Accurate nuclear cross-section sensitivity-coefficient evaluation is important for sensitivity and uncertainty analysis, similarity analysis, cross-section adjustment et al. A cross-section perturbation will affect the lattice-physics calculation results through the transport calculation directly and through the resonance calculation indirectly. The indirect effect was found to be important in some cases in the previous studies. To quantify the indirect effect on the lattice-physics calculation results for subgroup resonance calculation method, a sensitivity and uncertainty analysis code COLEUS was developed based the GPT-based method. The eigenvalue sensitivity to non-resonance nuclide cross sections was investigated. Numerical results show that in the traditional LWR, the sensitivity coefficients will be overestimated if implicit sensitivity is neglected. And in the BWR, the implicit sensitivity will become more important along with the temperature rise. But if resonance fission and resonance capture play a coequal role or the background cross section is big, the implicit sensitivity can be small.

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