In this blog post, we will look at the technical and administrative measures to ensure the safety of nuclear power plants based on the cases of the Fukushima and Chernobyl accidents.
The Fukushima nuclear accident has reignited the debate over the safety of nuclear power plants. In South Korea, the recent revelation of corruption among nuclear power industry workers has lowered the public’s confidence in nuclear power plants, and reports on the dangers of nuclear power plants on television have left many South Koreans feeling anxious. People are concerned that South Korea’s nuclear power plants are just as likely to cause a major accident as Japan’s Fukushima nuclear power plant.
To cut to the chase, it is impossible for a nuclear power plant to explode like a nuclear bomb due to a general accident. Of course, there is a possibility that the pressure will rise rapidly and explode due to a problem in the internal heat transfer system or cooling system, but a nuclear power plant is structurally completely different from a nuclear bomb. Now, let’s take a look at the scientific principles behind this.
Uranium in its natural state exists mainly in two isotopes: uranium-235 and uranium-238. Of these, uranium-235 plays an important role in nuclear power generation. Uranium-235 is a very unstable element that releases enormous amounts of energy when a neutron collides with it, causing nuclear fission. This energy is used to generate electricity in nuclear reactors. It is this natural fissionable property of uranium-235 that makes it suitable as nuclear fuel for nuclear power generation.
The principle of “chain reaction” is important for nuclear power generation, in which neutrons generated during nuclear fission collide with other uranium-235, causing a continuous fission reaction. The chain reaction is often likened to a series of dominoes falling over. Just as dominoes fall over at regular intervals and affect each other, the fission of uranium-235 occurs in sequence through collisions with neutrons. However, if the dominoes are too far apart, the next domino cannot be knocked over, and if the concentration of uranium-235 is low, the chain reaction will not continue. In other words, nuclear power plants are maintaining a stable chain reaction by strictly controlling the concentration of uranium.
Natural uranium-235 is very small, accounting for only 0.7% of all uranium. This concentration is not enough to cause a chain reaction, so in order to use it in a nuclear reactor, the uranium-235 must be enriched to a concentration of about 3-5%. This maintains a stable chain reaction at the appropriate concentration, suppressing the excessive fission that occurs inside the power plant and allowing it to generate electricity safely. However, even in this process, the concentration of uranium does not reach the concentration used in nuclear bombs, i.e. 90% or more, so there is no possibility of an explosion.
What would happen if the worst-case scenario occurred, where the power supply is cut off from the power plant and the cooling system stops working? In this case, the temperature of the reactor may rise rapidly, but it will not cause a nuclear explosion. Even if a chain reaction occurs excessively inside the reactor, the rate of fission will naturally decrease thanks to a physical effect called “Doppler broadening.” The Doppler effect is a phenomenon in which the nucleus of uranium-235 prevents the decay effect from being transmitted to neighboring atoms at high temperatures, thereby spontaneously controlling the chain reaction. In other words, the reactor is designed to maintain stability by suppressing nuclear fission when the temperature exceeds a certain level so that the temperature no longer rises.
Now, let’s take a look at the specific causes of the Fukushima nuclear accident. The 2011 Fukushima nuclear accident was an accident in which radioactive materials leaked due to the failure of the plant’s cooling system due to an earthquake and tsunami, causing the fuel rods to overheat. The reactor did not explode, but the seawater used to cool it turned into contaminated water containing radioactive materials, which spread radioactive materials into the sea and air. The problem was material damage and radioactive leakage due to overheating inside the power plant, and it was not an explosion like an atomic bomb.
The Chernobyl nuclear power plant accident occurred under a similar principle. The 1986 Chernobyl accident occurred when the cooling water vaporized and the internal pressure rose sharply as the reactor was artificially increased. The Chernobyl accident was also not caused by the explosion of the reactor itself, but by a rapid rise in temperature that damaged the cooling system and caused a massive leak of radioactive material. This accident caused serious radioactive contamination, but it was not an explosion in the same way as a nuclear bomb.
After these two accidents, researchers in the nuclear power industry added various safety devices and improved the design of existing reactors to prevent a chain reaction from occurring rapidly in the event of an emergency. In particular, they have developed technologies to prepare for external shocks, such as earthquake-resistant design, and have built redundant safety devices and automatic control systems to increase the reliability of the cooling system. South Korea’s nuclear power plants are also being thoroughly managed in accordance with these enhanced design standards.
However, technological safety alone is not enough to alleviate the public’s anxiety about nuclear power plants. The public must have confidence that nuclear power plants are being operated transparently and thoroughly without corruption. The safety of nuclear power plants is complete when not only mechanical stability but also administrative stability is secured. To do this, the public must be instilled with confidence through strict anti-corruption measures, strict management and supervision, and periodic safety inspections.
Through such efforts, we must prevent the recurrence of accidents like Fukushima and Chernobyl and establish an energy supply system that can provide reassurance to the public. To this end, nuclear researchers around the world are strengthening the seismic design of nuclear reactors and countermeasures against seawater intrusion, and are developing new safety devices that can control nuclear fission. If these safety measures continue to be improved, nuclear power will be able to be used safely as an important energy resource.
