The search for TEPCO's missing reactor fuel at Fukushima Daiichi has not proceeded smoothly as the fuel remains missing and the robotic probes continue to expire at an alarming rate.
The Mainichi describes the challenges to robotic investigation and the relative success of human investigative means, ar great biological cost (which remains undisclosed and unremarked).
In the first article, the Mainichi describes problems encountered by the robot operating in reactor 2, which encountered dents in the containment vessel while boring through it to insert a robotic camera.
Apparently, TEPCO is working from original architectural documents (a.k.a., "blue prints") that were not updated across the years, which has led to some unexpected challenges, such as the "dents" described in the article below:
Search for melted nuclear fuel at Fukushima plant's No. 2 reactor faces obstacles. The Mainchi, February 27, 2017 (Mainichi Japan) http://mainichi.jp/english/articles/20170227/p2a/00m/0na/011000cIn addition to encountering structural barriers, the robots are expiring rapidly due to high radiation levels. Humans have been forced to pick up where the robots fail:
Heavy machinery giant IHI Corp.'s Keizo Imahori, 38, who oversaw the mechanical boring of the containment vessel in December 2016, explains that, "A number of unexpected dents were found on the floor of the nuclear reactor building." This was a surprising discovery for Imahori and his team. The presence of the dents meant that it would be difficult for machines to get sufficiently close to the necessary areas to drill a hole, which in turn has a detrimental effect on the entire search for melted nuclear fuel.
As an emergency measure, 1-meter by 1-meter iron sheets were used to cover the dents, but workers involved in laying the sheets were exposed to extra radiation because of this additional work.
In addition to the dents, the No. 1 to No. 3 reactors at the Fukushima plant, which first started operating in the 1970s, had many parts that have undergone repair work not reflected in their original construction plans. It was impossible to check such changes in the structure beforehand due to high levels of radiation.
There was another problem -- the machines could not be attached to the side of the containment vessel, which meant workers were unable to carry out drilling work. This was caused by the containment vessel's paint peeling away. The problem was solved after workers peeled off the paint by hand, but this also caused them to be exposed to more radiation.
Robots' limitations exposed in search for melted nuclear fuel in Fukushima. The Mainichi, February 27, 2017 http://mainichi.jp/english/articles/20170227/p2a/00m/0na/016000cThis article notes that there are several meters of water under the containment vessels in reactors 1 and 3, which means the basements are flooded. That means any fuel in the basement is directly contaminating water that is flowing into the basements at a reported rate of 300 to 400 tons a day.
In the end, images from directly underneath the nuclear reactor were obtained not from the robot, but by "human means," on Jan. 30. By using a pipe and a camera, the team was able to confirm the presence of holes in the platform. They also discovered brown and black deposited material, which appeared to be melted nuclear fuel. Therefore, some might say that "human methods" are more effective than robots in a mission of this nature.
According to TEPCO, "This was the first probe of its kind in the world. We were able to collect sufficient data." However, critics would argue that six years have passed since the outbreak of the Fukushima nuclear disaster in 2011, and yet the exact situation regarding melted nuclear fuel at the site is still unclear.
Looking ahead, further difficulties are anticipated at both the No. 1 and No. 3 reactors, where in the past, there have been hydrogen explosions. This is mainly because there are several meters of contaminated water underneath the containment vessels, and the radiation levels are stronger than at the No. 2 reactor.
Here is an excerpt from my book Crisis Communication, Liberal Democracy and Ecological Sustainability published in 2016 by Lexington Press on Fukushima's radioactive water problem:
Fukushima’s Radioactive Water Problem
Fukushima’s radioactive water problem is unprecedented. TEPCO requires an endless stream of workers to manage contaminated water, which presents significant long-term challenges in addition to those posed by removing melted fuel from damaged reactors and spent fuel pools:
The situation, however, remains very complex, with the increasing amount of contaminated water posing a short-term challenge that must be resolved in a sustainable manner. The need to remove highly radioactive spent fuel, including damaged fuel and fuel debris, from the reactors that suffered meltdowns poses a huge long-term challenge.[i]
Contaminated water production at the Daiichi site poses long-term risks to the Pacific eco-system.
Damage by the March 11, 2011 earthquake, tsunami, and explosions problematized delivery of cooling water to melted fuel in reactors and spent fuel pools.
The plant manager resorted to using ocean water to cool melted fuel, a course of action that TEPCO officials had decided against, but was deployed as a desperate measure to halt uncontained nuclear fission in reactors and spent fuel pools.
Water used to cool fuel could not be recaptured, resulting in highly radioactive water contaminating the aquifer and Pacific Ocean.
Fukushima’s plant manager, Masao Yoshida, estimated that the level of radioactivity in the water flowing directly into the sea during the early days of the disaster exceeded 1,000 millisieverts.[ii]
Kyodo news reported on March 26, 2011 that “Levels of radioactive materials soaring in sea near nuke plant” citing data provided by Japan’s Nuclear and Industrial Safety Agency that found radioactive Iodine-131 in seawater sampled 300 meters south of plant, at a concentration 1,250.8 times the legal limit.[iii]
Dr. Ken Buesseler of Woods Hole Oceanographic Institution in Massachusetts measured levels of radioactive cesium in the ocean off of Fukushima at 100,000 Becquerels per cubic meter in early April of 2011.[iv] Buesseler reported in a 2013 presentation at MIT that prior to Fukushima, the Pacific Ocean measured ½ to 2 Becquerels per liter of cesium.[v]
The French Institute for Radiological Protection and Nuclear Safety (IRSN) declared Fukushima as the world’s worst nuclear contamination event ever for the ocean, reporting that from 21 March to 27 July, 27.1 petaBecquerels of Cesium-137 contaminated the ocean.[vi] Remember that one petaBecquerel is equivalent to a million billion Becquerels, or 10^15.[vii]
Cesium, among other radionuclides, is water-soluble and was likely transported across the Pacific Ocean by the Kuroshio Current,[viii] a fast moving current that every second carries approximately 50 million tons of sea water past Japan’s southeast coast.[ix] Relatively few figures are available for radioisotope contamination other than cesium.
A study of Iodine-129 levels in samples collected in June 2011 from the Western Pacific Ocean measured almost three orders of magnitude higher than pre-Fukushima background levels.[x]
A separate study published in Environmental Science Technology in 2012 reported that radiostrontium levels in surface seawater persisted through 2011 and were in some areas comparable, to or even higher, than those measured for Cesium-137 in December of 2011.[xi]
TEPCO has tried a variety of approaches to containing the contaminated water. During the summer of 2011, TEPCO installed concrete panels designed to seal water intakes of units 1 through 4 in order to prevent contaminated water from reaching the ocean.
In October 2011, TEPCO installed a steel water shield wall between the units and the ocean. TEPCO subsequently created a groundwater bypass system to reroute fresh water from flowing into the site and restored and improved its drainage system.
TEPCO has also worked on creating an ice wall that would prevent highly contaminated water in the basement of the wrecked reactors from flowing into the sea.[xii] All of these efforts have failed to prevent ongoing contamination of the Pacific Ocean.
In 2013, Prime Minister Abe promised the government would take “firm measures” to address water contamination at Fukushima Daiichi.[xiii] Yet, two years later in 2015, TEPCO still injects hundreds of tons of water into demolished reactor buildings 1-4 to cool uncontained melted fuel.[xiv]
TEPCO simultaneously pumps hundreds of tons of contaminated water out from the ruined reactor buildings, but its efforts to keep up with water saturation have been stymied by the sheer volume of ground water inundating the site, largely from an underground river running at about 1,000 tons daily, with TEPCO announcing that approximately 400 tons of that penetrates reactor buildings 1 – 4. [xv]
Water saturation from the underground river and TEPCO’s injections contribute to ground liquefaction, which poses direct risks to the reactor buildings and common spent fuel pool. Contaminated ground water is also flowing into the ocean.[xvi]
In February of 2015, TEPCO admitted that radioactive water from unit 2 had been flowing unfiltered into the ocean since May 2014.[xvii] Local fisherman who had given consent for TEPCO to dump uncontaminated ground water were outraged, but Yuji Moriyama, a TEPCO spokesman stated “the utility did not disclose the information because there is no evidence of environmental impact.”
The water contained 29,400 Becquerels of radioactive cesium per liter and an additional 52,000 Becquerels of beta-emitting radionuclides, such as Strontium-90.
Strontium levels in sea and ground water may actually rise over time, if the conditions modeled in two German risk studies apply to Fukushima.
The “German Risk Study, Phase B” found that a core meltdown accident could result in complete failures of all structural containment, causing melted fuel to exit the reactor foundation within five days and that ground water leaching would occur even in the absence of a full melt-through situation.[xviii]
A second German risk analysis, “Dispersion of Radionuclides and Radiation Exposure after Leaching by Groundwater of a Solidified Core-Concrete Melt,” found that even in the event of an intact building foundation, passing groundwater would be in direct contact with fuel, causing leaching of fission products. [xix]
The study predicted concentrations of Strontium-90 in river water would spike relatively suddenly, but maintain extraordinarily high levels of contamination for years, with “the highest radionuclide concentration of approx. 1010 Bq/m3 is reached by Sr-90 after some 5000 days.”
The study’s experimental conditions are roughly similar to Daiichi’s site conditions, including groundwater emptying into an adjacent river, whereas Daiichi is physically situated above an underground river emptying into the sea.
Ground water contamination has also been rising steadily at the Daiichi site, especially since the summer of 2013.[xx] TEPCO reported that samples from the well between the ocean and unit 1 measuring a record 5 million Becquerels per liter of radioactive Strontium-90 alone in July 2013.[xxi]
In January 27, 2015, TEPCO measured 31,000,000 Bq/m3 of Strontium-90 in boring well nearest unit 2, a level which was more than 10 percent more than reported in December of 2014.[xxii] By February of 2015, TEPCO was reporting even higher levels of Strontium-90 in the same location, with the highest sample measured at 590,000,000 Bq/m3 of Strontium-90.[xxiii]
The spiking strontium levels are consistent with the predictions of the German melt-through scenario.
TEPCO has also detected increased radionuclide contamination in the Fukushima port. On June 19, 2015 TEPCO’s reported that it had detected Strontium-90 measuring 1,000,000 Bq/m3 in two locations in Fukushima Daiichi’s port located near the water intake for reactors 3 and 4, exceeding the previous reported high of 700,000 Bq/m3.[xxiv]
The highest Strontium level measured in Fukushima’s port jumped still more in data reported in July 17, 2015 to 1,500,000 Bq/m3.[xxv]
TEPCO is also facing severe problems filtering and storing the contaminated water it does pump out from the ground and ruined buildings. In May of 2013 The Asahi Shimbun reported the TEPCO was going to begin dumping groundwater at the Daiichi site because its storage capacities for contaminated water were nearly exhausted. [xxvi]
There was considerable resistance from local fisherman because TEPCO lacked the capacity to remove Strontium-90 from captured water and even the filtered water was quite contaminated. At that time in 2013, filtered water measured 710 million Becquerels per liter while unfiltered water was reported as twice as radioactive, from tritium and strontium. TEPCO was not able to eliminate Strontium until the fall of 2014.[xxvii]
In 2015 the NRA approved a plan to allow TEPCO to dump decontaminated groundwater into the sea if the water registered less than 1 Becquerel per liter of cesium, less than 3 Becquerels per liter of beta emitters such as Strontium-90, and 1,500 Becquerels per liter of tritium.[xxviii]
TEPCO has attempted to store as much water as possible but press releases and news coverage addressing water storage at the plant suggest that official announcements of dumped water are the tip of a larger deluge....
[i] IAEA Team Completed Third Review of Japan's Plans to Decommission Fukushima Daiichi,” IAEA (February 17, 2015), https://www.iaea.org/newscenter/pressreleases/iaea-team-completed-third-review-japans-plans-decommission-fukushima.
[ii] T. Sugimoto and H. Kimura (1 December 2012) ‘TEPCO Failed to Respond to Dire Warning of Radioactive Water Leaks at Fukushima’, The Asahi Shimbun, http://ajw.asahi.com/article/0311disaster/fukushima/AJ201212010037, date accessed 2 December 2012.
[iii] “Levels of radioactive materials soaring in sea near nuke plant” Kyodo (March 26, 2011). http://english.kyodonews.jp/news/2011/03/81163.html
[iv] Cited in H. Tabuchi (25 June 2012) ‘Fears Accompany Fishermen in Japanese Disaster Region’, The New York Times, http://www.nytimes.com/2012/06/26/world/asia/fears-accompany-fishermen-in-japanese-disaster-region.html?nl=todaysheadlines&emc=edit_th_20120626, date accessed 26 June 2012.
[v] Buesseler, K. (2013, October 24). Japan’s continuing nuclear nightmare: Experts discuss Fukushima and its aftereffects. Massachusetts Institute of Technology Center for International Studies. Available http://techtv.mit.edu/collections/mit-cis/videos/26614-japan-s-continuing-nuclear-nightmare.
[vi] ‘Fukushima Nuclear Pollution in Sea was World's Worst: French Institute’ (28 October 2011), Japan Today, http://www.japantoday.com/category/national/view/fukushima-nuclear-pollution-in-sea-was-worlds-worst-french-institute, date accessed 29 October 2011.
[vii] ‘Fukushima Disaster Produces World’s Worst Nuclear Sea Pollution’, (28 October 2011), The Maritime Executive, http://www.maritime-executive.com/article/fukushima-disaster-produces-world-s-worst-nuclear-sea-pollution, date accessed 29 October 2011.
[viii] Pascal Bailly Du Bois, Pierre Garreau, Philippe Laguionie, Irene Korsakissok (2014) Comparison between modelling and measurement of marine dispersion, environmental half-time and 137Cs inventories after the Fukushima Daiichi accident. Ocean Dynamics, 64(3), 361.
[ix] R. A. Barkley, The Kuroshio Current,” Science Journal (March 1970), 54-60, http://swfsc.noaa.gov/publications/CR/1973/7302.PDF.
[x] S. Tumey, T. Guilderson, T. Brown, T. Broek, K. Buesseler, “Input of Iodine-129 into the western pacific ocean resulting from the Fukushima Nuclear Event,” Journal of Radioanalytical and Nuclear Chemistry, 296 (2013): 957–962. 10.1007/s10967-012-2217-9
[xi] P. Povinec, K. Hirose, and M. Aoyama (18 September 2012) ‘Radiostrontium in the Western North Pacific: Characteristics, Behavior, and the Fukushima Impact’, Environmental Science & Technology, 46.18, 10356–10363.
[xii] Nuclear Energy Institute. What is the status of radioactive water treatment at the site? (no date) http://www.nei.org/Issues-Policy/Safety-Security/Fukushima-Recovery/Radioactive-Water.
[xiii] Mari Yamaguchi AP “Japanese government to help halt nuke leak,” The Spokesman (August 8, 2013). Retrieved 4 May 2014: http://www.spokesman.com/stories/2013/aug/08/japanese-government-to-help-halt-nuke-leak/.
[xiv] R. Yoshida (21 May 2013) ‘Fukushima No. 1 Can’t Keep its Head above Tainted Water’, Japan Times, http://www.japantimes.co.jp/news/2013/05/21/reference/fukushima-no-1-cant-keep-its-head-above-tainted-water/#.UZpke8oQNX9, date accessed 21 May 2013.
[xv] Nagata, K. (2013, August 20). TEPCO yet to track groundwater paths. Liquefaction threat adds to Fukushima ills. The Japan Times. Available http://www.japantimes.co.jp/news/2013/08/20/national/tepco-yet-to-track-groundwater-paths/#.U2XHpF7K3yi
[xvi] Nagata, K. (2014, March 6). Solving Fukushima water problem a long, hard slog. The Japan Times. Available http://www.japantimes.co.jp/news/2014/03/06/national/solving-fukushima-water-problem-a-long-hard-slog/#.U2XIE17K3yh
[xvii] Fisheries ‘shocked’ at silence over water leak at wrecked Fukushima No. 1 plant,” Japan times (February 25, 2015) http://www.japantimes.co.jp/news/2015/02/25/national/tepco-admits-failed-disclose-cesium-tainted-water-leaks-since-april/#.VPOfiOHWyDl
[xviii] Gesellschaft fur Reaktorsicherheit (GRS) Deutsche Risikikostudie Kernkraftwerke, Phase B Report GRS-89 cited in Bayer, A., Al-Omari, I., & Tromm, W. (1989). Dispersion of radionuclides and radiation exposure after leaching by groundwater of a solidified core-concrete (No. KFK-4512). Available http://www.irpa.net/irpa8/cdrom/VOL.1/M1_97.PDF.
[xix] Bayer, A., Al-Omari, I., & Tromm, W. (1989). Dispersion of radionuclides and radiation exposure after leaching by groundwater of a solidified core-concrete (No. KFK-4512). Available http://www.irpa.net/irpa8/cdrom/VOL.1/M1_97.PDF
[xx] “TEPCO Announced Record Cesium Level Found in Groundwater Beneath Fukushima Levee” The Asahi Shimbun (February 14, 2014): http://ajw.asahi.com/article/0311disaster/fukushima/AJ201402140041). The article said that cesium found in groundwater under a coastal levee near unit 1 spiked from 76,000 Becquerels per liter on February 12, 2014 to 130,000 Becquerels per liter on February 13, reaching the highest level of cesium ever detected at that location.
[xxi] Record strontium-90 level in Fukushima groundwater sample last July. (2014, February 7). The Japan Times. Available http://www.japantimes.co.jp/news/2014/02/07/national/record-strontium-90-level-in-fukushima-groundwater-sample-last-july/#.U2XIw17K3yh.
[xxii] Lori Mochizuki, “31,000,000 Bqm3 Strontium 90 Measured Nearest Boring Well Reactor 2,” Fukushima Diary (January 2015) http://fukushima-diary.com/2015/01/31000000-bqm3-strontium-90-measured-nearest-boring-well-reactor-2). TEPCO document available: http://www.tepco.co.jp/nu/fukushima-np/f1/smp/2015/images/2tb-east_15012701-j.pdf
[xxiii] Lori Mochizuki (Fukushima Diary 590,000,000 Bq/m3 of Strontium-90 measured from groundwater of Reactor 2 seaside).
[xxiv] Lori Mochizuki, “1,000,000 Bq/m3 of Sr-90 detected in seawater of Fukushima plant port / Highest in recorded history,” Fukushima Diary (June 20, 2015) http://fukushima-diary.com/2015/06/1000000-bqm3-of-sr-90-detected-in-seawater-of-fukushima-plant-port-highest-in-recorded-history/ and TEPCO document http://www.tepco.co.jp/nu/fukushima-np/f1/smp/2015/images/2tb-east_15061901-j.pdf.
[xxv] Lori Mochizuki, “Highest Strontium-90 density detected in seawater of Fukushima plant port / 1,500,000 Bq/m3,” Fukushima Dairy (July 18, 2015). http://fukushima-diary.com/2015/07/highest-strontium-90-density-detected-in-seawater-of-fukushima-plant-port-1500000-bqm3/ TEPCO document available here: http://www.tepco.co.jp/nu/fukushima-np/f1/smp/2015/images/2tb-east_15071701-j.pdf
[xxvi] S. Kimura (6 April 2013) ‘120 Tons of Contaminated Water Leaks at Fukushima Nuclear Plant’, The Asahi Shimbun, http://ajw.asahi.com/article/0311disaster/fukushima/AJ201304060038, date accessed 7 April 2013.
[xxvii] Yoshida ‘Fukushima No. 1 Can’t Keep its Head Above Tainted Water’.
[xxviii] NRA signs off on TEPCO plan to release decontaminated groundwater into sea January 22, 2015 http://ajw.asahi.com/article/0311disaster/fukushima/AJ201501220054).