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The mysterious Chernobyl explosion: Why did the reactor go out of control?
On April 26, 1986, a huge explosion occurred in the No. 4 reactor of the Chernobyl Nuclear Power Plant, becoming one of the worst nuclear disasters in history. The disaster not only caused immediate death and injury, but also led to long-term environmental and health impacts that are still affecting the countries and people involved.
The causes of this disaster were complex and far-reaching, involving technical flaws, human errors and systemic safety culture issues.
According to reports, the Chernobyl disaster occurred during a test designed to simulate cooling a reactor in the event of an unexpected power outage. However, due to a design flaw, the test did not go as expected and instead resulted in an intense energy surge. This resulted in ruptured reactor elements, loss of coolant, and a steam explosion and meltdown that destroyed the containment building and spread radioactive material.
Within 36 hours of the explosion, authorities established a 10-kilometer exclusion zone to protect the public, initially evacuating about 49,000 people, which was later expanded to 30 kilometers, for a total of about 68,000 people. The disaster directly caused the deaths of two engineers, dozens of workers were seriously injured and hospitalized, 134 people showed acute radiation symptoms, and 28 of them died within three months.
The impact of the Chernobyl disaster still makes people think deeply. Have we learned any lessons?
The United Nations Scientific Committee estimated that the radiation effects of the Chernobyl accident killed fewer than 100 people. However, estimates of the final death toll vary slightly from institution to institution. For example, a 2006 study by the World Health Organization predicted 9,000 cancer-related deaths in Ukraine, Belarus, and Russia. Faced with such high health risks, the response of the emergency teams at the time was considered catastrophic.
Accident Sequence
Background
Cooling down the reactor after shutdown
In the operation of a nuclear reactor, most of the heat is produced by nuclear fission, but more than 6% comes from radioactive decay heat. This cooling must continue after the reactor is shut down. If the coolant circulation is interrupted, the icy core may overheat and cause a meltdown.
Safety Testing
The Chernobyl accident occurred during a safety test to confirm the performance of the turbine generator. Despite multiple experimental failures, the testing plan is still proceeding as planned.
Unexpected power dropDuring the night hours of 1986, the testing plan called for gradually reducing the reactor power. However, due to the influence of certain reaction products (xenon-135), the power continued to decrease. The operator took a series of incorrect actions in this situation, which ultimately led to the low power state.
The accident happened
Test Execution
After the test began, the reactor should have been operating within its normal operating range, but various improper operations caused the reactor's power to surge nearly tenfold in a short period of time, which ultimately led to a fatal explosion.
Explosion and aftermath
The explosion following the accident released a large amount of radioactive material and caused irreversible damage to the surrounding environment.
The effects of the explosion are not yet fully understood, but it is generally believed that the steam pressure inside the reactor caused a steam explosion, which destroyed the reactor shell and further released a large amount of radioactive material into the environment, causing harm to humans and the ecosystem. had a devastating impact.
The consequences of the Chernobyl nuclear disaster were not only a disaster for a region, but also triggered a global rethinking of nuclear energy safety. Over the past few decades, this incident has brought profound lessons and reflections to relevant countries and the international community. How should we ensure nuclear safety in the future?
