ASTRID is the French Advanced Sodium Technological Reactor for Industrial Demonstration which is intended to prepare the Generation IV reactor, with strong improvements in safety and operability.

In this frame, the ASTRID project integrates innovative options. In the earlier phase of ASTRID project, a specific safety approach was set. Main orientations have been examined by the French Nuclear Safety Authority, and the pursuit of the project following these guidelines has been agreed. This basic safety guide is currently applied as reference for the choices of the design options and for safety studies, among other studies regarding hypothetical situations.

Thus, in the frame of ASTRID safety approach, analyses are devoted to well define and study hypothetical situations, which include:

- A domain of accidental sequences with very low occurrence frequency for which severe accident can reasonably be prevented thanks to appropriate design provisions: the domain of severe accident prevention situations (SP);

- Despite the high level of prevention of severe accident implemented in ASTRID, its safety approach postulates also a hypothetical severe accident, in order to comply with the defense-in-depth principle (fourth level) and to check that the induced potential consequences are suitably mitigated: the domain of severe accident mitigation situations (SM);

- A few hypothetical situations, whose consequences could not be reasonably mitigated, and consequently requiring a robust specific safety demonstration, in terms of prevention. These situations have to be “practically eliminated”.

In a first main part, the paper presents:

- The definition of “practically eliminated situations” (SPE),

- The approach used to identify these situations in an exhaustive way,

- The list of “practically eliminated situations” for ASTRID project, issued from the previous methodology.

The second part of the paper focuses on the design impact of the need to practically eliminate one of the identified situations: the “brutal failure of supporting core structures”. The consequences on the structures, involved in the demonstration, are presented (in terms of design, preventive provisions and monitoring means implemented).The paper thus presents the reactor design evolutions to take into account the practical elimination of this situation.

These evolutions represent improvements in relation to past projects.