Series of articles on barriers 1/6: Barriers protect people and the environment from radioactive substances

The barrier concept aims to trap sources of radiation in nuclear facilities across several levels. Similar to the layers of an onion, independent barriers ensure that the risk from sources of radiation are minimised for people and the environment.

The barrier concept for the Swiss nuclear power plants consists of a series of three physical barriers to trap the radioactive substances present in the nuclear fuel.

Sequence of three barriers

  • Barrier 1: Fuel assemblies
  • Barrier 2: Primary circuit
  • Barrier 3: Containment

The fuel assemblies form the first barrier. The primary circuit is referred to as the second barrier. This, in turn, is enclosed by the containment as the third barrier. You can find more information on the barriers in the other articles in this series.

Safety and Security

These barriers are staggered and independent of one another. Even if one barrier partially or completely fails due to an incident, the remaining barriers ensure that no radioactive substances enter the environment.

Safety precautions taken by Swiss nuclear power plants

The barrier concept is not a complete safety concept. Rather, it represents one part of the safety precautions. The safety precautions taken by Swiss nuclear power plants can be considered from two perspectives: one perspective is the concept of defence in depth, the other is the concept of protection objectives.

Protection objectives

The following three protection objectives must be complied with to protect people and the environment from ionising radiation:

Control the reactivity

Cool the fuel assemblies

Trap radioactive substances

Compliance with these three protection objectives ultimately pursues the following overarching protection objective:

Limit radiation exposure

All aspects of the safety precautions can be assigned to the two perspectives. The barrier concept is also part of both perspectives.


This is the first of six articles on the topic of barriers for trapping radioactive substances. The next five articles provide a more detailed description of the barriers.