Nuclear power plants are designed to keep the concentration of uranium tightly controlled to prevent a nuclear bomb-like explosion. In the Fukushima and Chernobyl accidents, where radioactive material leaked due to a damaged cooling system, safeguards have been strengthened in recent years. However, in addition to technical safety, transparent operations and the prevention of corruption are important for public trust.
The Fukushima nuclear disaster has reignited the debate on the safety of nuclear power plants. In South Korea, the recent revelations of corruption among nuclear workers have led to a decline in the trustworthiness of nuclear power plants, and many South Koreans are feeling uneasy about the safety of nuclear power plants as well as reports on television that nuclear power plants are unsafe. People are worried about the possibility of a major accident at a Korean nuclear plant like the one in Fukushima, Japan.
The bottom line is that nuclear power plants never explode like a nuclear bomb in a typical accident. Of course, there is a chance that something could go wrong with the internal heat transfer system or cooling system, causing the pressure to rise rapidly and explode, but a nuclear power plant is structurally completely different from a nuclear bomb. Now let’s look at the science behind why.
In nature, uranium exists mainly in two isotopes: uranium-235 and uranium-238. Of these, it’s uranium-235 that plays an important role in nuclear power generation. Uranium-235 is a highly unstable element, and when it is bombarded by neutrons from the outside, it fission and releases a tremendous amount of energy. This energy is what reactors use to generate electricity. It is this natural fissile property that allows uranium-235 to be used as nuclear fuel for nuclear power generation.
Nuclear power generation relies on a principle called the “chain reaction,” in which neutrons produced during fission are bombarded by other uranium-235, triggering a cascade of fission reactions. The chain reaction is often analogized to a series of falling dominoes. Just as dominoes fall at regular intervals and affect each other, the fission of uranium-235 occurs sequentially through collisions with neutrons. However, just as dominoes that are too far apart cannot knock down the next domino, the chain reaction cannot continue if the concentration of uranium-235 is too low. In other words, nuclear power plants closely control the concentration of uranium to keep the chain reaction stable.
In nature, the amount of uranium-235 is very small, about 0.7% of total uranium. This concentration is insufficient to produce a sufficient chain reaction, so to use it in a reactor, uranium-235 is “enriched” to increase its concentration to about 3-5%. This ensures that a stable chain reaction is maintained at the right concentration, and that the excessive fission that occurs inside the plant is contained and electricity can be generated safely. However, even during this process, the uranium does not reach the concentration used in nuclear bombs, i.e., more than 90%, so there is no possibility of an explosion.
What happens in the worst case scenario, when the plant loses external power and the cooling system stops working? In this case, the temperature of the reactor may rise rapidly, but a nuclear explosion is unlikely to occur. Even if the chain reaction inside the reactor becomes excessive, the fission rate will naturally slow down thanks to a physical effect called ‘Doppler broadening’. Doppler broadening is a phenomenon that prevents the nuclei of uranium-235 atoms from transmitting their decay effects to neighboring atoms at high temperatures, which results in a self-regulating chain reaction. In other words, the reactor is designed to be stable beyond a certain temperature, where fission is inhibited and no further temperature increase is possible.
Now, let’s look at the specific causes of the Fukushima nuclear accident. The 2011 Fukushima nuclear disaster occurred after an earthquake and tsunami caused the plant’s cooling system to fail, causing fuel rods to overheat and leak radioactive material. The reactors didn’t explode, but the seawater that was used to cool the plant turned into contaminated water containing radioactive material, spreading radioactivity into the sea and air. The problem was material breakdown and radioactive leakage due to overheating inside the plant, not an atomic bomb-like explosion.
The Chernobyl nuclear accident occurred on a similar principle. The 1986 Chernobyl accident was caused by an attempt to artificially increase the power of the reactor, causing the coolant to vaporize and the internal pressure to rise rapidly. In this case, the reactor itself did not explode, but the rapid rise in temperature damaged the cooling system and caused a massive leak of radioactive material. While the accident resulted in significant radioactive contamination, it was not a nuclear bomb-like explosion.
Since these two accidents, nuclear researchers have added a number of safeguards and improved the design of existing reactors to prevent a rapid chain reaction in the event of an emergency. In particular, they have developed technologies to prepare for external shocks, such as earthquake-resistant designs, and have built redundant safeguards and automatic control systems to increase the reliability of cooling systems. South Korea’s nuclear power plants are also thoroughly managed according to these enhanced design standards.
However, it takes more than technical safety to address public anxiety about nuclear power plants. People need to trust that nuclear power plants are operated transparently and thoroughly, without any irregularities. The safety of nuclear power plants is not just about mechanical reliability, but also about managerial reliability. This requires thorough crackdowns on corruption, strict management oversight, and periodic safety inspections to instill trust in the public.
These efforts are necessary to prevent the recurrence of accidents like Fukushima and Chernobyl, and to ensure a reliable energy supply system. To this end, nuclear researchers around the world are strengthening reactor seismic design and seawater intrusion preparedness, and developing new safeguards to control nuclear fission. As these safety measures continue to improve, nuclear power can be safely used as an important energy resource.
