Simply removing contaminated material such as topsoil, however, creates a large amount of waste that cannot be made safe and will still need to be disposed of. Removing local topsoil concentrates contaminated material and makes remediation more manageable. The problem of waste disposal becomes more tractable if the radioactivity can be concentrated into a smaller volume of material. Yoshiharu Mitoma from the Prefectural University of Hiroshima, Japan, and his co-workers have developed an innovative set of techniques for immobilising and separating caesium in soil samples that is being applied to large volumes.
Immobilising radionuclides involves trapping them within a solid matrix of for example polymer or ceramic so that it can no longer be leached out of the soil. Any isotope of caesium, whether radioactive or stable, will preferentially adhere to the surfaces of soil and other organic particles. A simple strategy for decontaminating soils could therefore just involve removing the smallest particles with the highest surface to volume ratios, and therefore the highest caesium concentration.
This is a mixture of nanoscale particles of metallic calcium and calcium oxide, sometimes with the addition of metallic iron. Grinding a mixture of soil and nano-calcium both reduces the size of the soil particles and coats each one with nano-calcium, immobilising the caesium in a layer below the particles. This produces a dry sample that can be separated by particle size at room temperature. If the nano-calcium used contains iron or another paramagnetic material, this separation can be achieved through a balance of magnetic forces and gravity.
The coated particles are placed in water underneath a strong magnet, and the smallest particles — those with the highest concentrations of caesium — are attracted to the magnet even against gravity. Much of the area around Fukushima was cultivated land, and much attention has been focused on the accumulation of radiation in foodstuffs and associated health risks.
Radionuclide concentrations may therefore be unacceptably high in plants and fungi grown even in mildly affected areas. Some species of edible mushrooms are very efficient hyper-accumulators; the study of radionuclide accumulation in fungi dates back to the s, but became more urgent after the Chernobyl disaster, particularly since wild mushrooms are appreciated as a delicacy in much of eastern Europe.
Fungi can be hyper-accumulators radionuclides, making them potentially dangerous to eat. Different fungal species accumulate different metals at different rates; in particular, saprotrophs, which obtain their nutrients from dead or decaying matter in the topsoil, accumulate more quickly and take less time to reach peak concentrations than the mycorrhizal fungi that are associated with the roots of plants. Contamination of edible saprotrophs is no longer considered a problem in Europe, but it has become one in Japan.
Olivier Daillant of the Observatoire Mycologique in Mazille, France, has studied radiation in fungi since the s, and he has explored the extent to which usual cooking methods will remove the accumulated caesium. The release of much of the radiation from Fukushima into the ocean has posed a different set of problems. Again, except in the immediate aftermath of the disaster, Cs has been the main cause for concern.
Caesium — an alkali metal, like sodium — dissolves in sea water and is carried across the ocean by its currents. It is taken up by, and accumulates in, many species of edible fish. But radiation was present in the ocean before the Fukushima disaster, just as it will be centuries into the future. Besides some natural background radiation, traces of Cs can be detected left over from — for example — nuclear weapons testing in the s and 60s in the Pacific Ocean, and the Sellafield nuclear reactor near the coast of the Irish Sea.
Buesseler and his colleagues began to collect and measure radiation in samples of seawater and in fish in the Pacific Ocean between the coasts of Japan and Hawaii in the months after the Fukushima disaster, in collaboration with Japanese colleagues. Much of the radioactivity from Fukushima ended up in the ocean, where it can contaminate fish. In order to track radiation from different sources and, where necessary, to reassure the public, it is necessary to measure it very precisely.
Although the company admitted to having been aware of the radioactive water since spring of , it was not disclosed until February of this year.
This announcement further outraged local commercial fishermen, increasing the levels of distrust felt towards TEPCO [18] and the Japanese government. It has been over four years since the reactor accident. The first phase of the plan, intended to take place in the three months following the accident, described how workers would continue to flood the nuclear fuel containers with fresh water; they would also inject nitrogen gas into the reactors in order to prevent hydrogen explosions.
Next, the plan stipulated that the company would spray a plastic emulsion to prevent the dispersal of radioactive dust, and the company would used radio controlled equipment in order to remove contaminated debris. Later in , the company announced a new roadmap of reconstruction, with a time frame of over 50 years. This plan included removing fuel from spent fuel pools and completing decontamination and debris removal.
TEPCO has recently tried using robots to aid in the plant decommissioning process, but this tactic has not been as successful as hoped as the robots can only function amid high levels of radiation for two to three days. Additionally, the process requires large numbers of bodies able and willing to work in areas with high levels of radiation and contamination. As of October of , more than 50, workers had been hired to shut down the plant and decontaminate the town and villages nearby that had been affected by radiation; [24] however, there is a threshold of radiation that each individual can be exposed to, and once that limit is reached, the worker is dismissed.
Additionally, the company has a history of using subcontractors to hire workers; when they arrive at the plant, the employees are unaware that they will be working in areas with high levels of radiation, as they are told they will be clearing debris from the tsunami. As one former employee states in the video below, the company lies about the safety of the job and the workers are tricked into working a job they are unprepared for.
Although TEPCO and the Japanese government have made strides in the decontamination and restoration processes, at times it seems as if their efforts are for naught. In addition, many of the families that had been forced to evacuate after the accident are unwilling to move back to their homes, begging the question of is the decontamination process even worth it? In the days that followed the quake, the Fukushima-Daiichi plant was rocked by hydrogen explosions, which burst through the roofs of the three afflicted reactors, sending radioactive iodine, cesium and other fission by-products belching into the environment.
Millions of liters of water were pumped from the ocean to cool the overheating reactors, cascading contamination into the sea. A clock, found in debris on a beach in Fukushima, stopped at the exact time the March 11, tsunami hit.
Officials with Tokyo Electrical Power Co, or Tepco, say that the excess water they have collected must be disposed of so they can build facilities they need to begin the retrieval of radioactive debris within the reactors. That wreckage is slated for removal by December Remote control cranes are being used to dismantle the cooling tower of the No 2 reactor, the first from which molten nuclear fuel was removed.
As the Associated Press reported, most above ground areas at the Fukushima plant can now be visited with minimal protective gear and a Geiger counter. The radioactive remains of the reactor buildings are, however, still off limits. But areas underground beneath the plant remain extremely hazardous.
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