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5 Conclusions and General Comments
Pages 36-44

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From page 36...
... it has no overarching risk assessment framework to ensure the consistency and logic of the analyses; (2) it lacks a clear description of how the models were implemented, how the probabilities were calculated, and how the results were reached; (3)
From page 37...
... Stakeholder participation took the form of a highly interactive and cooperative PWS steenng committee comprised of representatives of various subcommunities interested in, and affected by, the PWS TAPS trade. "Unanimous approval for all decisions taken by the PWS steering committee was required.
From page 38...
... . CANDIDATE RISK REDUCTION MEASURES The PWS Study team, including the PWS steering committee, attempted to be exhaustive and to get their compilation of (community-supplied)
From page 39...
... Fault trees are generally used to compute the probabilities of subsystem failures as part of an overall event tree analysis. Fault trees show the logical links between occurrences of basic events and occurrences of the top event through Boolean relationships; computation of the probability of the top event is a function of the probabilities of the basic events.
From page 40...
... Because the accident frequency in PWS was very low, the study team established a "ground truth" against which to compare the analytic results, which added to the uncertainty. Because of the constant interaction of the PWS Study team and PWS steering committee, the NRC committee concluded that the steering committee was, in effect, part of the study team and that the study was conducted jointly.
From page 41...
... , could be done more effectively and at less cost. The PWS Study represents considerable efforts by the two contractors of the study team, who were assisted on a regular basis by the PWS steering committee.
From page 42...
... EXPANDED CRITERIA Is there a clear statement of the constraints placed on the study team and of the impacts of these constraints? In briefings to the NRC committee, the PWS Study team mentioned some constraints, such as the exclusion of the effects of earthquakes, that are also mentioned In the study, although the impact of these constraints is not discussed.
From page 43...
... This NRC review committee has identified many weaknesses that should be brought to the attention of the PWS steering committee and any other group evaluating the usefulness of He PWS Study. If this approach were used elsewhere, the scope of the study should be expanded to include other outcomes, such as loss of life and damage to a broader class of vessels.
From page 44...
... The PWS Study is a significant step forward in the use of probabilistic methods in marine risk analysis, even though, in the judgment of the NRC committee, it is not complete and should not be replicated. But if the weaknesses identified in this NRC review report are addressed, a systems approach based on Me PWS Study could be used to analyze risks in other marine systems.


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