Chernobyl disaster: What went wrong? Science

When an experiment went horribly wrong

A view of the closed reactor number 4 of Chernobyl nuclear power plant in Ukraine, with the Chernobyl Monument in foreground, erected in 2006.   | Photo Credit: Efrem Lukatsky

From discussing Louis Pasteur and his discovery of pasteurisation, we move on to document the Chernobyl disaster — considered one of the worst nuclear disasters to ever take place. April 26 marks the anniversary of this horrific accident, which released over 100 times more radiation than the atom bombs dropped at Hiroshima and Nagasaki during World War II.

Even though the disaster has come to signify the dangers of nuclear energy, it was in fact the result of a safety test that went completely wrong — partly due to design errors, and partly due to human flaws.

The experiment to be conducted by the engineers on duty at Chernobyl’s No. 4 reactor in the evening shift on April 25, 1986 was an attempt to see if the cooling pump system would continue to function using power from the reactor, even when the support systems for electricity supply fail.

What went wrong

Control rods, which perform the role of absorbing neutrons to slow down the chain reaction, are employed in nuclear reactors to regulate the fission process. Too many rods, however, meant that the system almost shut down, making it impossible for the test to take place.

Rods were raised to increase the power output and the automatic shutdown system was disabled so that the reactor could work under low power conditions. As the engineers continued to raise the rods, the power reached 12 per cent of normal output and the test began at 01:23 a.m. on April 26.

How it happened?

Within seconds, however, there was an enormous spike in the power levels that led to a steam explosion (water coolant turned into steam). Power reached roughly 100 times normal level and at 01:24 twin explosions occurred.

The reactor’s roof was blown off and radioactive particulate and gaseous debris was spewed out into the atmosphere. Air sucked into the shattered reactor resulted in a fire that burned for nine days.

Radiation levels were so high that it was practically impossible to attend to it for over a few seconds at a stretch. Engineers needed a containment solution for the exposed radioactive core that remained even when the fire was extinguished.

Eight months to contain radiation

Helicopters were used to drop thousands of tonnes of sand, lead and boric acid onto the reactor - to no avail. It was only in December that year that tonnes of concrete and lead were poured onto the reactor to control the radiation - efficacy and lifetime of which still remains a question.

Wildlife returns

A replacement shelter that will last for 100 years is planned to strengthen the existing mess. Scientists are however surprised by the fact that wildlife in the place has revived. Wild horse, boars and wolves are now seen in the area and birds are even found nesting in the reactor building.

As for the people, thousands were evacuated from the areas surrounding the reactor. Ukraine, Belarus and Russia were the worst affected, though traces of radioactive deposits from this accident were found in almost every country in the northern hemisphere.

While long term effects of the incident have been speculative, birth defects and instances of cancer have been blamed on this disaster. The number of people who could eventually die because of this experimental error continues to be a subject of debate.

Reach the writer at ganesh.a.s@thehindu.co.in


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Printable version | Sep 17, 2021 12:19:25 AM | https://www.thehindu.com/in-school/sh-science/when-an-experiment-went-horribly-wrong/article7143466.ece

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