Regional Basic Professional Training Course in Korea

Regional Basic Professional Training Course (BPTC) on Nuclear Safety
(2) Best‐Estimate Methodology
A best‐estimate model should provide a realistic calculation of the important parameters
associated with a particular phenomenon to the degree practical with the currently
available data and knowledge of the phenomenon. The model should be compared with
applicable experimental data and should predict the mean of the data, rather than
providing a bound to the data. The effects of all important variables should be considered.
If it is not possible or practical to consider a particular phenomenon, the effect of ignoring
this phenomenon should not normally be treated by including a bias in the analysis
directly, but should be included as part of the model uncertainty. The importance of
neglecting a particular phenomenon should be considered within the overall calculational
uncertainty.
Careful consideration should be given to the range of applicability of a model when used
in a best‐estimate code. When comparing the model to data, judgments on the
applicability of the data to the situation that would actually occur in a reactor should be
made. Correlations generally should not be extrapolated beyond the range over which
they were developed or assessed. If the model is to be extrapolated beyond the conditions
for which valid data comparisons have been made, judgments should be made as to the
effect of this extrapolation and the effect should be accounted for in the uncertainty
evaluation. The fundamental laws of physics, well‐established data bases (e.g., steam
tables), and sensitivity studies should be used to assist in estimating the uncertainty that
results from extrapolation.
A best‐estimate code contains all the models necessary to predict the important
phenomena that might occur during a loss‐of‐coolant accident. Best‐estimate code
calculations should be compared with applicable experimental data (e.g., separate‐effects
tests and integral simulations of loss‐of‐coolant accidents) to determine the overall
uncertainty and biases of the calculation. In addition to providing input to the uncertainty
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