Speaker
Description
The self-shielding effect in the unresolved resonance region has a large impact on the fast- and intermediate-spectrum reactors. The probability table method is widely used for continuous-energy Monte Carlo calculation codes to treat the effect. In this method, a table provides the probability distribution of the cross-section for a nuclide in the given energy grid points. The table is generated by averaging with a lot of “ladders” which represent pseudo resonance structures. Though many nuclear data processing codes require the number of ladders as an input parameter to generate the probability table, an optimal number of ladders has not been investigated. Our previous study revealed that the suitable number of ladders depends on the nuclide and its resonance parameters. This result indicates that it is very difficult for users to find the optimal number of ladders.
We developed the calculation method of the statistical uncertainty for the probability table generation. The product of the probability table and total cross-section in each probability bin is considered as the target of statistical uncertainty of the probability table. The central limit theorem (CLT) method, the Bootstrap method, and the Jackknife method are used to calculate the statistical uncertainty and the statistical uncertainties of these methods are compared. The calculation results indicate that the statistical uncertainty of the CLT method is similar to that of the other methods. The CLT method is the best way to calculate the statistical uncertainty of the probability table with a short computational time.
This statistical uncertainty calculation method for the probability table generation will be implemented in the next version of the nuclear data processing code FRENDY, i.e., FRENDY version 2. Users can generate the probability table with the optimal number of ladders when users set the criterion of the statistical uncertainty of the probability table as the input parameter.