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SAFETY FEATURES AND SYSTEMS

The safety of a nuclear power plant is based on the multi-stage “in-depth concept”, the aim of which is to ensure that radioactivity isolation barriers are always in working order.

The first stage is the planning and construction of the components and functions of a nuclear power plant in accordance with high quality requirements and adequate safety margins. Secondly, it is assumed that components may nevertheless fail or that operators can make mistakes, which is why the plant is equipped with protective systems and components. In the event of an operating transient, they endeavor to restore the plant to a safe state. The third stage of the in-depth concept consists of the safety systems, which will mitigate the effects of a possible accident.

Several independent, redundant systems

The reliability of safety-significant functions is guaranteed by means of multiple parallel components and systems (redundancies). The instrumentation and control of safety systems as well as their supply of electricity are kept isolated from the systems used for the normal operation of the plant. The systems performing the most important safety functions must be able to carry out their functions even if an individual component in any system fails and any component affecting the safety function is simultaneously inoperable due to repair or maintenance.

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The operational reliability of the safety functions is determined by means of reliability analyses. In probabilistic safety assessments, the plant is modeled in detail in order to reveal all functional dependencies of the systems. The reliability analyses assist in determining the effect of the plant’s components and functions on overall safety.

Attention to safety at a nuclear power plant means minimizing the risk that the plant causes to its environment. The acronym ALARA is often used in connection with radiation risks. It means operating in such a way that the radiation doses caused to both people at the plant and to the surrounding population are kept As Low As Reasonably Achievable. Correspondingly, safety is also observed under the SAHARA principle: Safety As High As Reasonably Achievable.