This blog post examines technical and managerial measures to ensure the safety of nuclear power plants, based on the Fukushima and Chernobyl accident cases.
The Fukushima nuclear accident has reignited heated debate about the safety of nuclear power plants. In South Korea, recent revelations of corruption among nuclear industry workers have eroded trust in nuclear power. Coupled with media reports suggesting nuclear plants are unsafe, many South Koreans now feel uneasy. People worry whether South Korea’s nuclear plants could cause a major accident like Japan’s Fukushima disaster.
To get straight to the point: nuclear power plants will never explode like a nuclear bomb due to a typical accident. While there is a possibility of problems occurring in the internal heat transfer system or cooling devices, leading to a rapid pressure increase and explosion, nuclear power plants are structurally completely different from nuclear bombs. Let’s now examine the reasons for this through scientific principles.
Natural uranium primarily exists as two isotopes: uranium-235 and uranium-238. Of these, uranium-235 plays a crucial role in nuclear power generation. Uranium-235 is a highly unstable element; when struck by an external neutron, it undergoes nuclear fission, releasing enormous amounts of energy. This energy is precisely what is harnessed in reactors to generate electricity. It is this natural fission property of uranium-235 that makes it suitable as nuclear fuel for power generation.
The principle of a ‘chain reaction’ is crucial for nuclear power generation. This occurs when neutrons produced during fission collide with other uranium-235 atoms, triggering a continuous sequence of fission reactions. A chain reaction is often likened to the sequential toppling of dominoes. Just as dominoes fall at regular intervals, influencing each other, the fission of uranium-235 occurs sequentially through collisions with neutrons. However, just as dominoes placed too far apart cannot knock down the next one, a low concentration of uranium-235 prevents the chain reaction from continuing. Nuclear power plants therefore strictly control uranium concentration to maintain a stable chain reaction.
Naturally occurring uranium-235 constitutes only about 0.7% of total uranium, a very small amount. This concentration is insufficient to sustain a sufficient chain reaction. Therefore, to use it in reactors, uranium-235 undergoes an ‘enrichment’ process to raise its concentration to approximately 3-5%. This ensures a stable chain reaction at the appropriate concentration, suppressing excessive fission within the plant and enabling safe electricity generation. However, even during this process, the uranium concentration never reaches the levels used in nuclear bombs—over 90%—so there is no risk of explosion.
What would happen in the worst-case scenario where external power is lost and the cooling system fails at a power plant? In this case, the reactor temperature could rise sharply, but a nuclear explosion would not occur. Even if an excessive chain reaction occurs inside the reactor, the fission rate naturally decreases due to a physical effect called ‘Doppler broadening’. Doppler broadening is a phenomenon where the decay effect of uranium-235 nuclei at high temperatures cannot be transmitted to neighboring atoms, thereby spontaneously regulating the chain reaction. In other words, reactors are designed to suppress nuclear fission once temperatures exceed a certain level, maintaining stability to prevent further temperature increases.
Now, let’s examine the specific cause of the Fukushima nuclear accident. The 2011 Fukushima nuclear accident occurred when the plant’s cooling system failed due to an earthquake and tsunami, causing fuel rods to overheat and release radioactive material. It was not a reactor explosion; rather, seawater injected for cooling became contaminated water containing radioactive material, which then spread radioactive substances into the sea and air. The core issues were material damage and radioactive leakage caused by overheating inside the plant, not an explosion like an atomic bomb.
The Chernobyl nuclear accident occurred under a similar principle. The 1986 Chernobyl accident happened when attempts to artificially increase reactor output caused cooling water to vaporize, leading to a rapid rise in internal pressure. The Chernobyl accident also involved damage to the cooling system due to a rapid temperature increase, leading to a massive leak of radioactive material. While this accident caused severe radioactive contamination, it was not an explosion like a nuclear bomb.
Following these two accidents, nuclear researchers added various safety devices and improved existing reactor designs, implementing diverse measures to prevent rapid chain reactions even during emergencies. They particularly developed technologies to withstand external impacts, such as seismic-resistant design, and built redundant safety devices and automated control systems to enhance the reliability of cooling systems. South Korea’s nuclear power plants are also strictly managed according to these strengthened design standards.
However, technical safety alone is insufficient to alleviate public anxiety about nuclear power plants. Citizens must have confidence that nuclear power plants are operated transparently and thoroughly, free from corruption. The safety of nuclear power plants is only complete when both mechanical stability and managerial stability are secured. To achieve this, trust must be instilled in the public through rigorous anti-corruption measures, strict management oversight, and periodic safety inspections.
Through such efforts, we must prevent the recurrence of accidents like Fukushima or Chernobyl and establish an energy supply system that reassures the public. To this end, nuclear researchers worldwide are strengthening earthquake-resistant reactor designs and seawater intrusion countermeasures, while developing new safety devices capable of controlling nuclear fission. If these safety measures continue to improve, nuclear power can be safely utilized as a vital energy resource.
