A prerequisite for the use of nuclear energy is ensuring the safety of the environment during both normal operation and emergencies.
Assurance of nuclear safety is based on general principles that have been formed by experience and research. According to these principles, safety is ensured by so-called defence in depth and multiple arrangements. A dangerous situation can arise only if several defects and errors by operating personnel occur at the same time.
Shutting down and placing the reactor into a safe state in connection with an accident or a breakdown require that safety systems are operational. The design and dimensioning of safety systems are based on computational accident analyses and experimental data.