On April 26th, 1986, the world was shook by an explosion. The worst case peace-time scenario had occured…thermonuclear meltdown. Some 110 km from the capitol of Ukraine, a nuclear power station spewed tons of deadly radioactive material across the globe. A city was laid desolate, thousands were contaminated. Even today, the long reaching effects still haunt us.

As with many accidents, this one was preventable. The three main causes: a poorly designed reactor, incompentance at the administration level leading to and during the accident, and a goverment system designed to hide, not fix problems.

Still under the yoke of Soviet Communism, the scientific community lived with the mentality of “Hear no evil, see no evil, speak no evil.” Under no circumstances did one want to rock the boat. Although there were inherent problems spread all over their nuclear power program, things were not discussed, accidents were covered up, information was not shared. Although the reactor had a design flaw, who was going to talk about it. In his book Chernobyl: Insights From the Inside, V. Chernousenko states, “It was the secrecy and lack of accountability of our nuclear science, and its refusal to open itself up to discussion and criticism which made possible for dangerous design faults to lead finally to a nuclear explosion of this scale.”

Chernobyl power station was a 4 reactor nuclear power facility (with 2 more being added). The Soviet designed and built RBMK reactor was the most powerfull reactor in the world, producing from 700 to 1250 megawatts of energy.

In a nuclear reactor, uranium 235 is used to produce energy. As neutrons bounce around, they split uranium 235 nuclei releasing power as heat. The heat is captured in water producing steam which in turn cranks turbines which create electricity. The RBMK design was a one used in early nuclear reactors. It used 4 seperate components to control the reaction. Uranium is the only material known to support a nuclear chain reaction. Graphite was used in order to slow down the neutrons allowing them to collide with the uranium atoms (called the moderator). Water was used as a coolant and to produce steam. Boron was used as a neutron absorber to slow or shut down the fission reaction. So water is present in the chamber with the uranium and graphite. Neutrons bounce around and hit uranium nuclei, splitting them and releasing energy as heat. More neutrons are also released hitting more uranium atoms and releasing more neutrons, ad nauseum. The heat acts upon the water creating steam. Once the steam is used to power the turbines, its captured, cooled and the water is reused. The boron can be raised or lowered around sections of the fuel thus stopping the reaction.

The problem with the RBMK reactor is called Positive Void Coefficient. This basically means “Someone really screwed up this design”. When too much steam was present in the core, things would get ugly. Too much steam meant not enough water cooling the reactor. Because the graphite rods would still be in place, the temperture would rise, this would cause more steam to be produced, thus causing the temperature to rise more…until the thing exploded. Newer reactor designs avoid this problem by using water as both a coolant and moderator. An excess of steam would cool the reactor, not heat it.

On the day in question, Reactor No.4 was scheduled to power down for some maintenance. While powering down, a test was scheduled to see how well the turbines would run once main power was shut off until the backups fired up. One of the main safety features was specifically wired to not work. It bypassed many of the checks and balances in the system. At the same time, some safety features, such as an emergency water system were locked down so that they would not interfere with the test.

The man in charge, Dyatlov, having experience as an electrical engineer was unfortunately not a nuclear station technician. He had lots of theory, but no practical experience. Grigory Medvedev, a nuclear physicist and engineer who was subsequently sent by Moscow to research what happened, had warned the station director years previously of Dyatlov’s unsuitability and incompetence as an administrator. He is described as having no sense of danger or caution and frequently disregarded the safety of the station and technicians. Much of the damage and death that ensued can be attributed to him.

To be continued…

For more reading, see:
Wikipedia article
MSN Encarta article
Nova Online timeline
Acute Radiation Syndrome: A Fact Sheet for Physicians
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