shielding

Nuclear reactors generate energy through nuclear fission, a process where atomic nuclei split, releasing neutrons and energy. This creates a self-sustaining chain reaction. Operating reactors produce highly penetrating radiation, including neutrons and gamma rays, from fission and radioactive decay.1

To protect personnel, reactors are surrounded by shielding. This can be a deep pool of water, as in "swimming pool" reactors, or a thick concrete structure called a biological shield. Heavy metals like lead or steel, or heavy aggregates in concrete, are sometimes added to the shielding for more effective absorption of gamma rays.1

Reactors also have containment systems, typically a robust, airtight building designed to prevent the release of radioactivity into the environment, even during severe accidents. These structures must withstand pressure and damage, and protect internal components from external forces.2