In 26 April 1986, a big accident occurred
at Unit 4 of the nuclear power station at Chernobyl, Ukraine, in the former
USSR. The power station was located 130 km north of the major city of Kiev and
the nearest town to the plant was city of Pripyat, which was home to around
50,000 people at that time. There was also a small town – Chernobyl – which was
home to around 12,000 people and the area was also surrounded by alot of farms
and forests. The four reactors at the Chernobyl power plant were built during
the 1970s and 1980s; and an artificial lake had been created, measuring 22
square km, in order to provide a water supply for the reactor. The plant used
four Soviet designed RBMK-1000 nuclear reactors, the design of which was later
found to be imperfect. These reactors used enriched uranium fuel to heat up
water to produce steam which then drives the turbines of the reactors and
creates electricity.
The day before the accident occurred, the
operating team were getting ready to test whether the turbines could produce
enough energy to run the coolant pumps if power was disconnected for any
reason, until the emergency diesel generator was switched on. In order to
prevent any interruptions to the reactor's power supply, the normal safety
systems were switched off purposely. Disabling the automatic shut-down system
was according to the U.N. Scientific Committee on the Effects of Atomic
Radiation (UNSCEAR) a big violation of safety regulations. To carry out the
test, the reactor had to be reduce its power to 25 percent of its normal
capacity. Unfortunately this did not go to plan and the power level of the
reactor fell hugely below 25 percent, to less than 1 percent. This meant the
power had to be slowly increased again, but 30 seconds after the test started
there was a sudden surge in power. The emergency shut-down systems which were
in place to stop a chain reaction, failed. The shocking result of this was
that, in the early morning of 26 April, the reactor's fuel elements ruptured
and a huge explosion occurred. The 1000 tonne sealing cap on the reactor
building was blown off and as temperatures reached over 2000°C, the fuel rods
melted. This caused the graphite covering of the reactor to ignite and it
burned for nine days, sending huge levels of radiation into the environment.
The explosion caused more radiation to be released than the nuclear bomb that
was dropped on Hiroshima in 1945.
There are two main view points on why the
disaster happened and both have been argued for a long time since the accident
occurred. Serious design mistakes in the power plant's cooling system almost definitely
caused the uncontrollable power surge that led to the Chernobyl tragedy. Most
Western nuclear reactors use water as a coolant, whereby as the core heats up
and produces more steam, the increase in steam bubbles in the water causes a
reduction in the reactivity of the nuclear core. This is a common and important
safety feature in most reactors – but not in the Chernobyl model which used
graphite as a moderator at the core; which caused a continuous loop of nuclear
reactivity and increase in the reactor's power output. This means the Chernobyl
design was unstable at low power levels and exposed to sudden flow in energy
production at dangerous levels. Moreover this element of the plant was not
known about by the crew.
The other view point is that the disaster
was caused by human error. Although serious mistakes had definitely been made,
almost all opinions nowadays are that the operator error was probably to lack
of training, experience and understanding of what they were doing. The plant
operators were surely wrong to disengage the safety and cooling systems, but
they had very poor experience and education in nuclear physics and engineering.
The Chernobyl disaster was the worst power
plant accident in history, generating higher costs and resulting in more deaths
than any other accidents. The operation following the event, to contain the
contamination and try to prevent further catastrophe, involved over 500,000
workers and cost over $200 billion dollars. The explosion killed two plant
workers immediately and in the following few days, 29 workers and fire fighters died in hospital
due to serious radiation sickness. The attempts to extinguish the burning
reactor were not successful, as fire fighters were extinguishing by water for 10
hours. Following this, 30 military helicopters flew over the site for 9 days
and dropped 2400 tonnes of lead and 1800 tonnes of sand trying to extinguish the
fire and absorb the radiation. but this made it worse
and it was only when the core was cooled
with nitrogen that the fire and emissions came under control.
The 600 men in the plant's fire service and
the operating teams were the most severely irradiated group, with 130 of these
being exposed to levels of radiation equivalent to 650 years’ worth of a
worker's safe annual limit. Thousands of military workers and others also helped
in the operations, moving radioactive material with little or no protective
clothing and equipment. Even though it is known for sure that 31 died in the
immediate aftermath the disaster, it is not known how many have died since then due
to the radiation they were exposed to; and of course how it has affected people
living in the area. One significant issue has been the large increase in
thyroid cancer in the years after the disaster, especially among children.
My point in the issue is that it seems
unfair that some of the authorities tried to put all blame on the workers
after the accident. The workers were the ones who suffered the most, either
through losing their life or suffering sickness after the radiation exposure. I feel they were taken
advantage of as they were working in a high risk environment and not provided
with all of the knowledge and training they needed.
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