The Chernobyl Disaster

The Chernobyl nuclear power plant disaster was the worst nuclear power plant accident in recorded history. The disaster occurred on April 26, 1986 in Pripyat, Ukraine. The isolation that occurred after the Cold War resulted in a lack in safety culture. This lack of safety culture led to employees lacking in training and improper management in regards to the power plant itself. People were unprepared to deal with a wrong doing on this scale.

Workers were preparing to start a test to determine how long turbines would spin and supply power to the main circulating pumps. The test was supposed to shed light on the loss of main electrical power supply. Workers had previously carried out similar tests; however, power from the turbine decreased significant, so new voltage regulator designs needed to be tested before use. The Chernobyl plant directed that the test needed to be postponed, which was a result of the lack of available power during the peak evening demand. However, operations not affecting power were still carried out. The workers disabled the emergency core cooling system intended to provide water to the core in case there was a loss of coolant. Once the test on reactor 4 started to begin, the operator went to shut down the reactor because of emergency.  

By this point, the reactor was already in an extremely unstable condition. A strange control rod design then led to a dramatic power surge as they were inserted into the reactor. Hot fuel reacted with cooling water and formed fuel fragmentation along with steam production and a large increase in pressure. The design of the reactor led to damage to multiple fuel assemblies, which ultimately resulted in the destruction of the reactor. Over pressure within the reactor ruptured the fuel channels and jammed all the control rods. Steam generation filled the core, which was caused from water dumped into the core when the cooling system was shut off. The steam caused an explosion and released fission products into the atmosphere. Very shortly after, another explosion occurred and sent fragments from the fuel channels and hot graphite.

Two workers immediately died from the explosion. Emergency crews responded to the accident and dropped boron, dolomite, sand, clay, and lead to extinguish the fire and limit the release of radioactive particles. Twenty-eight workers died within the first four months following the explosions, a result of severe radiation. The town of Pripyat was evacuated one day later. Approximately 100,000 square kilometers of land were significantly contaminated. The Soviet government evacuated about 115,000 people from the contaminated areas.

Shortly after the accident, 237 people suffered from acute radiation sickness, several hundred contracted thyroid cancer, and hundreds of thousands have contracted radiation poisoning. The disaster left radiation as a huge problem for many years following the explosion. The power plant was shut down, and it is now a popular tourist destination in Ukraine.

After the accident, the Nuclear Regulatory Commission emphasized the importance of several concepts. The NRC emphasized designing reactor systems properly on the drawing board and implementing them correctly during construction/maintenance, maintaining proper procedures and controls for normal operations and emergencies, having competent and motivated plant management and operating staff, and ensuring the availability of backup safety systems to deal with potential accidents. The emphasis on these aspects helps to ensure that disasters like this will not happen anywhere else. The estimated cost of direct loss following the disaster was fifteen billion.

  

    Sources: https://en.wikipedia.org/wiki/Chernobyl_disaster

http://www.nrc.gov/reading-rm/doc-collections/fact-sheets/chernobyl-bg.html

http://www.world-nuclear.org/info/Safety-and-Security/Safety-of-Plants/Chernobyl-Accident/