Remembering the Chernobyl Nuclear Reactor Accident (26 April 1986)

An analysis is presented here about the Chernobyl nuclear reactor accident which occurred on 26 April 1986 discussing only the key points.

Remembering the Chernobyl Nuclear Reactor Accident (26 April 1986)It is extremely difficult to present a comprehensive and true picture of the Chernobyl disaster which occurred on April 26th, 1986 due to a number of peculiarities involved. Major problems were lack of transparency on certain matters in USSR at that time, deep media involvement, especially in the context of the cold war and genuine difficulties in the assessment of the long term implications of such an accident.

A correct and humanly move at the time of accident was organizing a precise scientific evaluation of the accident and its long term implications employing expertise and resources of the entire world in a non-political manner.

Unfortunately, it could not happen. View of the West about Chernobyl accident differed strongly from that of Soviet authorities. Soviets blamed Western media organizing a campaign to exploit the situation to defame the Soviet Union and its foreign policy. According to a critically analyzed report, ~100 petabecquerels of cesium-137 were released during and subsequent to the accident.

Major concern worldwide after the accident has been short and long term implications on human health in the affected regions of Northern Hemisphere. The Chernobyl accident has been under discussion till recently mainly in search of learning lessons about safety of nuclear technology.

Global safety is closely linked with the reliably safe function of nuclear technology worldwide. Accident at a nuclear reactor can be as severe as a nuclear attack. On 26 April 1986 at 01:23:45 a.m. reactor number four at the Chernobyl plant, near Pripyat in the Ukraine exploded.

Follow up thermal explosions threw out a plume of highly radioactive materials into the atmosphere, which then distributed over an extensive geographical area. The contaminated areas include extensive parts of the western Soviet Union, Europe and North America. Parts of the Lands of Ukraine, Belarus, and Russia were badly contaminated.

A photo of the destroyed nuclear reactor at Chernobyl is shown in picture below. RBMK (reactor bolshoy moshchnosty kanalny design – high-power channel reactor) design of the exploded nuclear reactor was to blame. RBMK reactor was a pressurised water reactor with individual fuel channels with ordinary water as the coolant and graphite as the moderator.

This design was basically for plutonium production. This reactor had a large positive void coefficient and was prone to high power surges when operated at low power levels. It was actually proved practically in Chernobyl accident.

Photo of the destroyed reactor made from the helicopter on May 3, 1986.

The presence of a water column under the displacer headed the reactor to the situation of positive reactivity produced by insertion of control rods. Major elements of the void reactivity problem in RBMK include great possible variation in the void reactivity and error in its determination as it is a difference of two observed values.

Void reactivity changes only slightly when burnup is less than 10 MWd/kg and starts increasing for higher values of burnup due to formation of plutonium in the early stage of burnup. It shows that a safety risk was involved in achieving high burnup. For higher burnup in RBMK design, less neutron absorbers were used in the core lattice. After the Chernobyl accident in 1986, additional neutron absorbers were installed in the RBMK cores to decrease the void reactivity coefficient.

Following the accident in reactor 4 of Chernobyl nuclear power station on 26 April 1986, a large amount of radioactive materials was released from reactor core into the atmosphere. The release of the radioactivity continued many days after the accident.

The release of radioactivity from the Chernobyl reactor 4 site decreased first and reached a minimum after which it started increasing due to thermal explosions produced by heat generated during radiation interactions with destroyed containment. Picture below shows the sarcophagus of Chernobyl nuclear reactor.

Chernobyl Nuclear Reactor

Lesson: In case of any nuclear accident, the accident place should be opened to the world for rescue efforts keeping the possibility of ill-will and enemy states in mind. There should be nuclear law making at the global scale regarding the reporting of nuclear news.

Dr Mukhtar Ahmed Rana

Mukhtar does research on Instrumentation, Physics, and Environmental Science.

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