There is much more uranium- 235 in a typical nuclear power plant than there was in the bomb that destroyed the city of Hiroshima. Why can't the reactor explode like an atomic bomb?

Nuclear power plants and atomic bombs both use uranium-235 as fuel, but the concentration is different. In nuclear power plants, the concentration of uranium-235 is only about 3-5%, while in atomic bombs, it is more than 90%. More concentrated uranium-235 in the atomic bomb allows for a faster, more uncontrollable chain reaction.

Both nuclear power plants and atomic bombs create energy through induced fission, breaking uranium-235 nuclei by bombarding them with neutrons. This process releases energy as well as more free neutrons, which can then collide with other uranium-235 nuclei, creating a chain reaction. In a nuclear power plant, a continuous reaction is necessary to generate electricity, but the reaction needs to be controlled to avoid overheating or explosion.

The control and moderation of the chain reaction are essential in a nuclear power plant. This is achieved by using control rods made of materials that absorb neutrons, slowing down the reaction when needed. By adjusting the position of these control rods, operators can manage the rate of reactions. In contrast, atomic bombs have no such moderation or control system, allowing the reaction to proceed uncontrolled, resulting in an explosion.

Nuclear power plants are designed to operate with a subcritical mass of uranium-235, where the percentage of neutrons that cause further reactions is lower than the number of neutrons emitted. This prevents an exponential increase in reactions and keeps the power plant under control. On the other hand, atomic bombs are designed with a supercritical mass of uranium-235, which allows for an exponential increase in reactions and a release of a massive amount of energy in an explosion. In conclusion, a nuclear power plant cannot explode like an atomic bomb due to the differences in the concentration of uranium-235, the control mechanisms for chain reactions, and the critical mass of the fuel. The careful design and operation of nuclear power plants ensure that the reaction is controlled and sustained, preventing the possibility of an explosion.