On 11 March, 2011, a massive magnitude 9.1 earthquake shook the west coast of Japan, with the epicenter located at a shallow depth of 32 km, a mere 72 km off the coast of Oshika Peninsula, of the Touhoku region. Following this earthquake, an equally massive tsunami made its way towards Japan’s eastern shores, flooding many kilometers inland. Over 20,000 people were killed by the tsunami and earthquake, thousands of whom were dragged into the ocean when the tsunami retreated. This Touhoku earthquake was the most devastating in Japan’s history, both in human and economic cost, but also in the effect it had on one of Japan’s nuclear power plants: the six-unit Fukushima Daiichi plant.
In the subsequent Investigation Commission report by the Japanese Diet, a lack of safety culture at the plant’s owner (TEPCO) was noted, along with significant corruption and poor emergency preparation, all of which resulted in the preventable meltdown of three of the plant’s reactors and a botched evacuation. Although afterwards TEPCO was nationalized, and a new nuclear regulatory body established, this still left Japan with the daunting task of cleaning up the damaged Fukushima Daiichi nuclear plant.
Removal of the damaged fuel rods is the biggest priority, as this will take care of the main radiation hazard. This year TEPCO has begun work on removing the damaged fuel inside the cores, the outcome of which will set the pace for the rest of the clean-up.
Safety Cheese Holes
The Fukushima Daiichi nuclear power plant was built between 1967 and 1979, with the first unit coming online in 1970 and the third unit by 1975. It features three generations of General Electric-designed boiling water reactors of a 1960s (Generation II) design. It features what is known as a Mark I containment structure. At the time of the earthquake only units 1, 2 and 3 were active, with the quake triggering safeties which shut down these reactors as designed. The quake itself did not cause significant damage to the reactors, but three TEPCO employees at the Fukushima Daiichi and Daini plants died as a result of the earthquake.
A mere 41 minutes later the first tsunami hit, followed by a second tsunami 8 minutes later, leading to the events of the Fukushima Daiichi accident. The too low seawall did not contain the tsunami, allowing water to submerge the land behind it. This damaged the seawater pumps for the main and auxiliary condenser circuits, while also flooding the turbine hall basements containing the emergency diesel generators and electrical switching gear. The backup batteries for units 1 and 2 also got taken out in the flooding, disabling instrumentation, control and lighting.
One hour after the emergency shutdown of units 1 through 3, they were still producing about 1.5% of their nominal thermal power. With no way to shed the heat externally, the hot steam, and eventually hydrogen from hot steam interacting with the zirconium-alloy fuel rod cladding, was diverted into the dry primary containment and then the wetwell, with the Emergency Core Cooling System (ECCS) injecting replacement water. This kept the cores mostly intact over the course of three days, with seawater eventually injected externally, though the fuel rods would eventually melt due to dropping core water levels, before solidifying inside the reactor pressure vessel (RPV) as well as on the concrete below it.
It was attempted to vent the steam pressure in unit 1, but this resulted in the hydrogen-rich air to flow into the service floor, where it found an ignition source and blew off the roof. To prevent this with unit 2, a blow-out panel was opened, but unit 3 suffered a similar hydrogen explosion on the service floor, with part of the hydrogen also making it into the defueled unit 4 via ducts and similarly blowing off its roof.
The hydrogen issue was later resolved by injecting nitrogen into the RPVs of units 1 through 3, along with external cooling and power being supplied to the reactors. This stabilized the three crippled reactors to the point where clean-up could be considered after the decay of the short-lived isotopes present in the released air. These isotopes consisted of mostly iodine-131, with a half-life of 8 days, but also cesium-137, with a half-life of 30 years, and a number of other isotopes.
Nuclear Pick-up Sticks
Before the hydrogen explosions ripped out the service floors and the building roofs, the clean-up would probably have been significantly easier. Now it seemed that the first tasks would consist out of service floor clean-up of tangled metal and creating temporary roofs to keep the elements out and any radioactive particles inside. These roof covers are fitted with cameras as well as radiation and hydrogen sensors. They also provide the means for a crane to remove fuel rods from the spent fuel pools at the top of the reactors, as most of the original cranes were destroyed in the hydrogen explosions.
This meant that the next task is to remove all spent fuel from these spent fuel pools, with the status being tracked on the TEPCO status page. As units 5 and 6 were undamaged, they are not part of these clean-up efforts and will be retained after clean-up and decommissioning of units 1-4 for training purposes.
Meanwhile, spent fuel rods were removed already from units 3 and 4. For unit 1, a cover still has to be constructed as has has been done for unit 3, while for the more intact unit 2 a fuel handling facility is being constructed on the side of the building. Currently a lot of the hang-up with unit 1 is the removal of debris on the service floor, without risking disturbing the debris too much, like a gigantic game of pick-up sticks. Within a few years, these last spent fuel rods can then be safely transported off-site for storage, reprocessing and the manufacturing of fresh reactor fuel. That’s projected to be 2026 for Unit 2 and 2028 for Unit 1.
This spent fuel removal stage will be followed by removing the remnants of the fuel rods from inside the RPVs, which is the trickiest part as the normal way to defuel these three boiling-water reactors was rendered impossible due to the hydrogen explosions and the melting of fuel rods into puddles of corium mostly outside of the RPVs. The mostly intact unit number 2 is the first target of this stage of the clean-up.
To develop an appropriate approach, TEPCO relies heavily on exploration using robotic systems. These can explore the insides of the units, even in areas which are deemed unsafe for humans and can be made to fit into narrow tubes and vents to explore even the insides of the RPVs. This is how we have some idea of where the corium ended up, allowing for a plan to be formed for the extracting of this corium for disposal.
Detailed updates on the progress of the clean-up can be found as monthly reports, which also provide updates on any changes noted inside the damaged units. Currently the cores are completely stable, but there is the ongoing issue of ground- and rainwater making it into the buildings, which causes radioactive particles to be carried along into the soil. This is why groundwater at the site has for years now been pumped up and treated with the ALPS radioactive isotope removal system. This leaves just water with some tritium, which after mixing with seawater is released into the ocean. The effective tritium release this way is lower than when the Fukushima Daiichi plant was operating.
In these reports we also get updates on the robotic exploration, but the most recent update here involves a telescoping robot nicknamed ‘Telesco’ (because it can extend by 22 meters) which is tasked with retrieving a corium sample of a few grams from the unit 2 reactor, in the area underneath the RPV where significant amounts of corium have collected. This can then be analyzed and any findings factored into the next steps, which would involve removing the tons of corium. This debris consists of the ceramic uranium fuel, the zirconium-alloy cladding, the RPV steel and the transuranics and minor actinides like plutonium, Cs-137 and Sr-90, making it radiologically quite ‘hot’.
Looking Ahead
Although the clean-up of Fukushima Daiichi may seem slow, with a projected completion date decades from now, the fact of the matter is that time is in our favor, as the issue of radiological contamination lessens with every passing day. Although the groundwater contamination is probably the issue that gets the most attention, courtesy of the highly visible storage tanks, this is now fully contained including with sea walls, and there is even an argument to be made that dilution of radioisotopes into the ocean would make it a non-issue.
Regardless of the current debate about radiological overreacting and safe background levels, most of the exclusion zone around the Fukushima Daiichi plant has already been reopened, with only some zones still marked as ‘problematic’, despite having background radiation levels that are no higher than the natural levels in other inhabited regions of the world. This is also the finding of the UNSCEAR in their 2020 status report (PDF), which finds levels of Cs-137 in marine foods having dropped already sharply by 2015, no radiation-related events in those evacuated or workers in the exclusion zone, and no observed effects on the local fauna and flora.
Along with the rather extreme top soil remediation measures that continue in the exclusion zone, it seems likely that within a few years this exclusion zone will be mostly lifted, and the stricken plant itself devoid of spent fuel rods, even as the gradual removal of the corium will have begun. First starting with small samples, then larger pieces, until all that will be left inside units 1-3 will be some radioactive dust, clearing the way to demolish the buildings, at the end of this long road.
since 2011, i have wondered why the various emergency core cooling systems (ECCS) didn’t function adequately. obviously, they weren’t up to the task, but i wish i understood more thoroughly why they were believed to be up to the task beforehand, and now known not to be. that’s important because new designs are supposed to be much better in this regard but that’s now a serial claim — “we solved the problem, as of the last revision”. it’s important to know why that claim, made 60 years ago, turned out to be false, if we are to evaluate how true it is today.
My understanding is that at the most basic level, they hadn’t prepared for a tsunami of that height – which meant it swamped and disabled much of the backup and safety systems.
I recall reading they also had on site diesel generator to provide backup power to run the cooling system but that got flooded and couldn’t work at all. All of the mess was because no one thought maybe the wall wouldn’t be high enough to block tsunami.
“they hadn’t prepared for a tsunami of that height”
Correct. The three other reactor sites on that very same coast, one not far north of Fukushima, had MUCH higher sea walls because they looked at a VERY long term historical record of tsunamis along that coast instead of what the designers of Fukushima did looking in the shorter term and they had no issues as a result. Even GE, the creator of the antique reactors they were using at Fukushima recommended a higher sea wall and above ground power backup. Supposedly for earthquake resistance, the diesel generator/battery backup rooms were underground in order to be anchored to bedrock which would have been OK if the sea wall had been high enough. They were flooded by the tsunami.
The generators in the basement would have been fine if the whole plant had been built higher up the shore as it was supposed to be in the original plans.
Dan’s spot on. In slightly more detail: ECCS, RCIC, and IC variously failed to do the job for long enough, as despite some being sensibly self-powered by steam from the reactor…the valves that operate them needed power to actuate. So some could not be turned on because AC was out (and the diesel backups flooded), and some could not be turned on because DC was out (after the batteries ran out/flooded). There’s the story of people grabbing car batteries to open the valves and/or run the control panel too. They were also for unit 1 turning on and off the IC cooling valves to limit the cooldown rate…and ran out of power with the valve shut. oops.
Each unit was a bit different in the timeline of how and when each bit went wrong. Note also that the low pressure cooling methods (including firehoses blasting water in) require you to vent the pressure vessel…this releases the radiation it was containing to atmosphere, (and as it turns out, hydrogen too for explosions). So I assume there was pressure to delay that action, on the incorrect hope that it could be avoided.
As someone who closely monitored the news during the time it happened, I can definitely attest that the mood in the international media was one that cautioned as much ability to avoid the hydrogen explosions as was possible. Even the choice to use seawater, which consigned the reactors to decommissioning, was heavily debated at the time.
There was only one village in japan that managed to withstand the tsunami. This was because their flood wall was 5 meters taller than the next nearby village. If you wanted to build an adequate defence around a nuclear plant, then it would be a good idea to emulate that.
https://en.wikipedia.org/wiki/Fudai,_Iwate
I think I read somewhere recently that the mayor of that village was vilified for overbuilding the flood wall, and that scorn hounded him even past his death — until the tsunami came, that is.
Easy to second guess when you know more facts afterwards by several years, hard as heck to predict really odd one off occurrences when designing and even if you accurately predict, the bean counters wouldn’t pay for that. Who knew a soft drink spilled on a keyboard would cause a meltdown at 3 mile island?
“It sounds to me like a Pepsi Syndrome!”
– not Jimmy Carter
Wow! Google’s bots crawl Hackaday within 6 hours! The Google search
already returns “Who knew a soft drink spilled on a keyboard would cause a meltdown at 3 mile island?” in the comment above as the third search result.
I just finished reading multiple sources that describe the Three Mile Island partial meltdown. The Wikepedia article details improvised filter cleaning, misleading indicator lights, valves in the wrong position, pumps that failed, inadequate operator training, and a general misunderstanding plus mismanagement of the situation–the classic “many things had to all go wrong at once.” I was unable to find documented evidence that a spilled drink or a keyboard of any sort was responsible for the accident. Snopes has nothing to say, so maybe this is not a myth.
@Piotrsko if you would be willing to share your sources, we would be grateful. Thank you.
I was referencing a Saturday Night Live skit that was aired sometime after the TMI incident, where they said the mishap occurred because of a spilled Pepsi.
I’m not sure if [Piotrsko] was referring to the SNL skit humorously, or somehow believed that to be factual.
I just searched for the video but I only found a link on TikTok (yecch!)
“The Pepsi Syndrome” was a spoof on “The China Syndrome” a forgetable movie starring Jane Fonda about a power plant reactor meltdown.
Here’s a reddit link to the video (instead of TikTok)
And yes, it mentions Coke instead of Pepsi
https://www.reddit.com/r/LiveFromNewYork/comments/1bh2edu/the_pepsi_syndrome_an_epic_parody_of_the_1978/
Ah yes Ms Fonda:
“If you understood what communism was, you would hope, you would pray on your knees that we would some day become communist. . . . I, a socialist, think that we should strive toward a socialist society, all the way to communism.”
I tried Googling as well, I got one page stating it was Coke, not Pepsi and another page stating it was coffee. Since this happened 45 years ago and before “Al Gore invented internet”, anything we can find should be taken with a grain of salt.
“Easy to second guess when you know more facts afterwards by several years, hard as heck to predict really odd one off occurrences when designing”
The other three nuclear reactor sites along the same coast did just fine simply because they more reasonably analyzed a MUCH longer timeline of tsunamis in that area and built MUCH higher sea walls as a result. For those responsible for the Fukushima site wall height decision, most likely a decision just to save a few yen, it’s fortunate for them that the Japanese culture is no longer expecting Seppuku.
Cleanup is a necessary task, but I am much more interested in the root causes. I never understood why they build a nuclear plant on the coast in an area known to have earthquakes and Tsunamis. Years before this happened there were already several reports that the dykes would not be able to withstand a tsunami.
And I understand Japan is low on flat land, but you can build 90% of the nuclear plant on the beach, but don’t put the pumps in the cellar, place them on the roof so they keep working when the whole thing is flooded.
It’s mind boggingly stupid that very big slipups like this do not get caught during the design of a nuclear power plant. Engineers are smart enough to do it right, it’s often politics that takes shortcuts.
And there is always the underestimation of the ingenuity of a true fool. How do you calculate that into the safety of a nuclear power plant?
i think we have learned a lot from the big 3 nuclear disasters to improve reactor designs and to be better at contingency planning. but the fact that much of the nuclear base is old 2nd gen reactors is somewhat alarming. you can amend procedures and do systems upgrades on those, but you cannot remove any inbuilt deficiencies without rolling out a new design.
human error is always going to be a problem, 2 of the big 3 were caused by operator error, and the 3rd perhaps though poor contingency planning and lack of failsafe design. pride, hubris and money are known to stifle safety culture and none of them belong in the control room or anywhere inside the fence for that matter.
the important thing is to learn from the event and apply those lessons to the nuclear industry as a whole, in the same way air travel does. air travel does kill more people than nuclear incidents, yet it is viewed as being worth the cost, otherwise we wouldn’t do it. by meticulously analyzing every incident we have increased its safety by leaps and bounds. that’s the attitude you need to have with nuclear. just dont boeing it up.
“big 3 nuclear disasters”?
OK, we get Fukishima and Chernobyl. What’s the 3rd? Windscale (like the Chernobyl fire, but 30 years previous)? SL-1 (a test reactor, maybe doesn’t count)? K-431 (a submarine reactor, does that count)? Surely not Three Mile Island (some property damage, no deaths or injuries, but lots of American media FUD)?
TMI was a partial meltdown, why wouldn’t it count? Really speaks volumes that you require loss of life to consider it a disaster…
But ranked 3rd, ahead of at least three other bigger incidents that did have loss of life? TMI was just property damage, nobody got hurt.
Probably Three Mile Island.
The Kyshtym disaster was the 3rd worst accident.
Lucens in Switzerland
https://www.swissinfo.ch/eng/banking-fintech/radioactive_historic-nuclear-accident-dashed-swiss-atomic-dreams/44696398
To my mind there was no problem at all. The reactor had several failsafes, all designed with additional margin over what was reasonably expected. The designers had literally anticipated everything that could go wrong and built accordingly. What happened was a combination of events at a greater scale than anyone would have imagined (except armchair engineers with 20/20 hindsight).
As to “why they build a nuclear plant on the coast in an area known to have earthquakes and Tsunamis”, well, Japan is made of coast, and it suffers from earthquakes everywhere. They could have built it in Korea or China, I suppose, but they can’t do that these days.
Except for building the whole plant lower to the shore than they were actually permitted, to save on pumping costs, and having the change in plans approved through corruption.
You didn’t provide a citation, so I looked it up. I guess the designers did anticipate everything, but TEPCO ignored them. Oh well.
During the Fukushima disaster there was a popular narrative in the press, that Japanese politics after World War II had put their budding nuclear power industry in a terrible bind. Plant owners and regulators couldn’t fully admit that disasters were possible, so they did not properly prepare for them (e.g. comprehensive “run books“ detailing what to do in specific disaster scenarios). I would not be surprised if the height of seawalls and the location of power plants were influenced by this denialism. Human beings are terrible at reasoning about “the long tail” of risk. We need look no further than the 2008 mortgage-backed securities crisis. “Let’s bundle sub-prime mortgages from Florida and Nevada to reduce risk. They can’t possibly correlate. What can go wrong?“
I read the other day that a common office role for American expats in Japan is that of the “loud American guy,” being that Japanese office culture (to use a generalization) doesn’t normally allow flagrant criticism of the boss in front of the whole team. But sometimes time is sensitive and negative feedback can be beneficial immediately. Enter: Loud American, who isn’t expected to follow Japanese etiquette flawlessly and just speaks his mind when he wants to. Sometimes it will be his only significant duty.
Sounds like a job for a Texan!
B^)
I work in the UK and i can assure you that loud American girl is a big part of our science industry and we look forward to it coming to an end.
You haven’t met the German guy, have you?
Pumps can only suck water so high. As the vacuum increases you reach a point where the water starts boiling. This causes cavitation which destroys the pump.
This outstanding series just broadcast their episode about Fukushima. That’s where I got the info for my comments above with the exception of GE’s warning to the company running Fukushima about the vulnerability of the backup power system flooding:
Disaster Autopsy
S1E7 – Fukushima, Manhattan Crane, Forrestal
Three real-world disasters forensically dissected: Fukushima nuclear plant, a Manhattan crane collapse, fire on the aircraft carrier USS Forrestal.
https://www.nationalgeographic.com/tv/episode/d336d444-9709-43ec-ad67-ac988f19f80b/playlist/PL551127435
Thanks for the link to the documentary, also available on Disney+. After watching the episode, which was interesting enough, I would humbly set expectation low: nice 3D graphics and archival footage, but minimal information content, typical of “History channel style” documentaries. (The segment is 15 minutes long. You could probably read the transcript in 3).
A more interesting documentary to track down would be on the heroic efforts to save the nearby Fukushima Daini nuclear power plant, which involved large teams of volunteer workers wrangling heavy emergency power cables to get the cooling water pumps working again. Spoiler: they succeeded.
Building the emergency generators and their fuel supplies a few km further from the ocean would have allowed the generators to continue to function after the reactors were shut down. Even if the power lines were knocked down, it would be easier and take much less time to fix the power lines to restore power to prevent nuclear fuel meltdown or hydrogen gas explosions. Hauling in replacement generators was not possible because of the tsunami damage and the time it would take.
One hopes that, in the United States, the managers of nuclear power plants near the ocean reviewed the locations of their emergency power generators to insure emergency power interruption would not occur from a tsunami or hurricane in case the connection to the grid were to be broken.
Nuclear power is a lot like ‘tickling the dragons tail’. We can justify the use of it as long as nothing really goes wrong and creates at the very least a big expensive mess – ruining the economics of it’s use in the first place. Six months after Fukushima in 2011 there was a big earthquake (5.8 magnitude) centered about 15 miles from the North Anna Nuclear Plant in Virginia which was designed to take up to a 6.2 magnitude quake.
From wikipedia:
The Nuclear Regulatory Commission’s estimate of the risk each year of an earthquake intense enough to cause core damage to the reactor at North Anna was 1 in 22,727, according to an NRC study published in August 2010.
During the construction of original nuclear reactors at North Anna, the utility learned of fault lines within the construction site of the proposed plants from its outside independent engineering firm, Stone & Webster, who the utility had hired to assess the proposed nuclear plant locations. The government fined the utility $32,000.00 for concealing this information.[23]
According to the Huffington Post, this 1977 Justice Department memo “..focused on how the power company and federal regulatory officials went to efforts to not make public the knowledge of geologic faulting at North Anna. “[V]irtually the entire Office of Regulation of the [Nuclear Regulator Commission was]… well aware of the fault and determined not to take any immediate action,” according to the memo. A government attorney, Bradford Whitman, did not recommend prosecution at the time, but the power company was eventually fined $32,500 for making false statements during the licensing process, according to the DOJ memo
https://en.wikipedia.org/wiki/North_Anna_Nuclear_Generating_Station
https://www.facingsouth.org/2011/08/earthquake-scare-at-virginia-nuclear-plant-comes-as-regulators-drag-feet-on-addressing-indus
Crushing energy independence and therefore geopolitical power in certain zones is one of the primary unpublicized goals of both decarbonization as well as denuclearization, which is why the latter isn’t proposed as a solution to the former, and all sorts of excessive hysteria is stoked around the three or so significant incidents in the history of the technology.
Exactly this!
I wonder if there is an (ongoing) analysis of the costs of the whole situation. Since management seems not interested in soft topics as human resources, the monetary estimates would maybe be interesting to them?
It is a massive undertaking to do a complete economic analysis, on macroeconomic and microeconomic scales. But personally, I think Fukushima Daichi would be a highly interesting case study.