PART 2.1:
Issues at Fukushima Daiichi Nuclear Powerplant (FDNPP)
MARCH 2015
A note before we start:
Compared to 2011, the Fukushima crisis is evolving more slowly that it had been. Nevertheless, it is difficult to keep up with changing circumstances and new information. While the core of SAFECAST’s work is making crowdsourced environmental monitoring data freely available online, we’ve also gathered a large store of data on issues such as the condition of the Fukushima Daiichi plant itself, the situation for evacuees, environmental consequences of the accident, food risks, and health issues. From the start we have made a point of talking to researchers regardless of their ideological stance on nuclear power, and over the past several years have fielded countless questions and requests for data, which we’ve always tried to respond to positively. The robustness of this dialogue has also made it possible for us to seek expert advice and opinion on many related subjects, and to pass this knowledge on to our community as well.
From time to time we have published in-depth blog posts on specific subjects, and made technical backgrounders available online, and have often pointed researchers, journalists, and others towards these to help them get up to speed. Quite a lot of technical information and many scientific reports are discussed, sometimes heatedly, on the Safecast Radiation Discussion Google Group. The following Situation Report is an attempt to compile and summarize the most relevant, current, and accurate information we are aware of on the major aspects of the Fukushima disaster and make it available as a reference for anyone who is interested or has a need to know. Not surprisingly, we have been forced to leave out as much as we’ve included, but have taken pains to make it readable, and provide links to more in-depth documents wherever possible.
Every aspect of this disaster is accompanied by controversy, and we carefully guard against our own biases and strive to be as open and inclusive as possible. Some people will undoubtedly find that our information in some places contradicts what they’ve been led to believe. Others will feel we do not give sufficient weight to one opinion or another. We have concentrated on finding the best-documented sources, and have attempted to evaluate the evidence dispassionately. We welcome criticism, and urge anyone who would like to point out contradictory data not to hesitate to do so, because that is a challenge we particularly welcome. As mentioned above, we intend to update the Safecast Report on a regular basis, and would be pleased with any feedback which will help us improve it.
About information sources
The reliability of information has always been a major issue affecting our understanding of the Fukushima Disaster, and in fact the lack of reliable information during the early stages of the disaster was the reason SAFECAST was founded. In the following sections we describe the current situation at the Daiichi site itself, for the environment in general, for food, and for people’s health, and cite our sources of information in each case.
Official statements concerning ambient radiation levels in the environment, and to a lesser degree soil contamination, can be crosschecked against citizen science and academic research in most cases. Radiation levels and impacts in the ocean, with the exception of the immediate vicinity of Daiichi, have been very well documented by researchers, in a way which provides a useful cross-check against official claims concerning releases of contaminated water to the ocean, etc.. Food testing data from many independent groups is available as well as from the government. There has been little or no third-party verification of the decontamination process itself, but radiation levels can be easily confirmed for most locations if desired. Verifying the health monitoring done by the national and Fukushima Prefecture governments presents a higher technical hurdle, but several well-done health screening programs run by local governments as well as by community groups and foundations allow many useful comparisons to be made.
But for understanding what’s happening onsite at the Daiichi plant itself, we are forced to depend on data provided by TEPCO almost exclusively, much of it presented with an obvious PR spin. Because there is almost no independent verification of measurements and work onsite, this data has an inherent unverifiability which in some cases can be significant. SAFECAST has consistently pushed for third-party verification of radiation monitoring at the Daiichi site and elsewhere, and while some TEPCO staff and gov’t agency employees have privately agreed that it would be beneficial for everyone, including TEPCO itself, to adopt this kind of policy, none of our proposals have been accepted so far. Other qualified groups and researchers we know have made similar proposals and have also been rebuffed. But we won’t give up, and will continue to press for the inclusion of third-party monitoring as a matter of course.
In the following sections, we begin with a general summary of each topic, followed by more in-depth discussion.
Acknowledgements:
Many thanks to Andrew Pothecary, designer of many of the infographics which appear on throughout the Situation Report section. Many of these previously appeared in the Number 1 Shimbun, the magazine of the Foreign Correspondents’ Club of Japan (FCCJ) and are credited as such, while others were made specifically for this report. We would also like to thank the many researchers and specialists who have given us valuable feedback on our drafts. Of course any errors are our own.
2.1- Issues at Fukushima Daiichi Nuclear Powerplant (FDNPP)
There are many continuing issues of concern at the Fukushima Daiichi site itself, and how quickly and well they are resolved will greatly influence the ultimate severity of the effects to the environment and to people’s health. We quickly summarize the current status of decommissioning, removal of spent fuel rods, water problems, and other issues.
Organizational acronyms:
JAEA: Japan Atomic Energy Agency
IAEA: International Atomic Energy Agency
NIRS: National Institute of Radiological Sciences
NRA: (Japan) Nuclear Regulatory Authority
METI: Ministry of Economy, Trade, and Industry
MEXT: Ministry of Education, Culture, Sports, Science and Technology
IRID: International Research Institute for Nuclear Decommissioning
2.1.1 — Decommissioning roadmap
Briefly put, everything that is being done now and which will be done on site until the year 2020 is merely preparation for the really hard work of removing the melted fuel. There is a roadmap, and TEPCO is basically on schedule so far, but it gets much harder from this point forward. There is regulatory oversight, but we don’t think it’s intrusive enough.
TEPCO released it’s first decommissioning roadmap — a timeline describing the expected schedule of work on the cleanup of the Daiichi site — in Dec. 2011, and has issued periodic updates, most recently through METI on Jan 29, 2015. It’s a complicated document that points to the ultimate removal of melted fuel from the reactor containments at some as yet unknown date in the future, demolition of the buildings themselves, and remediation of the site. Much of the actual planning for later stages of the work cannot be done until success has been assured on earlier stages, particularly in solving the many water-related problems on the site. In fact, some of the technologies expected to be required for actually extracting the melted fuel do not exist yet.
Mid-and-long-Term Roadmap towards the Decommissioning of Fukushima Daiichi Nuclear Power Units 1–4
This NRA document from Feb 2015 fills in a few details:
Measures for Mid-term Risk Reduction at TEPCO’s Fukushima Daiichi NPS (as of February 2015)
The overall long-term timetable has changed little since 2011, and is divided into three phases:
— Phase 1 (2012–2013): This involved stabilization and other work done prior to the start of removing spent fuel.
— Phase 2 (2014–2021): This is the current phase, and includes the continuing removal of spent fuel, and preparation for removing melted fuel debris from the reactor containments, including solving many water-related issues onsite.
— Phase 3 (2022 -?): This is the melted fuel removal and decommissioning process itself.
Many kinds of work are carried on concurrently, and TEPCO can be said to have met its primary goal for the end of Phase 1 and the start of Phase 2. In reality, the more detailed timelines are frequently adjusted, as are actual work targets, and often slip by months or longer. The 2014–2021 phase is very long, and this reflects the fact that many technologies do not exist for what needs to be done, and will require years of development. The melted fuel removal and decommissioning phase expected to start in 2022 currently has no estimated end point, though TEPCO has previously stated it would be 30–40 years from now. Based on prior experience at Three Mile Island and Chernobyl (where melted fuel has not yet started to be removed), we should assume it will require several decades.
TEPCO does not make its plans in isolation, but receives guidance and instructions from Japanese government agencies such as the METI, NRA, JAEA, NIRS, and IRID, and is required demonstrate to the IAEA that progress is being made onsite. NRA and IAEA conduct periodic reviews and onsite inspections, but we feel they lack the manpower, if not the mandate, to conduct the kind of unannounced daily inspections that seem to be warranted. The government seems to only know what TEPCO tells it, and the IAEA seems to depend primarily on information provided by the Japanese government. We’re left to conclude that the only entity which really knows what’s happening onsite is TEPCO itself, and that it is able to be selective about what data it releases, how, and when. The IAEA’s most recent (preliminary) inspection report was issued on Feb 17, 2015. Documents released by UN agencies invariably adhere to a thick diplomatic language which requires a fair amount of parsing and reading between the lines. Not surprisingly, however, the IAEA reserved its strongest criticism for TEPCO’s failures of management and oversight. Partly because of continued problems in these areas, we suspect, new corporate entities, the Fukushima Daiichi Decontamination and Decommissioning Engineering Company and the Nuclear Damage Compensation and Decommissioning Facilitation Corporation, have recently been established, intended to improve oversight of these critical long-term projects.
9–17 February 2015
Summary of decommissioning and contaminated water management, Jan 29, 2015
2.1.2 — Spent fuel pools
Despite loud portents of doom in the global media, TEPCO succeeded in safely removing all of the spent fuel from Unit 4. This unit had the most fuel to remove, but the remaining three units will almost certainly be harder. The last are due to start being emptied in 2017. This fuel needs more secure long-term storage than in the common pool onsite, though there’s really noplace else to put it yet.
One of the most critical ongoing tasks is the removal of hazardous spent fuel assemblies from the spent fuel pools of Units 1, 2, 3, and 4 (Unused fuel assemblies also need to be removed, but are not as hazardous). The process poses unique engineering and worker protection challenges, and serious mishaps could have wider negative consequences for the public and the environment.
Unit 4:
The removal of 1533 fuel rods from Unit 4’s spent fuel pool was successfully completed without mishap on Dec. 22, 2014. The process necessitated removing a large quantity of rubble and dismantling unneeded upper structure, building a very large, multistory structure which cantilevered over the damaged reactor building, to stabilize it while not imposing any additional load, and installing new fuel handling machinery. The removed fuel assemblies were placed in fuel transfer casks, 71 times in all, and trucked a short distance to the common pool onsite at Daiichi, where it is expected to be stored for 10–20 years, and then transferred to more secure storage (though the decisions about how and where remain to be made). Prior to the commencement of this operation and throughout there were very loud and alarming claims from many quarters that failure was likely and that mishaps would lead to the extinction of the human race. Because we had looked closely at the seismic stability and structural damage reports for Unit 4 beforehand, we considered these claims to be extremely exaggerated, and in fact, giving credit where it is due, we have been impressed by the engineering design of this particularly challenging and unprecedented project. It can now function as proof of concept for the removal of spent fuel from the remaining reactor units.
Tepco info page about decommissioning, including PR videos:
Unit 3:
According to the current roadmap, spent fuel will next be removed from Unit 3, commencing in fiscal 2015. Although the 566 assemblies that need to be removed (514 used, 52 unused) are far fewer than there were in Unit 4, Unit 3 is almost entirely inaccessible to workers because of high dose rates. Work onsite is being done remotely for this reason, and the removal of the fuel rods is expected to be done primarily remotely as well. Removal of rubble from the roof was completed in Oct. 2013. The spent fuel pool is also full of structural debris which has been carefully mapped and modeled in 3D to help guide the remotely controlled removal equipment. There have been mishaps, such as equipment accidentally dropped back into the pool while it was being removed, and highly radioactive dust being released while a large girder was being removed from the roof adjacent to the pool. Like Unit 4, Unit 3 will require a large structure which houses the necessary equipment to be erected in a way that places no extra load on the damaged reactor building.
TEPCO, Unit 3 spent fuel pool 3d debris maps etc, Jan 2015 (in Japanese)
Unit 2:
This spent fuel pool contains 615 fuel assemblies. Because this reactor did not suffer a devastating explosion like the others, the erection of a large separate structure will probably not be necessary. Nevertheless high dose rates will complicate the work, and the detailed plan has not yet been decided upon, though removal is currently being considered for commencement after fiscal 2017.
Unit 1:
This spent fuel pool contains 392 fuel assemblies, and the building is currently covered by a fairly lightweight structure intended to contain ongoing releases of radiation to the air, which will be dismantled in order to allow rubble to be removed. The final removal process has not yet been decided, but is being considered for commencement in fiscal 2017.
2.1.3 — Water problems
We hear a lot about the water problems at the Daiichi site because they’re serious and are an obstacle to starting the other work which needs to be done, and could directly affect the environment and marine life. If we could see the water that’s causing the most trouble things would be a lot easier, but we can’t because it’s underground. The difficulty of the water problems has forced TEPCO to think ambitiously and innovatively, and appears to be advancing technology in some areas. But most of the other leaks which make the news (because they can be easily detected) have very low-tech, easily preventable causes.
Most readers are undoubtedly aware that tremendous water problems exit onsite at Daiichi. The root case is that both water which has been being circulated through the damaged reactors to cool the melted fuel as well as groundwater which has been leaking through the site and into the buildings themselves become contaminated, though precisely what it is coming into contact with remains unclear. Several measures, which TEPCO calls “contaminated water countermeasures,” have been put in place to deal with various facets of the overall problem with varying degrees of success. Their approach can be divided into three main components, each of which involves several technologies:
- To effectively filter the cooling water which is being recirculated.
2. To prevent groundwater from coming into contact with radioactive materials.
3. To prevent contaminated water from leaking out into the environment.
TEPCO claims to be making progress in all these areas, which the IAEA reservedly cited in its recent report, but without independent confirmation of radiation levels in the water onsite it is impossible to be certain.
2.1.3.a — Radionuclide removal systems
The systems TEPCO uses for removing radionuclides from water onsite started as an unreliable hack, but have gradually grown and become more stable. It’s an incremental learning process that we’re very familiar with. TEPCO has spliced together several different systems to make it possible to scale up and add new capabilities, and initiate new technological developments. The overall system seems to be performing well now, but there are still several weak points where breakdowns could lead to even more delays in processing all the water that needs to be treated.
TEPCO currently uses several water treatment systems — ALPS, SARRY, and Kurion — to remove radionuclides from the recirculating water. ALPS (Advanced Liquid Processing System), designed to remove 62 nuclides, is the largest system, and after a number of initial problems, in recent months it has reportedly been able to remove cesium to levels below detection with adequate consistency. Initially, the SARRY (Simplified Active water Retrieval and RecoverY system) and Kurion systems (Kurion is the name of the manufacturer) also only removed cesium. None of the initial systems were designed to remove strontium, however, which is one reason much of the treated water has had to be stored and could not be released into the ocean. A new Kurion Mobile Processing System which can remove strontium began operating in Oct. 2014, and a second unit in Jan. 2015. The SARRY system was also upgraded to enable strontium removal. Tritium remains a problem. Though a few promising techniques have been demonstrated, tritium removal at this scale presently remains technologically unproven.
The IAEA feels confident that though it still contains tritium, if controlled releases of the treated water to the ocean were done there would be minimal impact to the environment, but this suggestion has unsurprisingly met with opposition from local fishermen. According to the IAEA, over 1 million cubic meters (m3) cumulative volume of water has been treated, and about 600,000 m3 of contaminated water is currently stored onsite, about half of which has been treated and the targeted nuclides also reduced to non-detectable levels. Construction of new tanks has barely outpaced the production of contaminated water, and periodic leaks from the tanks have highlighted deficiencies in management and oversight. TEPCO initially expected that the backlog of water to be treated would be completed by the end of fiscal 2014, but has recently pushed this target back by several months. It is unknown if and when an agreement to allow the release of water containing tritium will be reached. The alternative is to continue to build storage tanks onsite, until, perhaps, a viable large-scale tritium removal system is developed.
Kurion to Sign Contract Over Fukushima Cleanup, WSJ Sept. 17, 2014
2.1.3.b — Groundwater problems
Briefly put, the planned solution is an ambitious series of underground dams made of ice (frozen soil, to be exact), and dozens of pumps. The pump part would be easy if the water wasn’t radioactive. All the eggs are in this basket, and we haven’t heard of a plan “B” in case it fails. Unless the groundwater problem is solved, it won’t be possible to carry out the next steps to prepare for removing the melted fuel.
According to the IAEA and other sources, approximately 300 m3 of groundwater enters the reactor buildings per day, a problem which is rooted in the initial siting of the building. Though the ground level where the building sits was originally much higher, major excavation was done to lower the site in order to make the pumping of water from the ocean easier, bringing the buildings into contact with the permeable geological layers through which groundwater flows. Under normal conditions the buildings had an adequate seal against this water, as well as efficient “subdrain” pumps to remove it, but since the 2011 disaster large amounts of water have been entering the reactors, apparently through cracks or other openings underground. Exactly how and where remains a mystery. Several methods of dealing with this water are being tried.
— Sealing the buildings
Sealing any below ground-level openings in the reactor buildings would seem to be the best and most direct option for keeping groundwater out, and efforts are being made to identify where the leaks are and to develop sealing methods. But the radiation levels inside and next to the reactor buildings are generally too high to allow humans to work for any length of time. In fact, radiation in many parts of the buildings is high enough to give lethal exposures within a short time (over 5000 mSv/hr in Unit 1, 4400 mSv/hr or over in Units 2 and 3). Techniques for repairing cracks and other gaps remotely are being investigated, and are expected to be required in order to prepare the structures for the removal of melted fuel after 2022, but they do not currently exist. In the meantime the groundwater causes so many other problems that it must be dealt with soon.
— Groundwater Bypass
Because the groundwater is flowing into the site from the mountains on the side opposite the ocean, it has been hoped that intercepting as much of this water as possible before it reaches the site could greatly reduce the amount reaching the reactor buildings. Groundwater on the uphill mountain side so far has not shown high levels of radioactive contamination, so after an agreement was reached with local fishermen to have it stored and independently tested before being released — the only agreement of this sort reached so far — the pumping and diversion of the water was begun in April 2014. The IAEA says that this has reduced groundwater ingress by approximately 25%, not as much as was hoped, but an improvement nonetheless.
— Subdrains
A system of about 40 drain pumps, called “subdrains,” located near the reactor and turbine buildings, existed prior to the accident. These were intended to mitigate potential problems from groundwater during normal operation of the plant, but were seriously damaged and have been unusable since March 2011. Repairs to this system are reportedly nearly complete. Once back in operation, the subdrain system should initially be able reduce the amount of water entering the buildings by 150 m3 per day, according to the IAEA (TEPCO’s own estimate is 500–700 tons, roughly 500–700 m3). Once the frozen earth wall is successfully in operation, these drains should theoretically be able to reduce water inflow to zero. This water will be purified and stored in tanks, like the water from the groundwater bypass, and subject to similar third-party monitoring conditions and the approval of local fishermen before any is released. But due to increased opposition from the local fishermen’s union in the wake of recent revelations that other contaminated water has been secretly released from the plant, such an agreement may be difficult to reach.
Groundwater pump-up by Subdrain or Groundwater drain
— Frozen underground wall
After examining several alternatives, TEPCO decided upon a controversial plan to construct a 30 meter-deep wall, or dam, of frozen earth around the reactor buildings in hopes that this will provide an effective barrier to water ingress. The planned structure, called the “land-side impermeable wall,” will form a rectangle approximately 500m by 200m, with a total perimeter of about 1500m. Though the frozen earth technique is well-proven and is often used in very challenging mining and tunneling operations, the wall at Daiichi is the longest ever actually attempted, and is being done with an ever-present radiation hazard as well as many underground obstacles. Onsite tests began in August 2013, construction began in June 2014, and the freezing operation is now due to start in April, 2015. If all goes according to plan, the wall will greatly reduce the water inflow, but much about the plan remains unpredictable. If the water pressure outside the buildings is less than it is inside, for instance, they are likely to continue leaking, possibly more than before. TEPCO seems to hope that any leakage will be contained within the perimeter of the frozen wall, and intends to pump water in and out to maintain the proper pressure levels. Again, while we believe that the overall plan is technically sounder than many critics have claimed, we think the challenges should not be underestimated and we retain some skepticism. Even if it is only partially successful at lowering the groundwater level onsite, however, it should make other aspects of the work easier in the future.
— Sea-side impermeable wall
Groundwater samples taken from observation wells in the area between the reactor buildings and the ocean front (intake and port areas) have regularly shown high levels of radionuclides, particularly gross beta (which includes strontium) but also cesium. In Oct. 2014, samples from one set of wells showed over 7.8 million Bq/L gross beta, which declined to 500,000 Bq/L by Jan. 2015. Although the total radiation levels are many thousands of times lower than they were in March and April, 2011, this kind of contaminated water has continued to seep into the ocean, primarily contaminating and recontaminating the seabed offshore. While the continuing releases are notable and need to be stopped, as far as we can tell, even after several years at the current rates they will probably add less than 1% to what the initial releases dumped. To stop this seepage, TEPCO has constructed a 30m deep wall of sheet pilings called the “sea-side impermeable wall” along the ocean frontage of the site, about 780m in total length, and as of Jan. 2015 this was 98% complete. An approximately 10m wide opening still remains, and though we have not yet found clear information from TEPCO about it, we conjecture that it will be left until the results of the frozen wall become clear. In the meantime it allows a limited flow of contaminated groundwater into the partially-enclosed port area. TEPCO regularly releases test data for water taken from the port area as well as from offshore (see section 2.3.3 — The Ocean), but we feel that not all relevant locations are covered, and reiterate that without independent confirmation some skepticism remains about the accuracy of the figures TEPCO provides.
Analysis Results of Groundwater Obtained around Fukushima Daiichi NPS, March 20, 2015
Analysis Results of Seawater Obtained around Fukushima Daiichi NPS
— Trenches
Each of the reactor turbine buildings is connected to seawater intake pumps and other equipment at the waterfront by interconnected underground tunnels called trenches, for seawater piping and power cables primarily, as well as a number of connecting shafts and smaller underground structures. The trenches of Units 2 and 3 in particular became filled with several thousand tons of highly contaminated water during the early phase of the disaster, and due to continuing leaks and poorly-understood flow mechanisms, now appear to contain a mixture of contaminated cooling water and groundwater. This water must be removed before the freezing of the earth wall can be done nearby. TEPCO considered several methods, and began by attempting to make frozen plugs at one end of the seawater piping trenches of Unit 2, which they hoped would allow the water to be easily pumped out and treated afterward, and could be repeated at Unit 3’s trenches. The method apparently worked in experiments but failed in practice. In Nov. 2014 TEPCO started pumping water out of the Unit 2 seawater piping trench, making it possible to pour a concrete special cement mix (grout), which was completed in mid- Dec. 2014. As of Feb. 2015, the same procedure was being used for the seawater piping trenches of Unit 3 and Unit 4.
Progress of blocking water at connection of trenches and the Units 2 / 3 reactor facilities July 23 2014
2.1.4 — Melted fuel removal
This has only really been once before, at Three Mile Island, where melted core removal was completed in 1990 (it has not yet been attempted at Chernobyl), so there are not many people with experience to call on for assistance. The job is too big for any one company to tackle, so a new, well-funded research institute has been established to incubate the kinds of technologies that will be necessary. The process will require decades.
Removing melted fuel from inside the damaged reactors and storing it safely is the primary goal of the decommissioning process. As mentioned above, this will not actually start until around 2022. Fundamentally, everything that has been done onsite until now and which will be done until the actual removal process begins is preparation for that stage. Because of the tremendous technical challenges involved, which exceed the experience and know-how of any existing single company, the International Research Institute for Nuclear Decommissioning (IRID) was established in 2013. This consortium is under the guidance of the Japan Atomic Energy Agency and the National Institute of Advanced Industrial Science and Technology, and includes as founding members major corporations such as Toshiba, Hitachi-GE Nuclear Energy, Ltd., and Mitsubishi Heavy Industries, Ltd., as well as major electric utilities from around the nation. IRID’s primary mission is to research and develop the necessary technologies for decommissioning the nuclear reactors, which it seeks to do in cooperation with companies and organizations both inside and outside of Japan.
IRID has been very active, seeking and funding proposals and organizing meetings and workshops, some of which have had tangible results, but it is still far too early to make any firm decisions about how the actual melted fuel removal work will be done. The current front-running idea, however, is called the “submersion method.” This involves plugging leaks in the reactor containment so it can be filled with water, and then using remote-controlled machinery inserted from above on long telescoping arms to cut up and extract the melted fuel in pieces. The following video explains the process under consideration:
IRID Explanatory video for Submersion Method for Fuel Debris Retrieval, May 2014
Before this can be done, the melted fuel must be located, the reactor buildings decontaminated and shielded so that workers can enter, power and communications re-established inside the buildings, and methods developed to minimize the further spread of contamination during the decommissioning process. Meanwhile, though some initial progress has been made, most of the robotic equipment necessary to survey inside the torus rooms and lower levels of the containment buildings is still being developed. This is necessary both to identify places that need repair prior to submersion, and also to locate the melted fuel itself. The sobering reality is that the technology for dealing with most of the tasks that melted fuel removal will entail does not yet exist.
Muons are subatomic particles that are created when cosmic rays pass through the Earth’s upper atmosphere. The use of muon tomography for locating melted fuel has met with considerable success in tests, and equipment was installed outside Unit 1 on March 10, 2015. The detection system currently being installed measures the number and trajectory of muons after they have passed through objects. Because nuclear materials are denser than other metals and concrete, their location can be readily identified using this technology, much like an X-Ray. The team, led by the High Energy Accelerator Research Organization (KEK), reported their results on March 20, 2015, saying that nuclear fuel was not detected within the reactor containments, lending strength to the assumption that it all melted and dropped to the concrete floor below. Measurements at Unit 2 using a different type of muon detection system developed by Toshiba is expected to be begin onsite around October of this year, though a team from Nagoya Univ. was also reported to have done similar scan tests at Unit during 2014; at the time of this writing those findings have not yet been made available.
Reactor imaging technology for fuel debris detection by cosmic ray muon Measurement status report in Unit-1 March 19, 2015
Placement of muon detectors, Feb. 9, 2015 (in Japanese)
COMMENCEMENT OF REACTOR INTERIOR SURVEY USING ‘MUON PERMEATION METHOD’ (FEBRUARY 12, 2015)
Tokyo Electric Power : Nagoya University confirms Fukushima No. 2 reactor meltdown
(end of section 2.1)
TO OTHER SECTIONS:
2.1- Issues at Fukushima Daiichi Nuclear Powerplant (FDNPP)
