Chernobyl is a small town in the Ukraine, near the border of Ukraine and Belarus, that was all until the Saturday, 26th April 1986 completely unknown city and after that became synonym for disaster, all because of the explosion inside the nuclear reactor which had caused the biggest nuclear disaster in history of the mankind. The nuclear power plant itself wasn't located in Chernobyl but in fact 18 km northwest of the city of Chernobyl, near the town of Pripyat and was consisted of four reactors of type RBMK-1000, of which reactor Number one was commissioned in 1977 and fatal reactor Number four in 1983. (Click Here)
Chernobyl power station with these four reactors combined produced about 10% of total Ukraine's electricity. The explosion itself was major issue in all the world media and the great fear in safety of soviet nuclear stations arise. Even the Soviet government, under pressure of the world media had to reveal the mystery veil from their nuclear projects since further explosion, all caused by the primary explosion inside the nuclear reactor, had spread radioactive cloud outside the Soviet border and into the east, west and north Europe and even in the some parts of the North America.
An aerial view of the Chernobyl nuclear power plant (May 1986 photo) after the April 26 explosion in Chernobyl, Ukraine. In front of the chimney is the destroyed 4th reactor. Behind the chimney and very close to the 4th reactor is the 3rd reactor.(Click to Enlarge)
The facility had been built during the 1970s using a design that lacked some of the safety features in many other nuclear power plants. Most notably, Chernobyl's reactors were not enclosed in sturdy containment buildings, like the massive concrete domes seen at other nuclear plants. Such shells are able to trap any radiation that accidentally escapes from the reactor core, the site of the nuclear fuel. In the former Soviet Union at least 9 million people have been affected by the accident; 2.5 million in Belarus; 3.5 million in Ukraine; and 3 million in Russia. In total over 160 000 Km2 are contaminated in the three republics.
As far away as the United Kingdom, restrictions are still placed on the movement and slaughter of sheep. In January 1996 these restrictions were still in place in 219 farms effecting 317,400 sheep and covering more than 1097 km2. The accident at Chernobyl was due to multiple operating mistakes that compounded the serious design flaws. Therefore, the safety culture actually is very important to prevent unwanted accident to be happening.
Repairs are carried out on the Chernobyl nuclear plant in Ukraine on October 1st, 1986, following a major explosion in April 1986 which, according to official statistics, affected 3,235,984 Ukrainians and sent radioactive clouds all over Europe.
The Number 4 reactor of the Chernobyl nuclear power plant in the Soviet Ukraine suffered a power excursion on April 26, 1986. The accident happened during the effects test of running the reactor at low power. To perform the test, one of the important control systems was switched off and in order to allow the reactor to reach unstable and low power condition. An unplanned decision from a deputy chief engineer who gave an order to lift the control rods to speed up the reaction proved to be the biggest mistake.
This mistake has caused the water reactor drained and began to overheat. The tremors are felt and in panic situation, all the control rods were lowered and suddenly it jammed. This event has lead to another problem. The power in the reactor was increased abruptly about 100 times from its nominal value. The light water coolant, no longer able to carry off the enormous amount of heat generated, evaporated in a fraction of seconds, leading to a steam explosion.
The reactor was destroyed. In the following ten days or so, about 300 Mega Curies of radioactive isotopes injected into the atmosphere, significantly contaminating an area of about 150 000 square inhabited by some 6 million people. It also caused a measurable increase in the level of ionizing radiation in most of Europe.Unfortunately, the accident happened because of the violation of the safety regulation by the operator. Other cause such as the unsafe reactor design has also contributed to this accident.
A military helicopter sprays a decontaminating substance over the region surrounding the Chernobyl nuclear power station a few days after its No. 4 reactor's blast.
A graveyard for vehicles highly contaminated by radiation, near the Chernobyl nuclear power plant, seen on Nov. 10, 2000.
A view of the Chernobyl nuclear power station is seen from Ukraine's ghost town of Pripyat, April 13, 2006.
This condition turned from bad to worst with the potential of reactor’s breakdown and explosion occurred. The event was related with the design of nuclear reactor. The Reaktor Bolshoy Moshchnosti Kanalniy (RBMK) was built with a class of graphite-moderated and cooled by light water. The moderator blocks are made of nuclear graphite of dimensions 250×250×500 mm.(Click Here) The control rod design was identified as unsafe.
Discussing about the control rods design, the RBMK at Chernobyl had manual control rods. Some RBMK designs did include control rods on electromagnetic grapples, thus controlling the reaction speed and, if necessary, stopping the reaction completely. Thus with the design it can reduce the fission rate before it gets too high. The reactor also has an unsafe void coefficient. For the test, the reactor should have been stabilized at about 1 000 MWt prior to shut down, but due to operational error the power fell to about 30 MWt.
When the operational error happened, the void coefficient of reactivity was so positive that it overwhelmed the other components of the power coefficient, and the power coefficient itself became positive. When the power began to increase, more steam was produced, which in turn lead to an increase in power. The additional heat resulting from the increase in power raised the temperature in the cooling circuit and more steam was produced.
More steam means less cooling and less neutron absorption, resulting in a rapid increase in power to around 100 times the reactor's rated capacity. There was an increase in coolant flow and a resulting drop in steam pressure. At about this time, the operators reduced the flow of feed water, presumably to maintain the steam pressure. The automatic trip which would have shut down the reactor when the steam pressure was low had been circumvented.
Another unplanned decision was made by the operator in charge. In order to maintain power the operators had by switching off the automatic regulators and freeing all the control rods manually. The reactor became very unstable where the operators could not prevent an overwhelming power surge and had to make adjustments every few seconds trying to maintain constant power.
A close view of reactor number 4 of Chernobyl nuclear power plant in this May 10, 2007 picture, with the Chernobyl Monument, left, erected in 2006.
In this Nov. 10, 2000 photo, the control room with its damaged machinery, is seen inside reactor No. 4 in the Chernobyl nuclear power plant.
An employee of the Chernobyl Nuclear Power Plant walks in the control room of the destroyed 4th block of the plant on February 24, 2011.
A raven stretches its wings as it sits on a post inside the 30 km (18 miles) exclusion zone around the Chernobyl nuclear reactor near the village of Babchin, Belarus on December 23, 2009. The sign reads: "Radiation hazard".
Explosion was the next event happed after the failure of reactor design. The control rods are made of boron carbide with a graphite tip. When the control rod is first inserted, the graphite tip increases the reactivity. Graphite also consists in the reactor’s neutron moderator about 600 tones. Unfortunate property of that material leads to a huge explosion. This is happened due to very hot graphite comes into contact with air then it bursts into flames and the fire burned for 10 days.
At Chernobyl the graphite fire vaporized the radioisotopes in the reactor and dispersed them in the atmosphere together with the smoke. The accident caused the deaths of thirty one persons due to the acute effects of the explosion. The explosion killed two members of the operating crew. Additional for the accident it has created fear to human nation due to radiation effect.
There were 134 persons who were acutely irradiated and from that number 28 died in the three months following the accident. In response, the authorities evacuated, in 1986, about 115,000 people from areas surrounding the reactor and subsequently relocated, after 1986, about 220,000 people from Belarus, the Russian Federation and Ukraine.
In conclusion, the Chernobyl accident resulted from a combination of external circumstances, engineering design flaws and errors made by badly trained operators. The test was started at extreme operating conditions. Closing the valve to the turbines increased boiling of the coolant. The positive void coefficient started a power excursion which accelerated when the poisoning of the core decreased as the flux increased.
This could have been stopped by the control rods, had they not been too far out of the core, as well as badly designed. Instead, the control rods delivered the final blow. The fuel rods went white-hot and shattered. The hot fuel made the water dissociate into hydrogen and oxygen. The cooling system exploded from the pressure of the steam, then the hydrogen could react with the air outside and there was a chemical explosion.
The Chernobyl accident had a disastrous impact on life, health and the environment especially in Ukraine, Belarus and Russia and prompted fear and concerns in other nations of the world about the effects of radiation. In addition, it has had a negative impact on the health of the hundreds of thousands of people involved in the clean-up and those who still live in heavily contaminated areas. Therefore, safety culture needs to be improvising for the future planning of the development nuclear power plant. This is to ensure that there is no other future accident happened again.
General view of Ukraine's ghost town of Pripyat, April 13, 2006.
An abandoned house seen in the deserted village Redkovka, some 35 km (22 miles) from Ukraine's Chernobyl nuclear power plant, Thursday, March 30, 2006.
A Ukrainian man with a dog walks in a street in the ghost town of Chernobyl, April 13, 2006.
"It is unlikely that we can meet our aggressive climate goals if we eliminate nuclear power from the table. However, there is no future for expanded nuclear without first addressing four key issues: public right-to-know, security of nuclear fuel and waste, waste storage, and proliferation." - Barack Obama,
Regards,
~Nuclear Boy~
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