Assumption and analysis on catastrophic event by setting scenario under various uncertainties

This paper deals with a concept of the worst scenario as an initial condition and boundary conditions to simulate how an event is going to develop mainly related to the safety problem. Some twenty years ago, the worst scenario was decided very subjectively under the limited CPU time of an available computer. The author wants to discuss how to get the worst scenario under uncertainties logically and related matters. Comparison of Fault Tree and Event Tree methods as well as Monte Carlo method has been discussed. And the concept of craziness, that is, fuzziness with fluctuation, is discussed also. The author will try to discuss such various procedures for setting up the 'scenario' for the simulation on disasters, both a man-induced event or a natural event more logically than the subjective approach