What keeps radioactive material inside a nuclear power plant?
Nuclear safety does not rely on one perfect wall or one perfect operator. The basic idea is multiple physical barriers plus independent and redundant systems, procedures and emergency planning.
Fuel and fuel cladding
Fuel pellets sit inside sealed metal tubes. The cladding is the first major physical barrier around fission products.
Reactor coolant pressure boundary
The reactor vessel and connected coolant system form another robust boundary around the reactor coolant and core.
Containment
A reinforced containment structure surrounds the reactor system and is designed to limit releases if earlier barriers are challenged.
Defense in depth
Physical barriers are only part of the safety strategy. Regulators also use redundant and diverse safety functions, trained operators, monitoring, testing, access controls and emergency response.
Barrier ≠ safety system ≠ emergency plan.
Barriers
Cladding, coolant boundary and containment are physical boundaries intended to keep radioactive material isolated.
Safety functions
Shutdown, cooling, power and monitoring systems are designed with redundancy or diversity depending on the plant and regulation.
Procedures & response
Training, inspections, maintenance and emergency preparedness add further layers beyond hardware.