The Chernobyl accident

1. The Chernobyl accident

Fulfilled:Vasilyev Ilya
Artemyev Miroslav ,
Roma, Kazachuk
pupils of 8 class The
MOB OOSH Yakutsk
2017-2018 school year

2. Briefly

The Chernobyl accident — the destruction of April 26, 1986
fourth unit of the Chernobyl nuclear power plant located on the
territory of Ukraine (then the Ukrainian SSR). The destruction
had explosive character, the reactor was completely destroyed,
and in the environment were released large quantities of
radioactive substances. The accident is regarded as the largest
of its kind in the history of nuclear power, as by prospective
quantity of victims and affected by its consequences and the
economic damage. At the time of the accident Chernobyl
nuclear power plant was the most powerful in the USSR.The
radioactive cloud from the accident passed over the European
part of the USSR, Eastern Europe and Scandinavia.
Approximately 60% of radioactive fallout landed in Belarus.
About 200,000 people were evacuated from the areas
contaminated.The Chernobyl accident was an event of great
socio-political importance for the USSR, and it left a definite
imprint on the course of the investigation[1] [2]. Approach to the
interpretation of the facts and circumstances of the accident
changed over time, and completely no consensus so far.

3. Crash

About 1:24 on 26 April 1986 at the 4th unit of the
Chernobyl nuclear power plant explosion, which
completely destroyed the reactor. The building of
the unit partially collapsed, killing 1 person
employee 4 unit Valery hodemchuk. In different
rooms and on the roof started the fire.
Subsequently the remnants of the active zone
melted. The mixture of molten metal, sand,
concrete and particles of fuel spilled on podirectory
premises.[3][4] as a result of the accident there
was an emission of radioactive substances,
including isotopes of uranium, plutonium, iodine131 (half-life 8 days), caesium-134 (half life 2
years) cesium-137 (half-life 33 years), strontium-90
(half-life 28 years). The situation was compounded
by the fact that in the destroyed reactor continued
uncontrolled nuclear and chemical (from the
burning of reserves of graphite) the reaction heat,
with the eruption from the fissure for many days
burning products of radioactive elements and their
contamination of large areas. Stop the active
eruption of radioactive substances from the
destroyed reactor could only end in may 1986.
mobilization of all resources of the USSR and the
price of mass exposure of thousands of liquidators.

4. The cause of the accident

There are at least two different approaches to explaining the causes of the Chernobyl
accident, which may be called official, as well as several alternative versions of different
degrees of reliability.Initially the blame for the disaster was laid exclusively, or almost
exclusively, on staff. This position was occupied by a State Commission, formed in the USSR
to investigate the causes of the disaster, court and KGB, who conducted his own
investigation. IAEA in its report, 1986 [9] also generally supported this view. A significant
portion of publications in the Soviet and Russian media, including recent and, based on this
version. It is based on various artistic and documentary works, including the famous book of
Grigori Medvedev's "Chernobyl notebook".Gross violations of operating nuclear power plants
committed by the personnel of the ChNPP, according to this version, was the following:the
experiment at any cost, despite changing the state of the reactor; the output from a working
process protections that just would stop the reactor before it would get dangerous mode;
silence on the scale of the accident in the first days of the ChNPP management.However, in
subsequent years, explaining the causes of the accident were reviewed, including IAEA. The
Advisory Committee on nuclear safety (INSAG) in 1993 published a new report[10], is paid
more attention to the serious problems in the reactor design. In this report, many of the
conclusions in 1986, were considered incorrect.In the modern interpretation, the cause of the
accident as follows:the reactor was improperly designed and dangerous; the staff was not
informed about the dangers; the staff made some mistakes and inadvertently breaching the
existing regulations, partly due to the lack of information about the dangers of the reactor;
disable protection or no impact on the development of the accident, or not contrary to
regulations.

5. Operator error

Initially it was claimed that the operators have committed numerous violations. In particular, the fault of
the staff raised the fact that they shut down the main protection system of the reactor, continued its work
after the fall of the power to 30 MW and the reactor is stopped, even though I knew that the operating
reactivity margin is less than allowed. It was stated that these actions were in breach of the guidelines
and procedures was the main cause of the accident.Lock protection, which stops the reactor in case of
stopping of two turbine generators, not only was allowed but was required for work at low power. What
was not included protection for low water level in the tanks-separators, technically, was a violation of the
rules. However, this violation is not directly linked to the causes of the accident and, in addition, another
defense of (at lower level) was included.Now, when analyzing the actions of the staff did not focus on
specific disorders and low "safety culture". It should be noted that this concept of experts on nuclear
safety was used only after the Chernobyl accident. The charge applies not only to operators but also to
the designers of the reactor, the plant's management, etc. Experts point out the following examples of
inadequate attention to security issues:After disconnection of the emergency core cooling (ECCS) on 25
April from the Manager "Kyivenergo" received instructions to postpone the shutdown of the unit, and the
reactor a few hours worked with disabled ECCS. Staff have not had the opportunity to lead the ECCS in
the ready state (for this I had to manually open some valves, but it would take a few hours[11]), but from
the point of view of safety culture, as it is understood now, the reactor should have stopped, despite the
requirement of "Kyivenergo". 25 APR within hours of operational reactivity margin (ORM), on
measurement, was less than allowed (in these measurements may have been an error, which the staff
knew; the real value was in the allowed range[12]). On April 26, just before the accident, ORM also
(briefly) was less than allowed. The latter was one of the main causes of the accident. IAEA experts note
that the reactor operators were not aware of the importance of this parameter. Before the accident it was
considered that the restrictions provided in the rules of operation, are connected with the necessity of
maintaining uniform energy deposition throughout the core. Although the developers of the reactor was
known (from analysis of data obtained at the Ignalina NPP) that for a small reactivity margin, protection
can lead to an increase in capacity, the appropriate changes were not made in the instructions. In
addition, no means for operational control of this parameter. Values that violate the regulations, have
been obtained from calculations made after the accident on the basis of parameters recorded by the
recording equipment. After the fall of the power the staff had deviated from the approved programme and
at its discretion, has decided not to raise the power up to 700 MW prescribed. According to A. S.
Dyatlov[12] this was done at the suggestion of a shift supervisor of block Akimova. Woodpeckers, as test
Director, agreed with the proposal, as in force at the time the regulation was no ban on working at this
level, and for tests of high power was not needed. IAEA experts believe that any deviation from a
predetermined test program, even within the rules, is unacceptable.

6. The consequences of the accident

During the explosion at the fourth reactor killed 1 person, another
died the same day from his injuries. The 134 employees of the
Chernobyl nuclear power plant and the emergency crews who
were at the station during the explosion, developed radiation
sickness, 28 of them died.[22]Shortly after the accident came the
divisions of fire brigades for the protection of nuclear power plants
and started extinguishing the fire, mostly on the roof of the turbine
hall.Two of the devices available on 1000 roentgens per hour for
one failed and the other was inaccessible due blockages.
Therefore, in the first hours of the accident no one really knew the
real levels of radiation in the premises of the unit and around it.
Unclear was the condition of the reactor.In the first hours after the
accident, many seem not aware of how badly damaged the
reactor, that is why I made the wrong decision to provide water to
the reactor core to cool it. These efforts were useless, as the
pipeline itself and the active area was destroyed, but they are
required to work in areas with high radiation. Other actions by the
station personnel, such as extinguishing the local fires station on
the premises, measures to prevent a possible hydrogen explosion,
etc., on the contrary, was necessary. They probably prevented
more serious consequences. When performing these works, many
of the station employees received large doses of radiation, and
some even fatal. Among them was the head of the shift Alexander
Akimov and operator L. Toptunov managing the reactor during the
accident.The release led to the death of the trees near the nuclear
power plant on an area of about 10 km2.

7. The accident

For liquidation of consequences of the accident were a government
Commission, the Chairman of which was appointed Deputy Chairman of the
Council of Ministers of the USSR Boris yevdokimovich Shcherbina. He
calculated the possibility of the application and developed the composition of
the mixture (boron-containing substances, lead and dolomite), which from the
very first day were thrown from helicopters into the reactor core to prevent
further heat-up the remains of the reactor and to reduce emissions of
radioactive aerosols in the atmosphere. Also it was he, riding on an armored
personnel carrier directly to the reactor determined that the readings of
neutrons on the ongoing atomic reactions unreliable, since they respond to a
powerful gamma-radiation. The analysis of the ratio of isotopes of iodine have
shown that in fact the reaction stopped[25].For coordination of works were also
created national Commission in the Belarusian, the Ukrainian SSR and the
RSFSR, and various departmental fee and staff. In the 30-kilometer zone
around Chernobyl began arriving experts, seconded to work in the emergency
unit and around it, as well as military units, both regular and urgent is
composed of reservists. All of them later became known as "liquidators". The
liquidators worked in the hazardous area in shifts: those who scored the
maximum permissible dose of radiation was gone, and in their place came
others. The bulk of the work was performed in 1986-1987, attended by
approximately 240 thousand people. The total number of liquidators (including
subsequent years) was about 600 thousandIn the early days the main efforts
were aimed at reducing radioactive releases from the destroyed reactor and
the prevention of more serious consequences. For example, there were
concerns that due to the residual heat in the fuel remaining in the reactor, the
melting of the active zone. The melt could penetrate the submerged space
below the reactor and cause another explosion with a large release of
radioactivity. The water from these areas was pumped out. Also, steps were
taken in order to prevent the penetration of the melt in the soil under the
reactor.According to the Russian state medico-dosimetric registry over the
years, among the Russian liquidators with doses of radiation above 100 mSv
(about 60 thousand), several dozen deaths could be associated with radiation.
Just 20 years in this group from all causes not related to radiation, died about
5 thousand liquidators.

8. Long-term consequences

The accident resulted from agricultural use was withdrawn about 5 million
hectares of land around the nuclear power plant created a 30-kilometer
exclusion zone, destroyed and buried (buried heavy machinery) hundreds of
small settlements.Map of radioactive contamination of the isotope cesium-137:
closed areas (more than 40 CI/km2) area of permanent control (15-40 CI/km2)
area of periodic controls (5-15 CI/km2) 1-15 CI/km2Before the accident in the
reactor of the fourth block was 180-190 tons of nuclear fuel (uranium dioxide).
According to estimates, which is currently considered the most reliable in the
environment were emitted from 5 to 30% of this amount. Some scholars
dispute these numbers, referring to the photos and eyewitness observations,
which show that the reactor is almost empty. However, it should be borne in
mind that the amount of 180 tons of uranium dioxide is only a small part of the
volume of the reactor. In addition to the fuel in the active zone at the time of the
accident were contained fission products and transuranic elements — various
radioactive isotopes that have accumulated during reactor operation. They
represent the greatest radiation hazard. Most of them remained inside the
reactor, but the most volatile substances were thrown out, including:all the
noble gases contained in the reactor; approximately 55 % of the iodine in the
form of a mixture of steam and solid particles, and an organic compound;
cesium and tellurium in the form of aerosols.The total activity of substances
released into the environment, was, according to various estimates, up to 14 ×
1018 Bq (14 EBK), including[29]1,8 EBK iodine-131, Of 0.085 EBK cesium137, 0,01 EBK strontium-90 and 0,003 EBK isotopes of plutonium; the share of
the noble gases contributed about half of the total activity.In 1988, the area
affected by pollution, was created radiation-ecological reserve[30].
Observations have shown that the number of mutations in plants and animals
although increased, but only slightly, and nature copes with their
consequences. On the other hand, the removal of the anthropogenic impacts
has a positive impact on the ecosystem of the reserve and the impact of this
factor significantly exceeded the negative effects of radiation. As a result, the
nature began to recover rapidly increased the population of animals increased
the variety of types of vegetation[

9. The impact of the accident on human health

Untimely, incomplete and contradictory official information about the disaster spawned a number of independent interpretations.
Sometimes the victims of the tragedy believe not only citizens, died immediately after the accident, but residents of surrounding
areas who came out to a rally without knowing about the accident.[33] in this count, the Chernobyl disaster greatly exceeds the
atomic bombing of Hiroshima by the number of victims.[34][35]
There is also the opposite point of view, referring to the 29 reported deaths from radiation sickness as a result of the accident (station
staff and firefighters, who took the first blow).[37] This view does not take into account the identified statistical studies of the growth of
mortality associated with elevated background radiation diseases in the contaminated areas.[source?] In addition, the mortality rate
among liquidators in Russia was lower than the national average, due to better medical care.[source?]The dispersion in the official
estimates less, although the number of victims of the Chernobyl accident can only be determined approximately. Except for the dead
plant workers and firefighters, they include cases of military personnel and civilians who were involved in liquidation of consequences
of the accident, and residents of areas affected by radioactive contamination. Determining which part of the disease was the result of
an accident is a serious challenge for medicine and statistics. It is considered[29] that most fatalities associated with radiation
exposure, have been or will be caused cancer.
The Chernobyl forum — an organization operating under the auspices of the UN, including such organizations as the IAEA and the
who in 2005 published a comprehensive report,[38] which analyzed numerous scientific studies of the influence of factors related to
the accident on the health of liquidators and the population. The conclusions contained in this report and in a less detailed review of
"Chernobyl's legacy", published by the same organization, differ significantly from the above estimates. The number of possible
victims to date, and in the coming decades is estimated at several thousand people. It is also noted that a slightly increased level of
morbidity among people who are not directly involved in the liquidation of the accident and relocated from the exclusion zone to other
places, not directly related to the irradiation (in these categories there was a slightly increased incidence of the cardiovascular
system, metabolic disorders, neurological diseases and other diseases not caused by exposure), but caused by stress associated
with the fact of resettlement, loss of assets, social problems, fear of radiation.
Given the large number of people living in the areas affected by radioactive pollution, even small differences in the assessment of
disease risk can lead to large differences in the expected number of cases. Greenpeace and a number of other public organisations
insist on the need to consider the impact of the accident on public health in other countries. Even lower doses of radiation make it
difficult to obtain statistically reliable results to make such estimates inaccurate.

10. The further fate of the station

After the accident at the 4th unit of the power plant operation was suspended
due to dangerous radiation environment. However, in October 1986, after
extensive work on decontamination of the territory and construction of the
"sarcophagus", the 1st and 2nd power units was again put into operation; in
December 1987, resumed 3rd.
In 1991, on 2-m unit, a fire broke out, and in October of the same year the
reactor was completely decommissioned. In December 1995, was signed the
Memorandum of understanding between the Government of Ukraine and
governments of the countries "the big seven" and the Commission of the
European Union, according to which began the development of a program of
complete closure of the station by the year 2000, 15 December 2000, was
permanently shut down the reactor last, the 3rd unit.
The sarcophagus built over the fourth exploded, the unit is gradually destroyed.
Danger in case of collapse, mostly is determined by how much radioactive
substance is inside it. According to official data, this figure reaches 95 % of the
number that was at the time of the accident. If this estimate is correct, then the
destruction of shelter can lead to very large emissions.
In March 2004 the European Bank for reconstruction and development
announced a tender for the design, construction and commissioning of a new
sarcophagus for Chernobyl. The winner of the tender in August 2007, he was
recognized as the company NOVARKA, a joint venture of French companies
Vinci in building greater success and BOUYGUES. [39]