For each of the reactor lines considered (pressurized water reactors, pressurized light water cooled heavy water moderated reactors, high temperature gas cooled reactors, sodium cooled and lead cooled fast reactors, and non-conventional designs), the design features contributing to different levels of defence in depth are summarized and structured as described below.

The first five tables for each reactor line give a summary of design features contributing to Level 1 through Level 5 of defence in depth with a short explanation of the nature of these contributions, in line with the definitions given in [7]. Passive and active safety systems are highlighted in more detail in conjunction with Level 3 defence in depth.

It should be noted that original safety design concepts of the considered SMRs do not always follow the defence in depth concept recommended in by IAEA safety standards [7]. Although all designers were requested to follow the recommendations of [7] when providing descriptions of SMR safety design features enclosed as Annexes I-X, the results are non-uniform. For example, some Level 4 features were in several cases attributed to Level 5 for PWRs, etc. To provide a uniform basis for descriptions, the attribution of safety design features to certain levels of defence in depth was harmonized for all SMRs considered, following the recommendations of [7], and in this way presented in all tables of this section. Therefore, attribution indicated in the tables below may be in some cases different from that originally provided by designers in the corresponding annexes.

The sixth table for each reactor line summarizes the degree of detail in the definition of design basis and beyond design basis events, as observed in the corresponding annexes, and highlights the events specific to a particular SMR, but not to the corresponding reactor line.

The seventh table gives a summary of deterministic and probabilistic acceptance criteria for design basis and beyond design basis events as applied by the designers, and specifically highlights cases when a risk — informed approach is being used or targeted.

The eighth table for each reactor line summarizes design features for plant protection against external event impacts, with a focus on aircraft crashes and earthquakes, and refers to recent IAEA publications of relevance [6], when applicable.

Finally, the ninth table gives a summary of measures planned in response to severe accidents.

The final paragraph in each of the following subsections provides a summary of safety design approaches pursued by designers of SMRs, using the above mentioned tables as references, with a link to IAEA safety standards [7] and other publications of relevance.