[en] The expert judgment process used in NUREG--1150, ''Severe Accident Risks: An Assessment for Five US Nuclear Plants,'' is an advance over those processes developed in previous probabilistic risk assessments. The new process was used to obtain expert judgment on issues expected to be the main contributors to the potential risk of five nuclear plants. The use of expert judgment helped to incorporate both the experience and the research results obtained since the Reactor Safety Study (US NRC, 1975). The new process also enabled NUREG--1150 to include a comprehensive uncertainty analysis, an analysis that had been lacking in the earlier Reactor Safety Study. This process for gathering expert judgment was developed in response to criticisms applied to the previous Reactor Safety Study by the Lewis Committee (Lewis, 1978) and to review comments of the Kouts Committee (1987) on the draft NUREG--1150. The process is based on accepted decision analysis techniques and findings from the numerous studies involving the quantification of judgment. The result, a formal process for eliciting and documenting expert judgment for risk assessment, is one of the major contributions of NUREG-1150. 19 refs., 5 figs., 1 tab