The Fukushima Cleanup Will Take GenerationsPolitics Economy Science Technology Society
The Tōhoku tsunami of March 11, 2011, triggered a series of equipment failures leading to multiple meltdowns, explosions, and releases of radioactive material at the Fukushima Daiichi Nuclear Power Station, operated by Tokyo Electric Power Company. Five years after the second-worst nuclear accident in history (after Chernobyl), the cleanup team is still struggling to halt the buildup of contaminated water, and the techniques and equipment needed to locate, extract, and dispose of the melted fuel have yet to be developed. Given these challenges, many experts are convinced that the decommissioning process will take far longer than the official 40-year timetable—perhaps as long as a century.
A Five-Year Battle Against Groundwater
One of the first things a visitor will notice upon entering the site is row upon row of massive cylindrical water tanks. Built to store some 800,000 tons of radioactive water, these 1,100 or so tanks bear witness to the epic battle that has absorbed the energies of the cleanup team for the past five years, as it struggled to contain and decontaminate radioactive water and halt its accumulation.
Rainwater and groundwater have continued to pour into the damaged basements of Units 1–4, where it mixes with the highly radioactive cooling water already inside the buildings. To stem the buildup of this contaminated water and prevent it from flowing into the ocean, TEPCO has devised a complicated patchwork of strategies aimed at solving the problem by 2020.
The pillars of TEPCO’s water management efforts to date are two systems for channeling groundwater away from the contaminated basements and releasing it into the ocean relatively free of radioactive contaminants. One, the groundwater bypass system, collects water in wells dug between the reactor buildings and the hills to the west. The water is pumped up from the wells, tested, and eventually released into the ocean. The other, called the subdrain system, uses wells dug around the perimeter of the reactor buildings. So far, TEPCO has discharged some 230,000 tons of water into the ocean using these two methods combined. Even so, groundwater continues to pour into the buildings' basements at the rate of about 150 tons a day.
Some steps TEPCO has taken have generated new problems. An example is the “sea-side impermeable wall” built by sinking close to 600 cylindrical steel piles—each about 30 meters long and a little more than 1 meter in diameter—into the seabed along the waterfront. In October 2015, TEPCO completed the 780-meter barrier. However, the water pumped from the area inside the wall was found to be too radioactive to be released, and as the groundwater level rose, TEPCO was forced to pump it back into the basement of the turbine buildings at the rate of about 550 tons a day. Thus the expensive project has actually exacerbated the accumulation of contaminated water instead of mitigating it, and so far there is no solution to the problem in sight. TEPCO has also installed equipment around the reactor buildings for the purpose of creating an “ice wall” of frozen soil to block the influx of groundwater, but it could be another eight months before the wall is complete.
At a September 2013 meeting of the International Olympic Committee, shortly before Tokyo was selected to host the 2020 Summer Olympics, Prime Minister Abe Shinzō disposed of water-contamination concerns with a breezy “Let me assure you the situation is under control.” This was certainly not the case then, in the wake of revelations that 300 tons of highly radioactive water had leaked into the ground from a storage tank. Today, five years after the 2011 accident, the problem of contaminated water remains a serious challenge. But from a crisis-management standpoint, it is probably fair to say that the situation is finally under control.
Improvements in Working Conditions
Working conditions for the plant’s cleanup workers—who number in the thousands—have improved dramatically over the past few years. Perhaps the most important change in this regard has been the drop in the radiation levels to which workers are routinely exposed. By the end of March 2016, TEPCO expects to meet its target of reducing the effective radiation exposure at the site boundary to less than 1 millisievert per year above natural background levels—about a tenth of the level recorded back when accident debris and the highly radioactive water in storage tanks were still contaminating the air.
One way that TEPCO is reducing radiation exposure at the site is by paving the grounds. The plan, now about 85% complete, is to pave 1.45 million square meters out of the total area of 3.5 million m2. Meanwhile, much of the radioactive water stored in above-ground tanks has undergone initial treatment using advanced liquid processing equipment and other filtration systems.
Thanks to such measures, except for the immediate vicinity of the stricken reactors (where the radiation dose can still be higher than 100 mSv per hour), most of the site is now safe to walk through with no more than a coverall and disposable dust mask for protection. Working at Fukushima Daiichi is no longer a high-risk job, provided one has the sense not to wander unprotected into the radioactive zone around the crippled reactors.
When I visited recently, the work atmosphere was surprisingly pleasant and relaxed. In the cafeteria, employees smiled and laughed easily as they chatted over lunch. The second-floor dining room is part of the nine-story employee “rest house” near the plant’s west entrance. The building, completed in June 2015, features lounges and other common areas along with the cafeteria, which offers a choice of noodles and other hot meals (prepared offsite) at a price of just ¥380. This is another area of dramatic improvement from the early days, when cleanup workers were provided with no more than a bottle of mineral water and some crackers.
“It’s important to make the compound as much like a normal work site as possible,” explained Masuda Naohiro, chief decommissioning officer. Masuda is president of Fukushima Daiichi D&D Engineering Company, set up in April 2014 to “provide optimal focus, expertise, and efficiency” and “clarify the lines of responsibility within TEPCO.”
A red fox made a cameo appearance during my visit to the plant. The creature made no move to flee even when we passed fairly close, and the workers walked on smiling, apparently accustomed to the sight. The almost incongruously pastoral image struck me as another sign of the substantial progress TEPCO has made in improving overall conditions and reducing stress levels at the site of the 2011 accident.
Challenges of Fuel Removal
At the heart of the decommissioning process, however, is the monumental challenge of extracting the reactors’ nuclear fuel. And from a practical standpoint, this process has barely begun. No human being can safely enter the reactor buildings owing to extremely high radiation levels. There is no precedent anywhere in the world for dismantling reactors under these conditions. At this stage, the team is still searching for answers to the most basic questions: What is the state and location of the melted fuel? What sort of technology is needed to extract it?
Since all six of the reactors at Fukushima Daiichi are to be scrapped, the decommissioning team plans to make use of Units 5 and 6, which suffered little or no damage, as testing facilities for the decommissioning of Units 1–3. Unit 4 also escaped meltdown, as it was offline for a scheduled safety inspection when the disaster struck. For this reason it presents fewer challenges to decommissioning than Units 1, 2, and 3, but it is also a lower priority.
The first objective is removal of the spent fuel stored in each unit’s spent-fuel pool, located near the top of the reactor building—a procedure performed periodically at normally operating nuclear power plants. At Unit 4, the last of 1,535 assemblies were successfully removed in 2014. At Units 1–3, however, the job is greatly complicated by structural damage and high levels of radioactivity.
At Unit 1, where a hydrogen explosion ripped through the roof in March 2011, a temporary cover was installed early on to prevent further dispersal of radioactive matter. TEPCO must dismantle that cover and clean up the debris beneath it before it can start removing fuel from the spent-fuel pool. In October last year, it finished removing the top panels from the cover. Next, it will remove the side panels and install windscreens to prevent the wind from stirring up radioactive dust. Then it will begin removing debris from the upper section of the reactor building through the open roof. The removal of fuel from the spent-fuel pool is not expected to begin until 2020.
By the summer of 2016, the team hopes to begin dismantling the uppermost section of the Unit 2 building. Unlike Units 1, 3, and 4, whose outer shells were damaged or destroyed by hydrogen explosions, Unit 2 remains outwardly intact. But since the building and its fuel-handling equipment were all contaminated by intense radiation from within, the entire top section must be dismantled to make way for new cranes and other equipment to remove the fuel. The plan is to remove all structural elements above the service floor to gain clear access to the spent-fuel pool, with fuel removal scheduled to begin in 2020.
At Unit 3, a huge hydrogen explosion demolished the entire top portion of the building, leaving tons of rubble in and around the exposed spent-fuel pool. The team has finally finished removing steel beams, concrete slabs, and other large pieces of wreckage and can now turn its attention to vacuuming up and cutting away smaller pieces of debris and decontaminating the floor. The next step is to install a special cover over the service floor, along with a fuel-handing system to remove the 566 fuel assemblies in the spent-fuel pool. Fabrication of the cover and installation training are nearing completion in Iwaki, 50 kilometers to the south. Installation is expected to begin during the first half of 2016, and fuel removal is scheduled to commence sometime in 2017.
TEPCO is still working to determine the location and state of the fuel that was inside the reactors at the time of the accident. Sometime this year, it hopes to send a camera-equipped robot probe into Unit 1 to capture images of the melted fuel believed to have fallen out of the reactor core and into the bottom of the primary containment vessel (PCV). Similar probes of Unit 2 and 3 are expected to get underway sometime in 2016 and 2017 respectively.
The fundamental reason for this slow progress is the extremely high level of radiation inside the containment vessels. Although remote-controlled robots have been used for preliminary surveys, precision equipment cannot withstand the intense radioactivity near the fuel debris, the source of the radiation. At Unit 1, the team is hoping to circumvent this problem with a camera suspended from a robot by a long cable. Some of the nation’s top engineers are working on the development of radiation-resistant robots for the cleanup, but that will take time.
Give It a Century or So
Of course, ascertaining the state and location of the melted fuel is not the same as extracting it. How does one remove molten radioactive fuel from the containment vessels?
One oft-mentioned possibility is to fill the PCVs with water and then use some as-yet undeveloped equipment to extract the solidified debris. But will the damaged vessels be able to hold water? According to Madarame Haruki, who served as chairman of the old Nuclear Safety Commission, “It’s going to be very difficult to prevent the water from leaking out of the containment vessels, and if they can’t fill them with water, then it’s hard to see how they can use a robot to remove the fuel.” Moreover, even if they can somehow repair the vessels and fill them with water, they will need to find a way of breaking up fuel that has congealed into a solid mass. Then there is the problem of storing the fuel after extraction.
Even without melted cores and damaged containment structures to contend with, decommissioning a nuclear reactor can take decades. The complete dismantling of Units 1 and 2 at the Mihama nuclear power plant in Fukui Prefecture (which Kansai Electric recently decided to retire for reasons of age and cost) is expected to take 30 years. The estimate for Unit 1 at the Tsuruga nuclear plant (Japan Atomic Power Company) is 25 years. As for decommissioning the reactors at Fukushima Daiichi, Madarame says, “It could probably be completed in a century or so.”
The 40-year timetable issued by TEPCO and the government is based on little more than highly optimistic guesswork. Only when the team has a clear picture of the state and location of the reactors’ nuclear fuel will they be able to draw up a realistic roadmap for decommissioning.
That being the case, we should not be surprised if the authorities release a drastically revised timetable in the not-too-distant future. And when that happens, there will be little point in criticizing the cleanup team for the delay. The important thing in this situation is not staying on schedule but getting it right. The future of Fukushima Prefecture depends on it.(Originally written in Japanese. Article photos courtesy of the author. Banner photo: Tanaka Shun’ichi, chairman of Japan’s Nuclear Regulation Authority, tours TEPCO’s Fukushima Daiichi Nuclear Power Station in February 2016. © Jiji.)