Impact assessment of upscattering on resonance calculation using improved ultrafine energy group method

• Published in: Annals of nuclear energy Vol. 49; pp. 114 - 121
• Main Authors: Akbari, M., Minuchehr, A., Zolfaghari, A., Khoshahval, F.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.11.2012
• Subjects: Effective cross sections; MOX thermal lattice; Thermal upscattering; Ultrafine energy groups; Thermal upscattering; MOX thermal lattice; Effective cross sections; Ultrafine energy groups
• ISSN: 0306-4549; 1873-2100
• DOI: 10.1016/j.anucene.2012.05.021

► Changing the upscattering energy from 0.625eV to 4eV causes a decrease of 1040pcm in Keff for MOX fuels. ► In UO2 fuels, Keff decreases about 120pcm. ► Effective group cross sections below 4eV are changed considerably. ► Fission reaction in thermal energy groups changes up to 20%. ► Pu-240 resonance in 1.05eV is mostly influenced. Thermal upscattering has considerable impact on the neutronic analysis of light water reactors. This phenomenon is more significant for reactors with advanced fuels having high plutonium content: Mixed Oxide (MOX) fuels. In this paper, a sensitivity analysis for the impact of upscattering boundary energy on the integral results of MOX and UO2 fuels in light water reactors is performed using WIMSD-5B code. For investigating the impact on the effective cross sections, a spectrum calculation code Microtrans is developed which employs an improved ultrafine group method. Moreover, the impact on the effective cross sections of important resonances of fuel nuclides in thermal and epithermal energy ranges is studied in detail. Calculation results show that changing the upsacttering boundary from 0.625eV to 4eV leads to more than 1000pcm decrease in Keff in MOX fuels due to large resonances of Pu isotopes in thermal energy range, while this impact is about 120pcm for UO2 fuels. In addition, thermal upscattering has significant impact on the effective cross sections below 10eV.