%A"Mankamo, T [Avaplan Oy, Espoo (Finland)]" %A"Poern, K [Studsvik Nuclear (Sweden)]" %A"Holmberg, J [Valtion Teknillinen Tutkimuskeskus, Espoo (Finland). Saehkoe- ja Automaatiotekniikan Lab.]" %D1991 %I; Valtion Teknillinen Tutkimuskeskus, Espoo (Finland) %2 %J[] %K99 GENERAL AND MISCELLANEOUS//MATHEMATICS, COMPUTING, AND INFORMATION SCIENCE, 21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS, BWR TYPE REACTORS, RISK ASSESSMENT, NUCLEAR POWER PLANTS, PROBABILITY, REACTOR SAFETY, RELIABILITY, SYSTEM FAILURE ANALYSIS, 990200, 210100, MATHEMATICS AND COMPUTERS, POWER REACTORS, NONBREEDING, LIGHT-WATER MODERATED, BOILING WATER COOLED %PMedium: X; Size: 46 p. %TUses of risk importance measures. Technical report %XRisk importance measures provide an understandable and practical way of presenting probabilistic safety analysis results which too often tend to remain abstract numbers without real insight into the content. The report clarifies the definitions, relationships and interpretations of the three most basic measures: Risk increase factor, risk decrease factor, and fractional contribution. The above three measures already cover the main types of risk importance measures. Many other importance measures presented in literature are close variants to some of these three measures. They are related in many cases so that, for a technical system considered, the two other measures can be derived from the one calculated first. However, the practical interpretations are different, and hence each three measures have their own uses and rights to existence. The fundamental aspect of importance measures is, that they express some specific influence of a basic event on the total risk. The basic failure or error events are the elements from which the reliability and risk models are constituted. The importance measures are relative, which is an advantage compared to absolute risk numbers, due to insensitivity with respect to quantification uncertainties. Therefore they are particularly adapted to give first hand guidance where to focus main interest from the system`s risk and reliability point of view and wherefrom to continue the analysis with more sophisticated methods requiring more effort. %0Technical Report %NVTT-TIED-1245;Other: ON: DE92613012; ISBN 951-38-3877-3; TRN: FI9100124009225 %1 %CFinland %Rhttps://doi.org/ Other: ON: DE92613012; ISBN 951-38-3877-3; TRN: FI9100124009225 FIN %GEnglish