Clearing the radioactive rubble heap that was Fukushima Daiichi, 7 years on — Scientific American

” Seven years after one of the largest earthquakes on record unleashed a massive tsunami and triggered a meltdown at Japan’s Fukushima Daiichi nuclear power plant, officials say they are at last getting a handle on the mammoth task of cleaning the site before it is ultimately dismantled. But the process is still expected to be a long, expensive slog, requiring as-yet untried feats of engineering—and not all the details have yet been worked out.

When the disaster knocked out off- and on-site power supplies on March 11, 2011, three of the cooling systems for the plant’s four reactor units were disabled. This caused the nuclear fuel inside to overheat, leading to a meltdown and hydrogen explosions that spewed out radiation. The plant’s operator, Tokyo Electric Power Co. (TEPCO), responded by cooling the reactors with water, which continues today. Meanwhile thousands of people living in the surrounding area were evacuated and Japan’s other nuclear plants were temporarily shut down.

In the years since the disaster and the immediate effort to stanch the release of radioactive material, officials have been working out how to decontaminate the site without unleashing more radiation into the environment. It will take a complex engineering effort to deal with thousands of fuel rods, along with the mangled debris of the reactors and the water used to cool them. Despite setbacks, that effort is now moving forward in earnest, officials say. “We are still conducting studies on the location of the molten fuel, but despite this we have made the judgment that the units are stable,” says Naohiro Masuda, TEPCO’s chief decommissioning officer for Daiichi.

Completely cleaning up and taking apart the plant could take a generation or more, and comes with a hefty price tag. In 2016 the government increased its cost estimate to about $75.7 billion, part of the overall Fukushima disaster price tag of $202.5 billion. The Japan Center for Economic Research, a private think tank, said the cleanup costs could mount to some $470 billion to $660 billion, however.

Under a government roadmap, TEPCO hopes to finish the job in 30 to 40 years. But some experts say even that could be an underestimate. “In general, estimates of work involving decontamination and disposal of nuclear materials are underestimated by decades,” says Rod Ewing, a professor of nuclear security and geological sciences at Stanford University. “I think that we have to expect that the job will extend beyond the estimated time.”

The considerable time and expense are due to the cleanup being a veritable hydra that involves unprecedented engineering. TEPCO and its many contractors will be focusing on several battlefronts.

Water is being deliberately circulated through each reactor every day to cool the fuel within—but the plant lies on a slope, and water from precipitation keeps flowing into the buildings as well. Workers built an elaborate scrubbing system that removes cesium, strontium and dozens of other radioactive particles from the water; some of it is recirculated into the reactors, and some goes into row upon row of giant tanks at the site. There’s about one million tons of water kept in 1,000 tanks and the volume grows by 100 tons a day, down from 400 tons four years ago.

To keep more water from seeping into the ground and being tainted, more than 90 percent of the site has been paved. A series of drains and underground barriers—including a $325-million* supposedly impermeable “wall” of frozen soil—was also constructed to keep water from flowing into the reactors and the ocean. These have not worked as well as expected, though, especially during typhoons when precipitation spikes, so groundwater continues to be contaminated.

Despite the fact contaminated water was dumped into the sea after the disaster, studies by Japanese and foreign labs have shown radioactive cesium in fish caught in the region has fallen and is now within Japan’s food safety limits. TEPCO will not say when it will decide what to do with all the stored water, because dumping it in the ocean again would invite censure at home and abroad—but there are worries that another powerful quake could cause it to slosh out of the tanks.

Fuel Mop-up

A second major issue at Fukushima is how to handle the fuel¾the melted uranium cores as well as spent and unused fuel rods stored at the reactors. Using robotic probes and 3-D imaging with muons (a type of subatomic particle), workers have found pebbly deposits and debris at various areas inside the primary containment vessels in the three of the plant’s reactor units. These highly radioactive remains are thought to be melted fuel as well as supporting structures. TEPCO has not yet worked out how it can remove the remains, but it wants to start the job in 2021. There are few precedents for the task. Lake Barrett—director of the Three Mile Island nuclear plant during its decommissioning after a partial meltdown at the Middletown, Pa., facility in 1979—says TEPCO will use robots to remotely dig out the melted fuel and store it in canisters on-site before shipping to its final disposal spot. “This is similar to what we did at Three Mile Island, just much larger and with much more sophisticated engineering because their damage is greater than ours was,” Barrett says. “So although the work is technically much more challenging than ours was, Japan has excellent technological capabilities, and worldwide robotic technology has advanced tremendously in the last 30-plus years.”

Shaun Burnie, senior nuclear specialist with Greenpeace Germany, doubts the ambitious cleanup effort can be completed in the time cited, and questions whether the radioactivity can be completely contained. Until TEPCO can verify the conditions of the molten fuel, he says, “there can be no confirmation of what impact and damage the material has had” on the various components of the reactors—and therefore how radiation might leak into the environment in the future.

Although the utility managed to safely remove all 1,533 fuel bundles from the plant’s unit No. 4 reactor by December 2014, it still has to do the same for the hundreds of rods stored at the other three units. This involves clearing rubble, installing shields, dismantling the building roofs, and setting up platforms and special rooftop equipment to remove the rods. Last month a 55-ton dome roof was installed on unit No. 3 to facilitate the safe removal of the 533 fuel bundles that remain in a storage pool there. Whereas removal should begin at No. 3 sometime before April 2019, the fuel at units No. 1 and 2 will not be ready for transfer before 2023, according to TEPCO. And just where all the fuel and other radioactive solid debris on the site will be stored or disposed of long-term has yet to be decided; last month the site’s ninth solid waste storage building, with a capacity of about 61,000 cubic meters, went into operation.

As for what the site itself might look like decades from now, cleanup officials refuse to say. But they are quick to differentiate it from the sarcophagus-style containment of the 1986 Chernobyl catastrophe in the Soviet Union, in what is now Ukraine. Whereas the Chernobyl plant is sealed off and the surrounding area remains off-limits except for brief visits—leaving behind several ghost towns—Japanese officials want as many areas as possible around the Daiichi site to eventually be habitable again.

“To accelerate reconstruction and rebuilding of Fukushima as a region, and the lives of locals, the key is to reduce the mid- and long-term risk,” says Satoru Toyomoto, director for international issues at the Ministry of Economy, Trade and Industry’s Nuclear Accident Response Office. “In that regard, keeping debris on the premises without approval is not an option.” ”

by Tim Hornyak, Scientific American

source

Advertisements

High-priced Fukushima ice wall nears completion, but effectiveness doubtful — The Mainichi

” A subterranean ice wall surrounding the nuclear reactors at the stricken Fukushima No. 1 Nuclear Power Plant to block groundwater from flowing in and out of the plant buildings has approached completion.

Initially, the ice wall was lauded as a trump card in controlling radioactively contaminated water at the plant in Fukushima Prefecture, which was crippled by meltdowns in the wake of the March 2011 Great East Japan Earthquake and tsunami. But while 34.5 billion yen from government coffers has already been invested in the wall, doubts remain about its effectiveness. Meanwhile, the issue of water contamination looms over decommissioning work.

In a news conference at the end of July, Naohiro Masuda, president and chief decommissioning officer of Fukushima Daiichi Decontamination & Decommissioning Engineering Co., stated, “We feel that the ice wall is becoming quite effective.” However, he had no articulate answer when pressed for concrete details, stating, “I can’t say how effective.”

The ice wall is created by circulating a coolant with a temperature of minus 30 degrees Celsius through 1,568 pipes that extend to a depth of 30 meters below the surface around the plant’s reactors. The soil around the pipes freezes to form a wall, which is supposed to stop groundwater from flowing into the reactor buildings where it becomes contaminated. A total of 260,000 people have worked on creating the wall. The plant’s operator, Tokyo Electric Power Co. (TEPCO) began freezing soil in March last year, and as of Aug. 15, at least 99 percent of the wall had been completed, leaving just a 7-meter section to be frozen.

Soon after the outbreak of the nuclear disaster, about 400 tons of contaminated water was being produced each day. That figure has now dropped to roughly 130 tons. This is largely due to the introduction of a subdrain system in which water is drawn from about 40 wells around the reactor buildings. As for the ice wall, TEPCO has not provided any concrete information on its effectiveness. An official of the Secretariat of the Nuclear Regulation Authority (NRA) commented, “The subdrain performs the primary role, and the ice wall will probably be effective enough to supplement that.” This indicates that officials have largely backtracked from their designation of the ice wall as an effective means of battling contaminated water, and suggests there is unlikely to be a dramatic decrease in the amount of decontaminated groundwater once the ice wall is fully operational.

TEPCO ordered construction of the ice wall in May 2013 as one of several plans proposed by major construction firms that was selected by the government’s Committee on Countermeasures for Contaminated Water Treatment. In autumn of that year Tokyo was bidding to host the 2020 Olympic and Paralympic Games, and the government sought to come to the fore and underscore its measures to deal with contaminated water on the global stage.

Using taxpayers’ money to cover an incident at a private company raised the possibility of a public backlash. But one official connected with the Committee on Countermeasures for Contaminated Water Treatment commented, “It was accepted that public funds could be spent if those funds were for the ice wall, which was a challenging project that had not been undertaken before.” Small-scale ice walls had been created in the past, but the scale of this one — extending 1.5 kilometers and taking years to complete — was unprecedented.

At first, the government and TEPCO explained that an ice wall could be created more quickly than a wall of clay and other barriers, and that if anything went wrong, the wall could be melted, returning the soil to its original state. However, fears emerged that if the level of groundwater around the reactor buildings drops as a result of the ice wall blocking the groundwater, then tainted water inside the reactor buildings could end up at a higher level, causing it to leak outside the building. Officials decided to freeze the soil in stages to measure the effects and effectiveness of the ice wall. As a result, full-scale operation of the wall — originally slated for fiscal 2015 — has been significantly delayed.

Furthermore, during screening by the NRA, which had approved the project, experts raised doubts about how effective the ice wall would be in blocking groundwater. The ironic reason for approving its full-scale operation, in the words of NRA acting head Toyoshi Fuketa, was that, “It has not been effective in blocking water, so we can go ahead with freezing with peace of mind” — without worrying that the level of groundwater surrounding the reactor buildings will decrease, causing the contaminated water inside to flow out.

Maintaining the ice wall will cost over a billion yen a year, and the radiation exposure of workers involved in its maintenance is high. Meanwhile, there are no immediate prospects of being able to repair the basement damage in the reactor buildings at the crippled nuclear plant.

Nagoya University professor emeritus Akira Asaoka commented, “The way things stand, we’ll have to keep maintaining an ice wall that isn’t very effective. We should consider a different type of wall.”

In the meantime, TEPCO continues to be plagued over what to do with treated water at the plant. Tainted water is treated using TEPCO’s multi-nuclide removal equipment to remove 62 types of radioactive substances, but in principle, tritium cannot be removed during this process. Tritium is produced in nature through cosmic rays, and nuclear facilities around the world release it into the sea. The NRA takes the view that there is no problem with releasing treated water into the sea, but there is strong resistance to such a move, mainly from local fishing workers who are concerned about consumer fears that could damage their businesses. TEPCO has built tanks on the grounds of the Fukushima No. 1 plant to hold treated water, and the amount they hold is approaching 800,000 metric tons.

In mid-July, TEPCO Chairman Takashi Kawamura said in an interview with several news organizations that a decision to release the treated water into the sea had “already been made.” A Kyodo News report on his comment stirred a backlash from members of the fishing industry. TEPCO responded with an explanation that the chairman was not stating a course of action, but was merely agreeing with the view of the NRA that there were no problems scientifically with releasing the treated water. However, the anger from his comment has not subsided.

Critical opinions emerged in a subsequent meeting that the Ministry of Economy, Trade and Industry held in the Fukushima Prefecture city of Iwaki at the end of July regarding the decontamination of reactors and the handling of contaminated water. It was pointed out that prefectural residents had united to combat consumer fears and that they wanted officials to act with care. One participant asked whether the TEPCO chairman really knew about Fukushima.

The ministry has been considering ways to handle the treated water, setting up a committee in November last year that includes experts on risk evaluation and sociology. As of Aug. 15, five meetings had been held, but officials have yet to converge on a single opinion. “It’s not that easy for us to say, ‘Please let us release it.’ It will probably take some time to reach a conclusion,” a government official commented. “

by The Mainichi

source

Fukushima cleanup chief urges better use of probe robot — The Seattle Times

” TOKYO (AP) — The head of decommissioning for the damaged Fukushima nuclear plant said Thursday that more creativity is needed in developing robots to locate and assess the condition of melted fuel rods.

A robot sent inside the Unit 2 containment vessel last month could not reach as close to the core area as was hoped for because it was blocked by deposits, believed to be a mixture of melted fuel and broken pieces of structures inside. Naohiro Masuda, president of Fukushima Dai-ichi Decommissioning, said he wants another probe sent in before deciding on methods to remove the reactor’s debris.

Unit 2 is one of the Fukushima reactors that melted down following the 2011 earthquake and tsunami.

The plant’s operator, Tokyo Electric Power Co., needs to know the melted fuel’s exact location as well as structural damage in each of the three wrecked reactors to figure out the best and safest ways to remove the fuel. Probes must rely on remote-controlled robots because radiation levels are too high for humans to survive.

Despite the incomplete probe missions, officials have said they want to stick to their schedule to determine the removal methods this summer and start work in 2021.

Earlier probes have suggested worse-than-anticipated challenges for the plant’s cleanup, which is expected to take decades. During the Unit 2 probe in early February, the “scorpion” robot crawler stalled after its total radiation exposure reached its limit in two hours, one-fifth of what was anticipated.

“We should think out of the box so we can examine the bottom of the core and how melted fuel debris spread out,” Masuda told reporters.

Probes are also being planned for the other two reactors. A tiny waterproof robot will be sent into Unit 1 in coming weeks, while experts are still trying to figure out a way to access the badly damaged Unit 3.

TEPCO is struggling with the plant’s decommissioning. The 2011 meltdown forced tens of thousands of nearby residents to evacuate their homes, and many have still not been able to return home due to high radiation levels.

Cleanup of communities outside of the plant is also a challenge. The cost has reportedly almost doubled to 4 trillion yen ($35 billion) from an earlier estimate. On Thursday, police arrested an Environment Ministry employee for allegedly taking bribes from a local construction firm president, media reports said. ”

by Mari Yamaguchi, The Associated Press

source

Japan tsunami highlights Fukushima nuclear plant vulnerability — Voice of America

” The 7.4 magnitude earthquake and small tsunami that struck Japan’s northeast coast on Tuesday morning tested the sea wall constructed around the Fukushima nuclear plant, that was the site of one of the worst nuclear catastrophes in history.

The earthquake hit at early morning and was centered off the coast of the Fukushima Prefecture at a depth of about 10 kilometers, according to the Japan Meteorological Agency.

The Pacific Tsunami Warning Center said the first wave of the tsunami was measured at 90 centimeters, then the waves died down. About an hour and a half after the earthquake there was also 1.4 meter wave that was large enough to cause some flooding.

Japanese television showed tsunami waves flowing up rivers in some areas, and some fishing boats were overturned in the port of Higashi-Matsushima.

Reports of injuries and damage from Tuesday’s earthquake and tsunami were minimal. Residents in the region evacuated to higher ground after tsunami warning sirens sounded in the early morning and many ships moved out to sea to ride out the incoming ocean surge.

Magnitude

While the Japan Meteorological Agency calculated the earthquake’s magnitude at 7.4, the U.S. Geological Survey (USGS) measured it to be a 6.9 quake.

Tuesday’s earthquake was much less powerful than the 9.0 earthquake that struck the same region in March of 2011, generating enormous tsunami waves, some as high a 40 meters, that killed close to 20,000 people and caused the meltdown of the Fukushima Nuclear Power Plant, the worst nuclear crisis since Chernobyl a quarter of a century earlier.

Geophysicist Rafael Abreu with the USGS Earthquake Information Center says a one magnitude point rise on the seismic scale equals a 32 time increase in destructive power released during an earthquake.

“The magnitude of a 9.0 quake is an earthquake that released 32×32, over 1,000 times more energy then the quake that we had today,” said Abreu.

Fukushima

The Fukushima nuclear reactors that were damaged during the 2011 meltdown have been since shut down, but the Tokyo Electric Power Company (TEPCO) still maintains cooling systems to prevent the spent nuclear material from overheating and spewing radioactive waste into the air and ocean.

Naohiro Masuda, head of TEPCO’s Decommissioning Unit, said on Tuesday a one-meter tsunami was observed from two Fukushima nuclear power plants but precautions were taken to prevent a possible breech.

“With regards to Fukushima plant No. 1, it appears to be there is no problem inthe plant, but we proactively stopped operation of the contaminated water discharge system with a judgement that it could be problematic if it (radioactive water) leaks out,” he said.

In 2015, TEPCO competed a 780-meter coastal sea wall around the heavily damaged reactor buildings of the Fukushima No. 1 plant to reduce the amount of contaminated water flowing into the ocean. During the worst of the crisis it was leaking 400 tons of radioactive water a day.

An ice wall has also been constructed to reduce the amount of water flowing into the nuclear plant from the nearby mountains.

Kendra Olrich, a Senior Global Energy Campaigner with the environmentalist organization Greenpeace in Japan, said the sea wall fared relatively well this time but Tuesday’s earthquake illustrates that Japan is too geologically unstable to safely operate nuclear power plants.

“All of these earthquakes continue to highlight the absurdity of having nuclear power in a country that is sitting on the Pacific ring of fire,” she said.

Inside the damaged Fukushima plants, efforts are still underway to remove the molten nuclear core and move the highly radioactive materials to a safer storage facility.

Olrich said radioactive contamination that seeped into the surrounding forests during the tsunami five years ago continue to pose a danger to public health and safety. She is also critical of government plans to lift evacuation orders in affected areas next year that would end TEPCO’s obligation to provide compensation, at the cost of potentially exposing residents to increased risks. ”

by Brian Padden; contributions from Youmi Kim

source

Tepco admits success of Fukushima ice wall still unknown — The Japan Times

” Tokyo Electric Power Holdings Inc. and the government bet big on an underground ice wall as a key measure to battle the tainted water issue at the crippled Fukushima No. 1 nuclear plant.

But whether the ¥35 billion gambit funded by the government is working to block the inflow of groundwater remains unclear even six months after the utility started freezing an area of underground soil.

Tepco said it needs more time to judge whether the system is working. But the Nuclear Regulation Authority, Japan’s nuclear watchdog, appears skeptical on the effectiveness of the 1.5-km-long wall that encircles reactor buildings 1 to 4, asking Tepco to deal with the issue but without counting on it.

So far Tepco has finished freezing the east side of the ice wall — albeit with delays caused by severe typhoon-driven rains — and 95 percent of the west side but has yet to get the NRA’s approval to freeze the rest of it.

“It’s really unfortunate and I am very sorry” for not being able to provide an assessment of the ice wall, Naohiro Masuda, who heads Tepco’s decommissioning project, told a news conference Thursday.

Masuda said in August that Tepco would be able to provide an assessment of the effectiveness of the ice wall in September, and that the utility would have finished freezing the east side by then.

But Masuda said unexpected heavy rain during recent typhoons melted some parts of the structure.

Masuda said workers have since repaired the damage and finished freezing the east side 100 percent. But he declined to say when the assessment will be released.

The purpose of the ice wall is to block groundwater before it can enter the reactor buildings, which are located between nearby mountains and the ocean.

To do this, Tepco pumps groundwater that has flowed west to east toward five wells near the ocean, back into the reactors to cool them.

If the wall succeeds, the water being pumped from the ocean wells should reduce to about 70 tons each day, from hundreds of tons, according to Tepco. The daily level was between 600-1,200 tons in September, which Tepco attributed to heavy rains.

About 180 tons of groundwater a day seeps into the reactor buildings through cracks or holes and is mixed with contaminated water inside, causing the amount of tainted water at the plant to increase daily.

Currently, about 68,000 tons of tainted water is stored there but the risk remains that it could leak if another powerful quake hits near the facility.

For Tepco, the success of the ice wall is fundamental to achieve its next major goal of removing the contaminated water flooding the basement floors of the reactor buildings.

The utility plans to remove the water by 2020, but believes it can speed up the process by two years if the underground wall works.

The NRA, however, remains unconvinced.

“(Tepco) needs to come up with measures that do not rely on the ice wall and complete the removal of the tainted water from the building by 2020,” Toyoshi Fuketa, deputy NRA chairman, told Tepco officials at a panel meeting Wednesday.

During the meeting, Tepco expressed its intention to freeze the entire west side of the wall.

But Fuketa said, “That’s out of discussion,” since it was still unclear whether the east side was effectively blocking groundwater.

Among the NRA’s concerns is that completely blocking the groundwater on the west side might reduce the groundwater level below the tainted flooded water line in the reactor buildings, which would allow tainted water to leak out.

But as the wall appears to have done little to reduce the amount of groundwater pumped daily, the NRA ordered Tepco to come up with alternative measures.

The NRA has suggested that Tepco strengthen the pumping capability of wells around the reactor buildings to collect the groundwater before it can seep inside.

Tepco said at the Wednesday meeting that it will still be able to finish the removal of tainted water in the buildings by 2020 without the ice wall. ”

by Kazuaki Nagata

source

Tepco’s two tales about Fukushima missing melted fuel — SimplyInfo

Read SimplyInfo’s article on where the melted fuel in Fukushima No. 1’s Units 1, 2, and 3 might be, despite vague and omitting statements given by decommissioning chief Naohiro Masuda.