the figure to the INES criteria resulted in a rating of several thousand terabecquerels (tera=one trillion) — thereby leading to the final decision to assess the leak as a Level 3 incident.
The INES is an internationally recognized tool developed by organizations including the IAEA to measure the scale and seriousness of nuclear-related problems such as nuclear power accidents. Depending on the amount of radiation released and the effects both on- and off-site, the scale is classified into eight levels ranging from 0 (too low to be rated) to 7 (major accident). The 2011 accident at the Fukushima plant and the 1986 Chernobyl disaster were both classified as Level 7.
The INES criteria are based on the assumption of accidents occurring at facilities deemed to be structurally sound, however, prompting an objection from NRA Commissioner Toyoshi Fuketa.
“I have doubts about appraising this situation based on simple calculations,” he commented. “I think we should consider whether there is any meaning to assessing a Level 3 incident on top of an accident that has already been classified as a Level 7.”
“We have no time to lose with respect to the situation that is now occurring,” countered NRA Chairman Shunichi Tanaka, announcing that the matter would indeed be referred to the IAEA.
The NRA will ask the IAEA to determine whether or not it is appropriate to make an assessment with respect to problems that occurred during cleanup-related emergency measures. The IAEA will also be asked to clarify whether radioactive materials released during the initial accident should be subsumed within the category of the accident itself when released a second time in the form of contaminated water.
If the level upgrade is approved, it will be the first time that any such rating has been given since the Fukushima plant accident itself was raised to a level 7 in April 2011.
The leak was discovered coming from one of the prefab storage tanks on-site, each of which is 11 meters tall, 12 meters in diameter, and able to hold 1,000 tons of water. The steel tanks are about 500 meters west of the ocean.
Measurements of the contaminated water revealed a ratio of 80 million becquerels of radioactive substances per liter. While leaks from the tanks had been found on four previous occasions, the present leak is the largest to date, and is on the same scale as the contaminated groundwater leak into the ocean revealed on July 22.
Three hundred and fifty tanks of the same type were hurriedly erected following the earlier leaks. The tanks contain water that became contaminated with radioactive cesium after being used to cool the nuclear reactors. The water was due to be stored temporarily in the tanks, and then transported in order to undergo purification treatment designed to remove 62 types of radioactive substances.
The leaky tank is located in a section that includes 25 other tanks. The area had been surrounded by a double-layered barrier made of concrete and sandbags in order to prevent seepage, but it was discovered that the contaminated water had escaped through the sandbags.
The radiation dose inside the barrier was measured at 100 millisieverts per hour, or 100 times greater than the average yearly exposure for the general population. A high level of radiation was also detected outside the sandbag barrier, at more than 90 millisieverts per hour.
The level of radioactive substances inside a drainage canal that connects directly to the ocean, some 20 meters away from the tank, was found to be a low 130 becquerels per liter, however — leading TEPCO to comment that “no spillage into the ocean has been detected so far.”
TEPCO is now working to determine the exact locations of the leaks.
Mainichi Shimbun, August 21, 2013
http://mainichi.jp/english/english/newsselect/news/20130821p2a00m0na018000c.html
Radioactive water leak from tank at Fukushima No. 1 may have reached sea: Tepco
Several hundred tons of radioactive water that leaked from a storage tank at Tokyo Electric Power Co.’s crippled Fukushima No. 1 nuclear plant may have flowed to the sea, Tepco admitted Wednesday, adding that it is “hurriedly checkin” to learn if 350 similar tanks are also leaking.
Tepco is desperately trying to seal the tank, which has leaked about 300 tons of radioactive water. The tank, considered temporary, is made of steel plates bolted together with sealed seams. Tepco is also using more durable welded tanks to store the highly radioactive water, which is accumulating daily.
The water was used to cool the three melted reactors, then stored for later possible decontamination. So far, Tepco has built more than 1,000 tanks on site.
Spokesman Tsuyoshi Numajiri said traces of radioactivity were detected in a drainage stream.
“There is a possibility that earth and sand contaminated with the leaked water flowed into the drainage. We cannot rule out the possibility that part of the contaminated water flowed into the sea,” he said.
“We intend to make detailed examinations.”
A Tepco official said earlier Wednesday the tank was believed to still be leaking but the utility has yet to pinpoint where the hole is. The water is apparently being absorbed into the ground and possibly mixing with the groundwater that flows under the stricken plant.
Tepco was also desperately trying to determine if 350 similar temporary tanks at the plant were also leaking.
Numajiri said workers are removing soil contaminated by the leaked water, and pumping the remaining water from the leaky tank.
He said there were no significant changes in radiation levels outside the plant.
AFP-Jiji Press, August 21, 2013
http://www.japantimes.co.jp/news/2013/08/21/national/radioactive-water-leak-from-tank-at-fukushima-no-1-may-have-reached-sea-tepco/#.Uhq5xH9jbRZ
Rate of radioactive flow to Pacific alarming — Fukushima No. 1 leaks estimated at 30 trillion becquerels since May 2011
Water releasing as much as 10 trillion becquerels of radioactive strontium and 20 trillion becquerels of cesium-137 from the Fukushima No. 1 power plant has flowed into the Pacific Ocean since May 2011, Tokyo Electric Power Co. estimates.
The combined figure of 30 trillion becquerels, announced late Wednesday, implies that highly radioactive water is entering the trenches under the damaged reactors’ turbine buildings.
The three reactors that had core meltdowns are being flooded by emergency cooling water needed to keep the leaky units stable, but the water is leaking from the reactors into the basements, where it is mixing with groundwater penetrating the walls of the 40-year-old plant.
Since the 30 trillion becquerels can’t be accounted for just by groundwater alone, it is likely the toxic water from the trenches is entering the mix as well, the beleaguered utility said after conducting various simulations.
The Fukushima complex was built on a maze of trenches that guide cables and pipes needed to transport electricity and water. The pipes lead to the sea because the power plant, like all the others in Japan, needs seawater for cooling purposes.
The 30 trillion figure is about 100 times more than what Tepco had been allowing to enter the sea each year before the crisis.
Containment fences set up in the plant’s man-made harbor are failing to keep the flow from reaching the greater Pacific.
Tepco belatedly acknowledged last month that about 300 tons of groundwater from the mountains behind the crippled plant flows daily to the sea after mixing with radioactive water leaking from the reactor buildings’ cracked foundations.
This week, however, it discovered that about 300 tons of filtered water from one of its hundreds of temporary storage tanks had escaped. The water had been cleansed of most of the cesium but still contains other harmful materials, including tritium. The incident has been rated level 3 on the International Nuclear Event Scale. The meltdowns were rated level 7, a status that remains unchanged.
Tepco first claimed the tank water had not reached the sea, only to reverse itself Wednesday after detecting a relatively high reading of 6 millisieverts per hour in a drainage channel running from the tanks to the sea. The channel, made to prevent rainwater from flooding the tank premises, is not covered.
Tepco said Thursday that two more tanks are leaking.
On Monday, when Tepco announced the first tank leak, it confirmed seeing traces of water running from the tank to the drainage channel, and detected 96 millisieverts per hour of radiation in the air near it.
Tepco has been unable to locate the leak but said it finished transferring the water to other tanks nearby Wednesday night. It plans to check for more tank leaks.
While some of the water might have gone into the sea, it is hard to determine where it all went. Tepco projects that it’s been losing about 10 tons a day for the past 30 days from the tank, which is considered a temporary model as it is made of steel sheets bolted together with their seams sealed, instead of the more reliable welded tanks.
The leak was discovered after workers noticed water puddles near the tank Monday. Nuclear Regulation Authority officials and outside experts said Wednesday that if 10 tons of tainted water flowed out over 30 days, it is hard to imagine no one would notice it before Monday.
At an NRA meeting Wednesday evening on the tainted water issue, the panelists pointed out a long-held suspicion: that the water may be going into the ground through cracks in the concrete base.
“It is more natural to think the water went underground,” said Masaya Yasuhara, a researcher at the National Institute of Advanced Industrial Science and Technology. Tepco rejects that scenario because concrete isnÅft that permeable.
Kazuaki Nagata, Japan Times Staff Writer, August 22, 2013
http://www.japantimes.co.jp/news/2013/08/22/national/rate-of-radioactive-flow-to-pacific-alarming/#.Uhq_sH9jbRY
High-level radiation detected along seams of two Fukushima water tanks
Tokyo Electric Power Co. said Thursday it has detected high levels of radiation along the seams of two temporary storage tanks containing contaminated water at its crippled Fukushima No. 1 nuclear power station.
The seams on the bottom of the 1,000-ton tanks were dry, and no water was found near them, Tepco said.
Radiation levels of up to 100 millisieverts per hour were measured at each of the two tanks in question, according to the utility.
The cause of the high-level radiation along the seams of the two tanks remains unclear and the possibility of leaks cannot be ruled out, Tepco said.
The two tanks are the same type as the one that has leaked an estimated 300 tons of contaminated water at the plant, which suffered three reactor core meltdowns after the March 2011 mega-quake and tsunami. The leaking tank was discovered Sunday.
There are some 350 such tanks at the plant and about 300 are being used to temporarily store highly radioactive water. On Thursday, Tepco checked all 300 tanks. They are made of steel plates bolted together, with sealed seams. Tepco is also using more durable welded steel tanks.
Jiji Press, August 22, 2013
http://www.japantimes.co.jp/news/2013/08/22/national/high-level-radiation-detected-along-seams-of-two-fukushima-water-tanks/#.UhrGLX9jbRY
Toxic puddles found near water tanks at Fukushima plant
Puddles of water with extremely high radiation levels have been found near water storage tanks on the premises of the crippled Fukushima No. 1 nuclear power plant, nuclear regulators and plant operator Tokyo Electric Power Co. said Monday.
The radiation level, measured around 50 cm above the toxic water, stood at about 100 millisieverts per hour, Tepco said, while acknowledging that the water likely came from the tanks. It is possible that around 120 liters of water has so far leaked out.
Tepco denied that toxic water had flowed into the Pacific Ocean, but the Nuclear Regulation Authority ordered the utility to study the possibility that the toxic water had escaped into the sea through nearby drains.
The NRA released a preliminary assessment of a level 1 incident on an eight-point international scale, defined as an Åganomaly.Åh
A low barrier around the tanks is meant to block water from escaping when a leak occurs, but drain valves attached to the barrier may have been left open, allowing water to flow outside the barrier.
Kyodo News, August 20, 2013
http://www.japantimes.co.jp/news/2013/08/20/national/toxic-puddles-found-near-water-tanks-at-fukushima-plant/#.UhP_i39jbRY
300 tons of highly toxic water leaks from tank at Fukushima plant
TOKYO, Japan (Kyodo) — An estimated 300 tons of highly radioactive water has leaked from one of the water storage tanks at the crippled Fukushima Daiichi power plant, making it the worst leakage incident from such containers, plant operator Tokyo Electric Power Co. said Tuesday.
TEPCO detected in the leaked water 80 million becquerels per liter of radioactive substances emitting beta rays, such as strontium-90, and admitted that it has not yet identified from which area of the tank the polluted water is escaping.
“We think the leakage is continuing,” TEPCO spokesman Masayuki Ono told a press conference, but denied that toxic water is flowing into the adjacent Pacific Ocean on the grounds that the radiation level of the water in a nearby gutter was not high.
TEPCO calculated the amount of leakage based on the water level within the tank, which was about 2.9 meters lower than it should have been. The tank originally contained about 1,000 tons of contaminated water.
TEPCO has collected around 4 tons of the leaked water. Admitting that the toxic water has most likely flowed into the soil, TEPCO said it is currently working to prevent the spread of contamination.
The latest revelation came a day after TEPCO said puddles with extremely high radiation levels had been found near the tanks.
A massive volume of radioactive water has been accumulating at the Fukushima plant as a result of continuing water injections into the Nos. 1 to 3 reactors that suffered meltdowns during the nuclear crisis triggered by a huge earthquake and tsunami on March 11, 2011.
Kyodo News, August 20, 2013
http://mainichi.jp/english/english/newsselect/news/20130820p2g00m0dm038000c.html
Tepco testing tainted earth at No. 1 plant — Utility begins digging ground to assess extent of contamination
FUKUSHIMA — Tokyo Electric Power Co. on Friday started digging up soil tainted with highly radioactive water discharged from a storage tank at its Fukushima No. 1 nuclear plant to test its radiation levels.
The utility will dig areas measuring 12 sq. meters in total to a depth of 40 to 50 cm where pools of leaked radioactive water formed, and then measure levels to determine how far the contamination has spread and how much soil needs to be removed.
Some 300 tons of highly radioactive water recently spewed into the Pacific from one of 26 tanks built in an area just 500 meters from the plantÅfs seawall. The tanks are surrounded by dikes, but some 120 liters of the water leaked outside of them, making it necessary to collect soil to prevent the contamination from spreading.
Meanwhile, a 15-member team from the Nuclear Regulation Authority visited the Fukushima No. 1 complex Friday to check the storage tank from which the 300 tons of water is thought to have escaped.
The tank may not be the only source of leaked water, as Tepco said Thursday that it had detected high radiation levels around the bottom of two more tanks of the same design, an indicator that water may have leaked from those containers as well.
The nuclear watchdog’s team began the inspection Friday morning, an NRA official said.
Tepco has said puddles of water near the leaking tank were so toxic that anyone exposed to them would receive the same amount of radiation in an hour that a nuclear plant worker in Japan is allowed to receive in five years – 100 millisieverts.
Groundwater that mixed with the tainted water has already flowed to the ocean, and Tepco said Friday it has launched an operation to pump it out of 28 wells.
Jiji Press, Kyodo News, AFP-Jiji Press, August 23, 2013
http://www.japantimes.co.jp/news/2013/08/23/national/tepco-testing-tainted-earth-at-no-1-plant/#.UhrNhH9jbRY