A Colloquium presentation on the Chernobyl Nuclear Power Plant disaster of 1986.

1. Angshuman Pal
B. Mechanical E. – IV (A-2-2)
001411201048
Jadavpur University
THE CHERNOBYL DISASTER

2. Contents
 Introduction to Nuclear Power
 Nuclear Reactors
 Nuclear Energy
 Power Generation
 History of Nuclear Reactors
 Nuclear Safety
 The Chernobyl Disaster of 1986
 Events and Occurrence
 Causes
 Operators Error
 Design Deficiencies
 Response
 Conclusion
 References

3. Introduction
 The human civilization and all other life forms on
Earth sustain themselves from the energy we
receive from the sun.
 Energy, the most vital ingredient for maintaining
life, in most forms, is chiefly obtained from
incoming radiation from the sun.
 The concept changed radically and forever, with
the discovery of nuclear energy by Prof Albert
Einstein at the dawn of the 20th century.
 Within the next hundred years, course of
progress of the civilization would be altered
permanently as a result of the pool of nuclear
energy becoming available to humans.

4. Nuclear Energy
 Nuclear energy is derived from the phenomenon of
nuclear reactions.
 The study of Chemistry since ancient times denoted
atoms of an element as the most fundamental
constituent of matter which takes part in reactions
 Chemical reactions, i.e. interactions between
elements or combinations of elements, was known to
be a phenomenon caused by sharing and transfer of
electrons
 This concept of elemental reactions changed as the
phenomenon of nuclear reactions was discovered as
a result of the discovery of the possibility of harvesting
nuclear energy.

5. Nuclear Energy (contd.)
 Nuclear reactions are distinguished into two
categories: fission and fusion. Both involve
changes occurring within the constitution of the
nucleus of the atom.
 A nuclear reaction is capable of generating
energy which is of a magnitude enormously
greater than that possible by a nuclear reaction.
According to Einstein’s mass energy equivalence,
where E is the amount of energy produced when
m unit of mass is converted into energy through
nuclear reactions, c being the speed of light. The
speed of light is , so 1gm of a radioactive material
is potentially capable of providing 90000 GW of
energy, which is cannot be possibly imagined in
case of conventional chemical reactions.

6. Power Generation
 Conventional thermal power reactors work on the
principle of the Rankine cycle where water is heated
to form steam at high pressure.
 The steam is passed through a steam turbine,
transferring the thermal energy carried by the steam
to kinetic energy of the turbine runners.
 A nuclear power plant operates in a manner similar to
a thermal power plant, except that the heat generated
to create the steam comes from nuclear reactions and
not from burning coal.
 The raw radioactive material like uranium is extracted
from its ore, and is usually converted into a stable and
compact form (yellowcake) before transportation. The
yellowcake is converted to Uranium hexafluoride
(UF6), enriched, given a particular shape and
geometry, and finally sent to the reactor.

7. History of Nuclear Reactors
 After the disastrous effects of the atomic bombings in
Japan in 1945, worldwide efforts were concentrated
on channelizing the efforts and benefits of nuclear
science towards socially beneficial causes.
 The Obninsk power plant in USSR was the first
nuclear power generator to produce electricity for the
grid, producing 5 MW power. The United States was
the leader in investigating in nuclear powered marine
devices like submarines and aircraft carriers.
 At present, according to data maintained by the World
Nuclear Association, there are over 440 commercial
nuclear power reactors operational in 31 countries,
with over 390,000 MW of total capacity. 55 countries
operate a total of about 250 research reactors, and a

8. Nuclear Safety
 Breach of nuclear safety mainly implies exposure to
radioactive radiation and uncontrolled emission of
nuclear energy.
 Exposure to nuclear radiation at high intensity can
cause immediate death. At lower intensity, radiation
can cause permanent deformation of body parts and
cause life-threatening cancer.
 The ill effects of radiation are harmful enough to not
only destroy a single generation but also percolate
down to members of upcoming generations, who may
be born with abnormal body parts and functioning.
 The vicinity of the region where a breach of nuclear
safety has occurred may become incapable of
sustaining life for a long time after the event.

9. Nuclear Safety: Radiation Protection
System (RPS)
 Reactor Protection System (RPS) is the standard medium
is designed to immediately terminate the nuclear reaction.
It has two components: Control rods and Standby Liquid
Control.
 Control rods are a series of rods that are inserted into
the core of the reactor to immediately halt the nuclear
reaction. They absorb the neutrons in the reactor. The
rods are typically made of lanthanides, actinides,
transitions metals or alloys. The material has to be
neutron-absorbing, have a low thermal expansion
coefficient, and have self-lubricating properties.
 In case of failure of the primary cooling system of the
reactor, standby liquid control is made operational. The
coolant circuit loss can either be compensated by
flooding with ordinary water or through a solution

10. Nuclear Safety: Emergency Service
Water System (ESWS)
 The Emergency Service Water System (ESWS) is
responsible for dissipating the spent heat and
decay heat back into the environment.
 Water in huge quantities is drawn from nearby
water bodies and passed through the reactor’s
heat exchangers. Impurities is water can cause
clogging of the reactor parts as well.
 The water carrying the spent heat is then
released back to the environment. This is
effectively a mean of environmental pollution and
hazard to marine environment as well.

11. Nuclear Safety: Emergency Core
Cooling System (ECCS)
 Emergency Core Cooling System (ECCS) is designed
to safely shut down a nuclear reactor during accident
conditions.
 The ECCS allows the plant to respond to a variety of
accident conditions and additionally introduce
redundancy so that the plant can be shut down even
with one or more subsystem failures.
 This system follows methods like introducing coolants
at high pressure into the reactor, spraying of coolant
near the region of failure to contain the failure and
ensure safety to nearby regions, depressurizing the
steam, etc.

12. The Chernobyl Disaster of 1986
 The Chernobyl Nuclear Power Station, located in
northern Ukraine of erstwhile USSR, was a 4000
MW capacity station which produced 10% of
entire Ukraine’s power needs.
 The plant consisted of four RBMK type reactors,
the first of which was constructed in 1977 and the
fourth in 1983.
 Two more reactors had been scheduled for
construction, prior to the disaster which occurred
in 1986.
 Following the disastrous events of 1986, the
reactor was slowly decommissioned and the
plans for construction of two more reactors was

13. Events and Occurrence
 On 26th April 1986 in the early hours of the morning, the
fourth reactor suffered a calamitous collapse. During a
late-night safety test which simulated a station blackout
power failure with the safety systems deliberately turned
off, a combination of reactor design flaws and overlooking
of certain safety conditions by the operators in arranging
the core, uncontrolled reaction was initiated.
 Steam explosion and open-air graphite fire resulted, with
the draught from the fire lasting 9 days. Radioactive
emissions into the atmosphere occurred which would
eventually precipitate all over the landmass of Eastern
Europe.
 The immediate blast caused two deaths at the facility with
134 hospitalized, of whom 28 firemen and employees died
within a short span of time post the incident. 14 other
cancer deaths were reported in the next 10 years. The
complete determination of the extent of damage caused is
expected to become clear within a few decades. Complete
cleanup of the site is expected by 2065.

14. Causes: Operator Error
 There is alleged to have been gross overlooking and
negligence on part of the operators responsible for
safety of the power plant and conducting of the safety
tests on the night of the event.
 There are said to have been gross violations of the
operating rules coupled with lack of experience and
training of personnel in the physics and engineering of
nuclear reactors. The technical procedures were said
to be insufficiently clear to the workers.
 More specifically, when the primary purpose of the
safety procedure was to test the performance of the
generators in case of a nuclear emergency, the
generators themselves were switched off thus making
the entire procedure useless.
 Valery Legasov, Soviet scientist, had commented on
the matter: “It was like airplane pilots experimenting
with the engines in flight".

15. Causes: Design Deficiencies
 It was only after the initial report was submitted blaming
operator’s error for the disaster, various design
deficiencies and incorrect management of operator
instructions emerged, which compounded the scale of the
disaster.
 There had been previous reports of structural damages
reported during the construction of the plant, but according
to KGB documents relevant to the period such allegations
were never acted upon.
 Later reports alleged that most of the information provided
in the report of the International Nuclear Safety Advisory
Group (INSAG) in August 1986 to be erroneous or highly
irrelevant. Turning off the Emergency Core Cooling System
interfering with the protection equipment settings, and
blocking the level and pressure of the separator drum were
not fundamental causes behind the explosion although
they might have been breach of regulations.

16. Causes: Design Deficiencies (contd.)
 Some of the identified errors and deficiencies in design are as
follows:
 The void coefficient in a nuclear reactor is a number that can
be used to estimate how much the reactivity of a nuclear
reactor changes as voids form in the reactor coolant. For the
Chernobyl reactors the coefficient was significantly positive
where as it is generally expected to be negative. Thus
neutrons were slowed down even if steam bubbles were
present in the water, thus precipitating faster reaction.
 Steam absorbs much less readily than water. Increasing the
intensity of vaporization implies that more neutrons are able to
split uranium atoms, increasing the reactor's power output.
This makes the RBMK design very unstable at low levels of
power.
 The design of the control rods as a part of the RPS was faulty,
and of considerably shorter length.
 Other deficiencies besides these were noted in the RBMK-

17. Response
 The problems related to the 1986 disaster
continued to haunt the Soviet authorities for a
long time, ultimately leading to decommissioning
of a number of reactors following further
accidents at the site.
 The future plans for construction of a fifth and
sixth reactor at Chernobyl were put on hold and
ultimately scrapped.

18. Response: The Sarcophagus
 The Chernobyl reactor is now enclosed in a large
concrete sarcophagus. The damaged reactor was
sealed off and 200 cubic meters of concrete was
placed between the disaster site and the
operational buildings, which was built quickly to
allow continuing operation of the other reactors at
the plant.
 A New Safe Confinement was to have been built
by the end of 2005; however, it has suffered
ongoing delays and as of 2010, when
construction finally began, was expected to be
completed in 2013.
 The fourth reactor still remains out of bounds for
people and workers. A handful of Ukrainian

19. Response: Radioactive Waste
Management
 Even today, some radioactive fuel remains in the
reactors at units 1 through 3, most of it in the
spent fuel pool, as well as some material in the
interim storage facility pond.
 Contracts were given for clearing of radioactive
waste by the Ukrainian government to clear up
the fuel in canisters. The canisters were to be
transported to dry storage vaults, where the fuel
containers would be enclosed for up to 100 years.
 In January 2008, the Ukrainian government
announced a 4-stage decommissioning plan that
incorporates the above waste activities and
progresses towards a cleared site.

20. Response: Alienation Zone
 An area originally extending 30 in all directions from
the plant is officially called the "zone of alienation".
 It is largely uninhabited, except for about 300
residents who have refused to leave. The area has
largely reverted to forest, and has been overrun by
wildlife because of a lack of competition with humans
for space and resources.
 Even today, radiation levels are so high that the
workers responsible for rebuilding the sarcophagus
are only allowed to work five hours a day for one
month before taking 15 days of rest.
 Ukrainian officials estimated the area would not be
safe for human life again for another 20,000 year.

21. Conclusion
 The Chernobyl disaster of 1986 proved to be a wake-up
call for the generation of worshippers of nuclear energy
about the disastrous consequences of irresponsible
construction and management of nuclear reactors.
 On one hand, nuclear energy provides an unparalleled
solution to the world’s energy problems, the degree of
precaution required and the consequences of a breach of
safety are of a magnitude enormously higher than an
ordinary thermal power plant.
 Post Chernobyl, the biggest nuclear reactor disaster has
been the Fukushima Daiichi power plant disaster in 2011
as a consequence of the devastating earthquakes and
tsunamis in the Pacific Ocean which left Japan devastated.

22. Conclusion (contd.)
 Overall, awareness to the dangers of nuclear
radiation is definitely increasing.
 Governments all over the world paying
considerable attention to achieving a permanent
solution to not only the situation caused by
nuclear weapons, which merits the most
attention, but also to a sustainable future where
nuclear power is used for purposes beneficial to
mankind.
 This future requires an inclusive effort from the
society, governments and common people in
general, where the right mix of precaution and
progress are adopted in order to achieve a future
which is safe sound and secure for all.

23. References
 World Nuclear Association (http://www.world-
nuclear.org/)
 The Chernobyl Nuclear Power Plant
(http://chnpp.gov.ua/en)
 Wikipedia
 https://en.wikipedia.org/wiki/Chernobyl_Nuclear_Po
wer_Plant
 https://en.wikipedia.org/wiki/Chernobyl_disaster
 https://en.wikipedia.org/wiki/Nuclear_power
 https://en.wikipedia.org/wiki/Nuclear_reactor_safety
_system