II — 4.1. List of design basis and beyond design basis accidents

Table II-2 summarizes the main inherent safety features of IRIS, stemming from its safety-by-design™ approach [II-3], together with their implication on design basis events (listed in the fourth column) typically considered by the US NRC for PWRs.

Preliminary list of initiating events for beyond design basis accidents:

• Hypothetical reactor pressure vessel break;

• A transient with failure of all safety systems.

II — 4.2. Acceptance criteria

The deterministic acceptance criteria for design basis accidents (DBAs) are assumed to be the same as for conventional PWRs with a note, that de facto most of the DBAs in IRIS would be either eliminated or downgraded via a safety-by-design™ approach [II-3], see Table II-2.

The deterministic acceptance criteria for beyond design basis accidents (BDBA) in IRIS, defined on a preliminary basis, include in-vessel retention by passive means.

The probabilistic acceptance criteria for BDBA in the IRIS are summarized in Table II-3.