Fukushima biography

Our author Julia Ipatova visited the station and found out what technologies are now used at Fukushima-1. At the forefront of this long -term project today is the creation of reliable protective barriers that will ensure the safety of everyone who participates in it. More people work at the station daily. The average annual dose of irradiation of the station employees is about 2.67 mZV per year with the maximum permissible maximum dose of 50 mZV per year.

The chronology of the events of March 11, the meter wave of Tsunami hit the Fukushima-1 NPP, flooding the lower floors of the station. In the first minutes of the accident, the backup diesel units located in the basement were flooded, which led to an automatic shutdown of three power units from power supply. Emergency batteries were enough for only a few hours.

Due to insufficient cooling, the level of the coolant began to decrease, and the steam pressure in the upper parts of the reactor continued to grow. The reactor case was not damaged, but the external reinforced concrete shell of the building was destroyed. On the same day, the zone of evacuation of residents around the nuclear power plant reached a radius of 20 km, since at the time of the hydrogen explosion radioactive substances from the waters of the fuel aging pool fell into the atmosphere.

On the night of March 16, a fire arose in the fourth power unit in the fourth power unit, which is why radioactive substances fell into the atmosphere. The consequences could be unpredictable if an uncontrolled chain reaction in the pool began for the exhaust fuel rods, but, fortunately, the fire was extinguished. As a result of the accident, more thousand were evacuated.

A strategic action plan in the Japanese legal system for nuclear accidents Tokyo Electric power company TEPCO, as a Licensee of the Station, bears unlimited responsibility for its decommissioning. Nuclear Regulatory Authority - NRA nuclear regulation controls the work and decommissioning. Corporation for the promotion of compensation for nuclear damage and decommissioning NDF is a legally authorized organization for the supervision of the TEPCO activities.

Work on the conclusion is followed by the milestones specified in the preliminary plan, which was agreed by the Japanese and Tepco government. Phase 1 - the period before the start of fuel extraction from the bargaining pools of OHS. Phase 2 - the beginning of the unloading of molten fuel of the corium. At the same time, the export from the pool of the elaborated fuel of the fourth bloc began on November 18 and ended on December 22.

Now there is an active preparation for the unloading of the corium from the first block, starting from the fence of the minimum laboratory samples for initial studies. The dismantling of roofs and wall panels, columns and beams of the building of the first power unit have already been completed. A lid will be installed above the reactor body to unload fuel and equipment safely for the environment.

Before unloading, the upper part of the operating floor of the building will also be completely dismantled. By February, a domed roof was completed to prepare the dismantling of fuel rods. Both barriers will allow you to collect infected water and prevent it from getting into the Pacific Ocean. Water collected in tanks is previously cleaned of more than 60 isotopes the main long -lived of them - strontium and cesium using a special filter improved liquid processing system Alps Advanced Liquid Processing System.

However, tritium isotope of hydrogen containing one proton and two neutrons and emitting beta radiation in this water is present. Certain technological difficulties are associated with this: the main properties of tritia, including the boiling point, are similar to the characteristics of ordinary water. Potential measures to get rid of tritius include injecting tritius into deep pockets of the Earth, a reset into the sea, forced evaporation, electrolysis and underground burial.

In order to avoid further pollution of water through underground rivers, ground and rainwater drains, which, passing through the territory of the station, can harm the planet ecosystem, numerous measures have been taken. About 1.5 thousand work was loaded to a depth of 30 meters. Work in this direction has been carried out for a long time: back in December 1.5 thousand.

On the first block, work is now underway to carefully clean and remove the crushed stone, formed over the fuel basin and representing the fragments of the roof of the reactor and the iron frame. After removal, crushed stone is stored in storage facilities of solid waste or others, depending on the level of radiation. For the second block, methods of dismantling the contaminated body are studied.

According to forecasts, its decision may take several decades. The so -called Fukushima fuel melts Fukushima Fuel Debris, or Corium, were formed during the course of emergency processes. It is planned to start work with small -scale selection of fuel samples from the first reactor; Then more global operations will follow.Particular attention will be paid to safety, they say in TEPCO, for example, atmospheric control, which allows to eliminate the entry of highly radioactive substances into the environment, control over polluted water, oxygen and hydrogen.

To extract a coryum from reactors is half the battle. An analysis of the extracted materials, fundamental studies, as well as the calculation of the behavior of the components of the corium using the example of fuel models are also needed. Fukushim’s robots are clear that people cannot penetrate the Fukushima-1 reactor heart, because the radiation dose that they will receive there is deadly.

The collection of samples of molten fuel inside the reactors will be carried out using robots. It is planned to extract samples from the most infected zones using robotics and special-controling: methods of remote internal control, remote manipulator, instrumentation. The system with remote devices should have special characteristics: durability and performance in conditions of the highest radiation background.

For comparison, a dose of 1 ZV is enough for the occurrence of acute radiation disease. For a long time, questions remained open: what happened to the fuel melts, did it remain within the reactor and where its main accumulations are concentrated? Given the difficult highly radiation conditions, it was necessary to design machines whose electronics could withstand high gamma radiation.

The new Little Sunfish robot for the underwater study of the Fukushima-1 NPP reactor is represented by Toshiba in Yokosuka initially the robots showed not the best results: aggressive radiation clogged their microprocessors and chambers, concrete walls blocked wireless signals. In the earliest models, the intensive level of radiation melted electronics. So, the promising inch robot “Scorpio”, which was developed by TEPCO for more than 2.5 years, was launched into the lower part of the 2nd block reactor in December.

But after only two hours, the clock mission “Scorpio” was planned among the fragments of molten metal was planned. Equipped with a dosimeter and a waterproof chamber, he removed the readings of radiation and digital images at ten different points. Seven months after the failure of Scorpio, in July, the Toshiba scientists achieved more success with the new submarine robot Little Sunfish: swimming a high level of radiation inside the water -filled water.

On the second intelligence day, Little Sunfish registered the first signs of molten fuel inside the reactor. In January, Toshiba returned to a heavily contaminated second block with a new car, one of the chambers of which is capable of turning and bending, as well as a panoramic camera attached to the tip of the telescopic guide pipe for a better viewing angle. As soon as the robot reached the reactor’s heart, the workers remotely lowered the panoraming chamber and tilting another 2.5 meters to take unique photos.

It became clear that in all three reactors the fuel flowed outside the housings to the bottom of the harrow. However, to understand where and in what quantity the fuel has accumulated is only the first part of the task. The most difficult thing is to extract molten fuel "cocktail". Inside the reactors there are elements of equipment, the weight of which exceeds a ton.

All these operations will be performed by robots for the first time, and it is possible that in the future these machines will be used to carry out accelerated programs to withdraw nuclear power plants. To calculate how much solid waste is formed during work on decommissioning is still unrealistic: it is still necessary to extract the Corium and dismantle the buildings.

Therefore, a well -thought -out strategy will also be required here: it is necessary to take into account the unique properties of waste, their huge volumes and high doses of radiation, as well as the complexity of the nuclear composition. All this makes it difficult to develop the final plan.

Japan is helped by colleagues from different countries. Such technological approaches are developed to study trial and final extraction of corium. US projects are related to the design of containers for storing a highly radioactive corridor collected from reactors. Russia, in turn, conducts an approximate assessment of the characteristics of fuel melts and the influence of external factors on their degradation, modeling analog fuel samples.