Andrianova O.N.
A.I. Leypunsky Institute for Physics and Power Engineering, Obninsk, Russia
The improvement of nuclear data keeps pace with the improvement of methods and codes for reactor calculations; it is aimed at increasing the degree of detail of interactions between neutrons with nuclei. Recently, evaluated neutron data libraries have included information on nuclear data uncertainties to evaluate the accuracy of reactor calculations. The up-to-date IT capabilities make it possible to determine important neutronic parameters precisely, i.e., without any significant approximations reducing the accuracy of calculations. The main source of inaccuracy in precision neutronic calculations is neutron data. Therefore, it is extremely important to quantify the uncertainties caused by the neutron cross sections uncertainty. The paper discusses some methodological aspects of evaluating uncertainties in neutronic characteristics due to the resonance structure of neutron cross sections. The existing approaches to estimations of reactor functional uncertainties are described and compared taking into account the resonance structure of neutron cross sections (based on uncertainties both in the resonance self-shielding factors and resonant parameters). In addition, consideration is given to the ways of complementary use of statistical and deterministic techniques and the possibility of developing hybrid approaches on their basis. A description is made of the TUNEX software (Toolkit for Uncertainties Examination) based on MCNP for assessing the uncertainty of neutronic characteristics taking into account the resonance structure of neutron cross-sections in the group and point-wise representations of neutron cross sections. Finally, the results are presented of uncertainty evaluations for some fast reactor neutronic parameters (reactivity effects, reaction rates, etc.).
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