The 1986 Chernobyl disaster took place at a nuclear power plant in the Ukrainian SSR. One of the four reactors in the plant exploded due to unstable conditions and a lack of safety procedures. The disaster left areas surrounding the reactor exposed to harmful radioactive materials, which also traveled to other areas, including present-day Belarus and the Russian Federation. Studies conducted on the radiation in the area have revealed that the disaster led to a number of health and environmental issues, along with the deaths that occurred shortly after the event.
What Caused the Chernobyl Disaster?
The Chernobyl Nuclear Power Plant was constructed in the late 1970s and early ‘80s. It consisted of four RBMK reactors, which could generate up to 1,000 megawatts of electric power per reactor. RBMK is a Soviet-designed boiling light water reactor that uses uranium dioxide fuel. The plant was stationed in present-day northern Ukraine, about 130 kilometers north of Kyiv and about 20 kilometers south of the Belarus border. RBMK reactor Units 1 and 2 were constructed in the 1970s, and Units 3 and 4 were completed by 1983. Plans for additional reactors were in place when the disaster occurred.
On April 25, 1986, a test was conducted during a routine maintenance shutdown to see if the reactor could produce electrical power for emergency equipment in the event that the station lost power. However, the test was performed when the reactor was in an unstable condition. The power was reduced significantly below the level it should have been to stabilize the reactor’s condition prior to shutdown. The RBMK reactor has a positive void coefficient, which means that steam production increases when power is increased, or water flow is decreased. This process causes fuel temperatures also to increase. When power levels are very low, it causes the positive void coefficient to become dominant. As a result, it creates unstable conditions for the reactor and makes it vulnerable to sporadic power surges.
Plant operators attempted to increase the power level to a stabilized condition. Control rods are used to help keep the reactor controlled. However, only a handful of rods were used during the test compared to the minimum 30 rods required for safe operations. In an effort to maintain constant power, operators removed most of the control rods. This compromised the condition of the reactor even further. As operators continued to try and maintain power and steam pressure, they decided to lessen the amount of water needed to cool the reactor. A steam explosion occurred due to increased heat and steam production, and a second explosion followed seconds later.
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The first explosion destroyed the reactor core and caused the cover of the reactor to be lifted. It also caused more than 1,500 pressure tubes to rupture. The reactor core was exposed following the second steam explosion, which is largely responsible for the release of radioactive materials into the environment. The explosions occurred at around 1:23 a.m. on April 26, 1986. Assessments of the accident determined that the cause of the explosions was due to a lack of safety procedure practices on part of the plant operators and some flaws in the design of the reactor.
Immediate Aftermath of the Accident
Fragments and hot graphite were thrown out from fuel channels and the reactor. A number of fires started, which contributed to more radioactive materials being released into the atmosphere. Throughout the day of April 26, hundreds of tonnes of water were injected into one-half of the reactor that was still partially intact. Injecting water into the reactor was halted after concerns grew over water possibly leaking into the Unit 1 and 2 reactors. Thousands of tonnes of sand, clay, boron, and other materials were dumped onto the reactor core to extinguish the fire at the core and prevent the release of any more radioactive particles. This process took place for about nine days.
One operator died when the explosions occurred, and another died in the hospital hours later as a result of injuries. Within 36 hours of the accident, about 49,000 residents in the nearby town of Pripyat were evacuated from the area. Within three weeks of the accident, about 116,000 people living within a 30-kilometer radius of the Chernobyl plant were relocated to less contaminated areas. In 1986 and 1987, about 240,000 emergency workers were called in to help clean up the site. Within the first few weeks of clean-up, 28 individuals died as a result of Acute Radiation Syndrome (ARS) due to high amounts of radiation exposure.
Radioactive Materials Released into the Environment
The Unit 4 reactor explosion released more than 100 radioactive elements into the environment. Some elements had shorter lives, while others were still present within the Chernobyl Exclusion Zone (CEZ). The CEZ is known as the area within 30 kilometers of the plant. Some of the most dangerous radioactive elements released into the atmosphere after the explosion included iodine, caesium, and strontium. Most radiation exposure that occurred shortly after the accident was caused by Iodine-131. This radioactive element has a half-life of eight days. Caesium-137 was more hazardous long-term, with a half-life of about 30 years.
Scientists conducted a study on the crops in the Chernobyl region to test their level of radioactive contamination 25 years after the accident occurred. Almost half of the samples they collected still contained Strontium-90, considered very dangerous for human consumption. A small population of inhabitants who were previously evacuated from the site at the time of the accident has since returned. The CEZ is illegal to live in; however, some inhabitants have decided to resettle in the area.
Throughout the years since the accident, scientists and researchers have studied how different concentrations of radiation in materials surrounding the site have affected the health of inhabitants. These studies also provide insight into how long-term exposure to certain radioactive elements affects human health. Dust and debris dispersed most of the radioactive elements into surrounding areas. The soils in the CEZ also contained radioactive elements.
Wind and weather conditions caused some of these materials to travel to other regions. Radioactive fallout occurred in many parts of the northern hemisphere. Large parts of Ukraine, Belarus, and Russia experienced heightened levels of radioactivity. Some parts of Scandinavia and Europe also experienced minor contamination. The amount of contamination in these areas varied due to the inconsistent distribution of radioactive elements caused by natural weather conditions. About 190 metric tons of fission products and uranium dioxide fuel were in the Unit 4 reactor. Soviet scientists estimate that up to 30% of these products were released into the environment.
Effects of Chernobyl Radioactive Elements on Humans & Wildlife
People who were most impacted by exposure to radioactive elements were the emergency responders who spent time cleaning up the Chernobyl disaster site. Many suffered from ARS, which causes burns, headaches, fevers, and gastrointestinal issues. High amounts of exposure to radiation were more dangerous to these individuals compared to those who have been exposed to lower levels long-term.
A study conducted by researchers at the National Institutes of Health (NIH) concluded that children exposed to radioactive iodine had an increased risk of being diagnosed with thyroid cancer. Iodine from the accident gave off radiation that disrupts the chemical bonds in a human’s DNA. Tumors were also found in individuals exposed to high radiation doses.
Scientists and researchers used the Chernobyl disaster as an opportunity to conduct studies on how animals were affected by radioactive fallout. One study showed that eastern tree frogs in the CEZ went through a quick evolutionary change. The frogs located near the Chernobyl site were pitch black in color compared to other individuals of the same species in other places. This evolutionary process took place over ten generations of the eastern tree frogs living in the CEZ.
Genetic changes and mutations also affected other animals in the CEZ. Birds that were exposed to high levels of radiation had visible tumors. Some birds and mammals also exhibited partial albinism. Researchers determined that the Chernobyl disaster would have long-term effects on the biological systems of species and ecosystems present in the CEZ.
Responses to the Chernobyl Disaster
The Chernobyl disaster devastated the area surrounding the plant and directly affected the nearby inhabitants of Pripyat. Thousands of people were directly exposed to harmful radioactive materials released from the reactor core upon its explosions. Fires that broke out from the accident caused radioactive elements to be distributed into the atmosphere. Present-day Ukraine, Belarus, and the Russian Federation were most affected by radioactive contamination. Approximately 6.4 million people were living in areas that were contaminated.
Radioactive materials are still present in Chernobyl, but exposure levels are much more tolerable. However, long-term exposure continues to pose a threat to human health. Several safety measures were taken in response to the Chernobyl accident to prevent future accidents from occurring. The International Atomic Energy Agency (IAEA) stepped in to assist countries in the former Soviet Union and Central and Eastern Europe in identifying issues in the RBMK reactor design. Design improvements and upgrades were made to the RBMK reactors to eliminate any deficiencies. The IAEA also assisted in increasing operational safety awareness.
The Unit 4 reactor was covered with a temporary concrete and steel shield, known as the “sarcophagus,” to prevent more radioactive elements from being released into the environment. The sarcophagus was built in May 1986 and encloses the entire Unit 4 reactor. Concerns over the condition of the sarcophagus and its deterioration due to radiation led to the launch of a new project to shelter the reactor. The New Safe Confinement was built off-site and placed over the sarcophagus in 2016. The structure is made of steel and is expected to last for at least 100 years.
The Chernobyl disaster was an eye-opening disaster that led to increased safety efforts. The effects of the accident led the Ukrainian government to push sustainable energy measures to reduce the need for nuclear energy. A solar power plant with 3,800 solar panels sits across from the Chernobyl disaster site, which provides power to thousands of apartments. All reactors were shut down over time, with the last reactor closed in December 1999. Decommissioning of the site officially began the following year, which included the removal of wastes and decontamination of the area. Due to the presence of radioactive elements, clean-up of the CEZ is expected to take several decades.