Our goal is to evaluate validity of numerical simulation results in the nuclear field in order to estimate real behavior of nuclear plants and thus to contribute their security and safety. Recently, it becomes possible to execute a full-scale numerical simulation under a real condition, such as a seismic behavior of entire nuclear plant. To estimate real behavior accurately by such simulations, it is indispensable to evaluate validity of simulation results because numerical simulations include various uncertainties such as “uncertainty due to randomness” and “uncertainty due to lack of knowledge”. As one of approaches to evaluate validity of simulation results, we introduce “the degree of certainty” of simulations to real behavior. Here, to get a more accurate degree of certainty, we try to confirm the degree of influence about unevenness of uncertainty and to reduce uncertainty due to lack of knowledge. For this, we research and develop a validity evaluation system composed of three tools. One is a tool able to introduce the degree of certainty from various uncertainties to put together various uncertainties. Another is a tool able to analyze the sensitivity of each uncertainty to whole uncertainty. Moreover, we research a tool able to analyze factors of various uncertainties. We have applied them to our seismic simulation system which enables to execute the assembly structure analysis of an entire nuclear plant and confirmed that their functions are applicable to the simulation.

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