[en] This report proposes an environmental review of the content of a request for the modification of the decree authorizing the creation of the 'Georges Besse' INB 93 (basic nuclear installation), a uranium enrichment plant exploited by EURODIF-production on the Tricastin site. This modification notably deals with the PRISME operation. The report describes and discusses the objectives of this operation, its context and the concerned operation program. It indicated the concerned procedures. It discusses the style and content of the impact study from a general point of view, and outlines weaknesses and methodological problems. It more particularly discusses the analysis of the present site condition, the project presentation and justification, the analysis of impacts on the environment and on health, of impacts related to waste management, of non-radiological impacts on water, of impacts on air and on biodiversity, and of social and economic impacts. It also addresses the analysis of impacts of construction works. It finally discusses the analysis of the risk management study