Review of quantitative accuracy assessments with fast Fourier transform based method (FFTBM)

In the past 10 years various methodologies were proposed to evaluate the uncertainty of BE code predictions. One common step to all methodologies is the use of experimental and plant data for the nodalization development and qualification. When thermal–hydraulic computer codes are used for simulation the questions raised are: ‘How long improvements should be added to the model, how much simplification can be introduced and how to conduct an objective comparison?’ The proposed fast Fourier transform based method (FFTBM) assists in answering these questions. The method is easy to understand, convenient to use, user independent and it clearly indicates when simulation needs to be improved. The FFTBM shows the measurement–prediction discrepancies—accuracy quantification—in the frequency domain. The acceptability factor for code calculation was determined based on several hundreds of code calculations. The FFTBM method has been applied to various international standard problems, standard problem exercises and other experiment simulations that are presented in the paper. The result shows that the quantitative comparison between thermal–hydraulic code results and experimental measurements with qualitative evaluation may assist the decision whether or not the simulation needs to be improved.