Worth assessments in risk level analysis for industrial installations

In the last years, as a consequence of the technological expansion, a set of techniques which allow describing of a complex system, the associated probabilities quantification, the identifying of psychic and physical consequences of a such a system and their quantification have been developed. The system failure causes and consequences knowledge allows a safety level assesment. This can be achieved by means of probabilistic safety assesment (PSA). After such an analysis one can make decision for establishing the safety acceptable level and for choosing of optimal strategies to reduce the risk. The PSA applications assure the knowledge base for these decision makings. The paper presents an essential category of PSA applications, the assessments of importance: the risk achievement worth of a function (RAW), the risk reduction worth (RRW), the cumulated contribution of a base event to risk level (Fussel and Vesely). The methodology is illustrated by a system analysis, the studied objectives being the system of isolation group column CL301 from the pilot plant of heavy water production of ICSI (ex Plant 'G') Rm Valcea. (authors)