Preliminary safety analysis of the 2400 MWth gas-cooled fast reactor

The present paper is dedicated to the preliminary safety analysis of the Gas Fast Reactor (GFR2400). In a first part of the paper, the safety objectives and the governing principles of the safety approach are briefly presented. The general frame includes the defense in depth principle, the principle of physical barriers whose protection is insured by the fulfillment of the safety functions. The approach proposed includes the use of probabilistic assessments of accidental and incidental sequences when it is relevant in a so-called risk-informed methodology. The transient analysis, performed thanks to the CATHARE2 code and whose some illustrative results are presented in this paper, permitted to assess the provisions foreseen in order to cope with the acceptance criteria of the reactor as well as to assess the reliability of the DHR system and of the associated accidental operating of the reactor. Several single aggravating failures have been considered in the calculations. Among these failures, those inducing the most adverse effects have been retained as reference cases of the safety assessment and are presented in the paper. Furthermore, the behaviour of the reactor has been investigated in case of more complex sequences including the cross failure of systems in order to assess the robustness of the safety provisions as well as to assess the possibility to control slow depressurization scenarios with passive back-up systems. The design improvements already brought out thanks to the 'design-orientated' probabilistic study under way are put in evidence in the paper. These improvements illustrate how the PSA and the classical safety analysis can be fed by each other in order to obtain an overall efficient preliminary safety analysis. Finally a methodology is proposed to identify and to classify the possible severe accidents situations. (authors)