# Consideration of heterogeneous effects in preparing multigroup neutron constants with the CONSYST/ABBN-RF system

12/05/2019 2019 - #04 Physics and technology of nuclear reactors

Andrianova O.N. Jerdev G.M. Lomakov G.B. Manturov G.N.

https://doi.org/10.26583/npe.2019.4.05

### UDC: 621.039.51.17

The need for developing mutually consistent calculation models for precision and engineering neutronic codes is defined by requirements to certification and verification of software and constants used for the neutronic calculations in accordance with the «Provision on Verification and Review of Software in the Field of «Neutron and Physical Calculations» (RB-061-11). The key requirement in RB-061-11 is that there shall be a methodically transparent and reproducible procedure to estimate the methodological and constant components of the calculation uncertainty to be implemented only if mutually consistent calculation models are available. Using an example of a series of measurements carried out on three critical BFS-61 configurations (JSC «SSC RF-IPPE n.a. A.I. Leypunsky»), factors are discussed which need to be taken into account when developing such types of models and the peculiarities of their application for calculating the neutronic characteristics of these BFS assemblies. Improved functional capabilities of updated neutron transport software and constants for the calculation and experimental analysis of the BFS integral experiments (ROSFOND/BNAB-RF, CONSYST and MMK-RF) have been demonstrated, allowing a much shorter time and the smallest possible probability of errors in preparing mutually consistent calculation models, as well as correct estimation of the methodological and constant components of the calculation uncertainty in accordance with RB-061-11. The results of estimating the constant uncertainty caused by group approximation are presented. It has been shown based on an analysis of the obtained results that the divergence in the calculations of the BFS-61 critical assembly configurations in the transition from the ROSFOND evaluated neutron data library to its group version, BNAB-RF, does not exceed 0.3% in criticality (a heterogeneous correction term of 0.2 to 0.8%). The estimated spectral index data bias falls within the limits of the Monte Carlo statistical uncertainty. Based on results of a calculation and experimental analysis for the entire set of measurements performed based on a series of the BFS-61 critical assemblies, the ROSFOND library is the nuclear data library providing minimal discrepancies between calculated and experimental values.

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integral experiments BFS effective neutron multiplication factor uncertainty Monte Carlo ROSFOND BNAB-RF spectral indices