Collectively, the multi-barrier system provides the following safety functions:

S1: Isolation of radioactive waste from humans and the environment;

S2: Complete containment of radionuclides for a period of time;

S3: Immobilisation, retention, and slow release of radionuclides;

S4: Compatibility of the components of the repository system;

S5: Long-term stability of the multi-barrier system with regard to long-term geological and climatic evolution.

These safety functions are used to derive a set of safety requirements on the system components, including the “pillars of safety” described below. In the current repository design the safety functions are provided by the elements of the multi-barrier system. Future changes to the system remain possible as there is no single solution for how to provide these safety functions.

Performance assessment, carried out as part of the safety assessment, analyses whether the barriers perform their various functions and thus fulfil their assigned safety functions. Performance assessment is described further in Chapter ‎6.