Catastrophe of Tchernobyl

The catastrophe of Tchernobyl , the Nuclear accident most serious ever occurred (level 7 on the INNATE), occurred the April 26th 1986 in the nuclear plant Lénine located on an affluent of the Dniepr at approximately 15 km of Tchernobyl (Ukraine) and 110 km of Kiev, close to the border with the Bielorussia.

Causes of the catastrophe

The Catastrophe of Tchernobyl results from the thermal explosion of the nuclear reactor n°4, consequence of the excessive rise in the temperature inside the tank where the bars (pencils) of are located Fuel nuclear and graphite being used as regulator. When the Chaleur produced by the engine was not evacuated any more in sufficient quantity by the cooling system, the temperature and the pressure increased on levels exceeding the value of dimensioning of the structures. The physical explosion of the heart involved the scattering around the engine and the diffusion in the atmosphere of materials constitutive of the heart in gas or solid form. This explosion was maintained thereafter by combustion graphite, present in great quantity in this type of engines.

The reactive of the explosion is the Caloporteur, in the species of light water. Heat would have caused the Radiolyse water, then the recombination of released hydrogen and oxygen would have caused the explosion which raised the concrete flagstone recovering the engine. According to other experts, the explosion would be a Explosion of vapor, leading to the same consequences. Caution: it should be noted that the explosion does not have anything nuclear power : if the starting point is well a chain nuclear reaction, it is well a chemical, and nonnuclear explosion which caused the deflagration.

Following the accident, great quantities of Radioisotope S, radioactive (and for some, extremely poisons in addition), were released in the atmosphere. The accident which occurred with the Nuclear plant of Tchernobyl in the engine number 4 is thus classified of level 7 in the scale INNATE which is used to measure the gravity of the nuclear accidents, corresponding at the highest level.

Design and construction of the engine

The engine of section 4 is of type RBMK 1000 (engine of great power to tubes of force). From its design, this type of engines present several weak points:

Its Void coefficient is positive with low power and under certain operating conditions (contrary to more recent engines RBMK): so bubbles are formed in the fluid Caloporteur, the reaction tends to pack. This irrefutable fact has the following origins

on the one hand the dominating regulator is the graphite which is solid and not very sensitive in volume to the temperature variations
on the other hand to be able to use uranium little enriched the network under operation is close to the optimum of moderation
these provisions were regarded as good by the originators because they make the network relatively not very sensitive to the variations of the rate of vacuum in the normal functioning of the engine what is a good thing from the point of view of the overall regulation of the power station since more the power is high plus pressure vapor is low and the rate of vacuum raised in the heart
in certain configurations however one can be with an overmoderated heart in which

the disappearance of hydrogen atoms regulator
the disappearance of oxygen atoms absorbents
induced by the increase in the rate of vacuum in the heart cause an increase in the reactivity

the use of the Graphite as moderating makes it flammable when the temperature increases too much.
the emergency stopping device of the engine is particularly slow (20 seconds). This emergency stopping device is ensured by moderating bars, said control rods, which go down in the heart from the engine. Moreover in certain situations the control rods are made in such way that they bring reactivity during the first phase of their descent in the heart. This irrefutable fact was a worsening factor of the accident because the operators were thus misled: they laid out without the knowledge of an accelerator and not of a brake of the chain nuclear reaction In the power stations of the same type that the French power stations, these bars go down under the only action from gravity in the event of urgency. So they put approximately 1 second to reach their maximum effectiveness.
also Let us note that the power station of Tchernobyl did not have a containment, contrary with the majority of the current power stations; it is what made it possible the radioactive rejections to escape easily in the environment.

In addition to these problems of design, the construction of the power station was carried out without respecting the standards in force. A confidential relationship of 1979, signed by the director of the KGB Iouri Andropov and quoted by Nicolas Werth, stresses that “various building sites constructing block 2 of the atomic power station of Tchernobyl undertake their work without any respect of the standards, of technologies of assembly and construction defined in the Schedule of conditions”.

In 1983, the “act of experimental introduction” of the engine n°4 of the central of Tchernobyl is signed whereas “all the checks had not been completed.” engine had been reduced of 3200 MW with 1000 MW within the framework of this test in the night from April 25th to 26th.

The accident then occurred following a series of errors made by the technicians of the power station. The operators in particular violated procedures guaranteeing the safety of the engine and thus of the power station. Lastly, since its startup in 1977, the power station is directed by Viktor Petrovitch Brioukhanov, an engineer in Thermodynamique and not a specialist in the nuclear power. It belongs to a generation of men promoted thanks to “their voluntarism militant, which consisted initially and before very filling and exceeding the plan of production, notwithstanding the respect of the construction standards or of safety. ” The two thousand tons of the concrete flagstone recovering the engine are projected in the air and fall down of skew on the heart of engine, which is fractured by the shock.

A very important Incendie is declared, while a light with the blue reflections emerges from the formed hole.

It should be noted that the technicians present on the spot, like Brioukhanov awaked with 1:30, immediately do not seize the extent of the catastrophe. This last calls the ministry for Energy to 4:00 by declaring that “the heart of the engine is probably not damaged. ”.

The smothering of the heart of the engine in fusion (April 26th - May 14th 1986)

The extinguished fire, the technicians of the power station become aware of wide damage caused by the repercussion of the roof on the engine, which from now on is fissured. Graphite always in combustion, mixed with the combustible magma of which continues to react, releases a cloud of smoke saturated with particles Radioactive S.

Thus should as fast as possible be choked the uncontrolled nuclear reaction. It is only then that the engine could be insulated by a sarcophagus.

The first operation is carried out thanks to a ballet of Hélicoptère S soldiers of transport carried out by more than thousand pilots. It is a question of releasing in the open hole of the thousands of tons of Sable, of Argile, Plomb, Bore, Borax and Dolomite, a mixture which will make it possible to stop the nuclear reaction. The mission is difficult, because it consists in releasing the bags with a height of 200 m in a hole of 10 m of diameter approximately, and this as quickly as possible, because in spite of altitude the people receive 15 Röntgen in 8 seconds (3 000 times the maximum amount tolerated per annum in France for a personne). In the only day of the April 30th, 30 tons of sand and clay are thus poured on the engine.

On the roof and in the immediate neighborhoods of the power station, about fifty operators are charged in the first days following the catastrophe to very collect the remains Radioactif S. Each operator has only 90 seconds to carry out its task. It is exposed to this occasion with extremely high radiation levels of which hardly protect it from the ridiculous protective gears, mainly intended to prevent it from inhaling radioactive dusts. Number among these workers in first line developed cancers thereafter and died in the years which followed.

However, the engine is always active and the concrete flagstone which supports it threat to fissure. More serious, the water poured by the firemen to extinguish the fire drowned the substructures, thus threatening the integrity and controls of the 3 other engines of the power station. If the heart is inserted to this pocket of water, a new explosion, much more powerful than the first (because will be then nuclear), could occur, which would involve amongst other things the destruction Kiev. A new team of firemen is then sent to evacuate this water. Those will always work without protection and will leave their life there.

Under the heart of the engine in fusion, the concrete flagstone threatens to melt. One thus brings tens of thousands of minors of the mines of the surroundings of Moscow and Donbass to dig a driving tunnel under the engine in order to dig a room there. A cooling coil to helium must be installed there to cool the concrete flagstone of the engine. The minors work under very difficult conditions due to the high temperature and the very important level of radiation (the dose rate at the exit of the tunnel is approximately 200 Röntgen per hour).

The realization of the sarcophagus and the decontamination of the zone (May 14th 1986 - December 1988)

Late evacuation of the populations

The April 26th 1986, the local population is not prevented an accident and continues its usual activities without taking special precautions. Thus in Pripiat, 900 old pupils from 10 to 17 years take part in a “marathon of the peace” which makes it tower of the power station. A silver film amateur of time shows in a very obvious way that Pripiat is already contaminated seriously: the radioactivity made there of many white flashes at the rate/rhythm of several a second.

The evacuation begins the April 27th and the 45 000 inhabitants of Pripiat are the first concerned. They were not informed a few hours before by the local radio, who asked them to carry only the strict minimum and promised to them that they would be of return under 2 or 3 days. Taken along by the army, they are lodged under precarious conditions in the area of Polesskoie, itself seriously touched by the radiations. The first Symptôme S of a strong exposure to the radiations (nausea S, Diarrhea S, etc) start to appear already at much of them.

At the beginning of May, 115 000 people living in a ray of 30 km around the site are evacuated, operation which continues until the end of August. Each evacuee receives an allowance of 4000 Rouble S by adult and 1500 roubles per child. The evacuations touch approximately 250 on the whole; 000 people of Bielorussia, Russia and Ukraine. Slavoutich, a city more cash 30 000 inhabitants with the end of the year 1987, is created Ex nihilo .

Four decreasing “zones of contamination” are defined. Two of them are not evacuated, but the inhabitants have a medical monitoring and premiums of Risque.

The administrative management and policy of the catastrophe

The opacity of the local authorities and the bureaucratic levels

In the first hours which follow the catastrophe, the opacity created by the various administrative levels is total. Mikhaïl Gorbatchev is informed officially only the April 27th. The report/ratio which is transmitted to him speaks about an explosion, death of two men, stop of sections 1,2 and 3. The reports/ratios submitted to the Soviet leader are surrounded by “a wealth of precautions oratories”. The lack of information of the more leading high authorities is certainly the consequence of the undervaluation, upon the departure, of the gravity of the catastrophe (cf supra), but also of the culture of the secrecy inherent in the Soviet system .

The role of the Western countries

The April 28th in the morning, an abnormal level of Radioactivité is noted in the Nuclear plant of Forsmark in Sweden, which involves the immediate evacuation of the whole of the site by fear of an internal radioactive escape. But the first analyzes show that the origin of the contamination is external with the power station and comes from the east. The afternoon of the same day, the Agence France-Press brings back the incident.

As from this moment, all the Hypothèse S are formulated by the Western Média S. Information arrives at the account-drop (interview with Kiev evacuated people of the zone, etc). The news agency HEAP speaks the April 29th about an accident “of average gravity to the nuclear plant of Tchernobyl” while the satellite photos of the site of the power station reveal the first images of the catastrophe.

The communication of crisis: a Soviet mixture of propaganda and an negative image of transparency

For Gorbatchev, the catastrophe constitutes the first implementation of the policy of Glasnost (“transparency”) presented during the XXVII {{E}} congress of the PCUS (February 25th - March 6th 1986) and which met strong oppositions. In its spirit, the accident constitutes “a new strong argument in favor of deep reforms. ”

The May 14th, Gorbatchev pronounces a short televised speech in which he recognizes the extent of the catastrophe and admits that major dysfunctions had as a consequence that “neither the policies, nor even the scientists were prepared to seize the significance of this event. ”

This will of Transparence does not go without a very important propaganda around work completed, intended to emphasize the “battle against the atom”. A streamer affixed on the broken engine proclaims that “the Soviet people are stronger than the atom” while a red flag is fixed at the top of the tower of ventilation of the power station at the conclusion of work of clearing.

Consequences of the catastrophe

Human and material consequences

A “sarcophagus”, made up of a part in Concrete at its base and of a metal frame on the upper parts was built by the Liquidateurs around and on the remainders of the destroyed engine. Its principal function is to protect the radioactive materials from the bad weather. It is also used to prevent the gas leaks and of radioactive dusts within reasonable limits, making it possible to carry out work in the neighborhoods of the site.

This work was completed in record time taking into account the extreme conditions of radioactivity (the sarcophagus was brought into service at the month of November 1986, that is to say only six months after the catastrophe). This exploit was made possible thanks to the massive participation of the soldiers of the Soviet army, and more largely of the whole of the valid male population of the USSR.

In addition to the evacuation of the zones which constituted a major traumatism on the populations living of the Agriculture, it is the fate of the samosioli which remains today more striking. Samosioli (or “individual French colonists”) is the name given to the people returned to live in the zone of exclusion, in spite of prohibitions, and which live in autarky of their small holding. Their number is estimated at a thousand.

See too

Nuclear energy
List of the nuclear accidents
INNATE: international scales of the nuclear events

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