How did the Chernobyl nuclear disaster happen?

Answer

Dear Thomas

On April 26, 1986, reactor unit 4 exploded in Chernobyl. This was the worst accident in the history of the peaceful applications of nuclear energy. In the meantime, both the causes and the consequences have been studied very thoroughly and many lessons have been learned.

The main causes of the accident were a number of human errors combined with the unsafe design of the reactor.

The unsafe and unstable design of the reactor: This type of reactor (RMBK, or in Russian ‘Reaktor Bolshoy Moshchnosty Kanalny’, which means ‘reactor
high power with ducts’), designed for the production of electricity, can also produce plutonium for military purposes. The problem with the RMBK type of reactor like in Chernobyl is that they behave unstable under certain conditions. Due to the various violations of operating procedures, the operators put the reactor in a dangerous state, resulting in a final explosion. RMBK power plants do not have an overarching building that completely isolates the reactor from the environment. This allowed the radioactive substances to spread much more easily in the environment.

For information; the nuclear reactors in our country that produce electricity are of a completely different type, namely pressurized water reactors (PWR or Pressurized Water Reactor in English).

The lack of theoretical training and knowledge of the operators, combined with a total lack of safety culture, led to the control rods (necessary to control the nuclear reactions in the reactor) being raised higher than allowed by the plant’s procedure. A second serious human error was the deactivation of the automatic protection just before the safety test that was carried out at the time. During that period (in the then cold war) safety was clearly not a priority.

An atmosphere of strict secrecy prevailed in the former Soviet Union: operators were not supposed to think critically or take initiatives in emergency situations that were officially unthinkable. Some urgent actions that should have been taken immediately in such a situation, such as extinguishing fires, stopping the nuclear chain reaction and informing the population, were delayed, causing this disaster to take on major proportions.

For more information, I would like to refer you to a publication by SCK•CEN, which describes the main technical elements and human errors that caused the accident, as well as the consequences for people and the environment. Meanwhile, UNSCEAR, a United Nations body, has published more up-to-date data on this.

Publication SCK•CEN “Chernobyl, 25 years later”: http://www.sckcen.be/-/media/Files/Public/Publications/Chernobyl_25y/Tsjernobyl_25jaar_later_NL_WEB.pdf

UNSCEAR publications (English only): http://www.unscear.org/unscear/en/chernobyl.html

Sincerely

Tom Claris
Scientific employee