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Improvements in Transport Calculations by the Energy-Dependent Fission Spectra and Subgroup Method for Mutual Self-Shielding

Pietro Mosca, Claude Mounier, Pierre Bellier, Igor Zmijarevic

Nuclear Science and Engineering / Volume 175 / Number 3 / November 2013 / Pages 266-282

Technical Paper

This paper shows two ways to improve the accuracy of the transport calculations. These improvements, implemented in the APOLLO2 code, concern the fission source calculation and the self-shielding models. The calculation of the fission source was generalized to fission spectra including an incident neutron energy dependence. The subgroup self-shielding model was updated for a mixture of resonant nuclides. Some tests on fast neutron systems like a critical sphere without reflector, a sodium-cooled cell, and a helium-cooled cell show that the use of four optimized incident macro groups for fission spectra guarantees a correct representation of the fission source.

The tests on a critical sphere with a thick steel reflector and on a water-moderated mixed oxide cell prove that the subgroup self-shielding, accounting for the mutual shielding of several resonant nuclides, allows us to improve the accuracy of the neutron transport solution.

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