Abstract:
Background Microreactors exhibit closely coupled neutronic-thermal-mechanical responses during operation, accompanied by highly non-uniform temperature distributions. Traditional on-the-fly cross-section generation methods, such as Doppler broadening in MCNP, are limited to the resolved resonance region and cannot handle temperature-dependent thermal neutron scattering laws (TSL), which are critical for thermal-spectrum systems.
Purpose To address this gap, this study aims to develop an on-the-fly TSL cross-section generation capability within MCNP based on statistical sampling, with a focus on thermal neutron scattering in high-temperature moderators such as ZrHₓ, and to enable high-fidelity neutronic-thermal coupling analysis in microreactor simulations.
Methods A statistical sampling approach was implemented for on-the-fly computation of thermal scattering cross-sections. Multi-temperature cross-section evaluations were carried out for hydrogen in ZrHₓ, comparing discrete and continuous TSL treatments. The method was macroscopically validated through keff calculations in TRIGA and TOPAZ reactors. Furthermore, integrated neutronic-thermal coupling simulations were performed using unstructured-mesh MCNP coupled with ABAQUS.
Results The developed on-the-fly cross-section method produces keff values in good agreement with those obtained using pre-generated offline libraries. The integration with unstructured particle transport in MCNP allows spatially precise accounting for temperature feedback in the moderator region.
Conclusions The new on-the-fly TSL capability enhances the accuracy of temperature-dependent neutronics modeling in thermal-spectrum microreactors. Coupled with unstructured meshing, it provides an essential foundation for high-fidelity multi-physics simulations of solid-state compact microreactors.
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