What is Nuclear Fission?
Nuclear fission is the process where the nucleus of a heavy atom, such as uranium-235, splits into two lighter nuclei when struck by a neutron. This releases a tremendous amount of energy, additional neutrons, and radiation. The reaction is exothermic, converting a small portion of the atom's mass into energy according to Einstein's E=mc² equation. It forms the basis for both nuclear weapons and controlled power production.
The Step-by-Step Process of Fission
The process begins when a slow-moving neutron collides with a fissile nucleus, making it unstable and causing it to split. This fission instantly produces 2-3 neutrons, fragments like barium and krypton, and about 200 MeV of energy per event. These neutrons can then trigger further fissions in nearby atoms, creating a self-sustaining chain reaction if moderated properly. Control rods absorb excess neutrons to regulate the reaction rate, preventing explosions.
Practical Example in a Nuclear Reactor
In a pressurized water reactor (PWR), uranium fuel rods are submerged in water, which acts as both moderator and coolant. Neutrons fission uranium atoms, heating the water to produce steam that drives turbine generators for electricity. For instance, a single kilogram of uranium-235 can generate energy equivalent to 2,700 tons of coal, demonstrating fission's efficiency in plants like those in the U.S. nuclear fleet.
Applications in Power Generation and Importance
Nuclear fission powers about 10% of global electricity, providing baseload energy without greenhouse gas emissions during operation. It's crucial for energy security in countries like France, where it supplies over 70% of power. However, challenges include radioactive waste management and safety risks, as seen in incidents like Chernobyl. Advancements in reactor designs aim to enhance safety and sustainability, making fission a key player in the transition to low-carbon energy.