Doppler effect evaluation of the TRU-based Moroccan TRIGA Mark II reactor: Applying novel methodologies

Abstract

The Doppler effect, commonly referred to as fuel temperature coefficient (${\alpha }_T$), is a critical parameter that quantifies the reactivity feedback resulting from changes in fuel temperature. Understanding and accurately quantifying ${\alpha }_T$ is essential for evaluating and adopting innovative fuel compositions. In this study, we present a comprehensive evaluation of ${\alpha }_T$ for transuranic (TRU)-based Moroccan TRIGA Mark II reactor, employing advanced simulation techniques and methodologies based on the OpenMC code. Two novel methods are introduced and validated. The first method analyzes the contributions of the fast fission factor ($ϵ$), resonance escape probability factor ($p$), thermal utilization factor ($f$), and reproduction factor ($\eta$) to ${\alpha }_T$. The second evaluates the Upscattering and isotope-wise contributions to gain deeper insights into the behavior of these factors. Additionally, ${\alpha }_T$ is evaluated as a function of fuel burnup. For comparative purposes, the standard U-ZrH_1.65 fuel is also analyzed to benchmark the behavior of the TRU-based fuel against conventional fuel types.

The results reveal that TRU-based fuel, despite its high fissile content, it maintains a negative ${\alpha }_T$ across the operational temperature range and throughout the reactor’s lifetime. This negative reactivity feedback is attributed to the significant thermal capture resonances of TRU-based isotopes, such ²⁴⁰Pu, and ²⁴²Pu, and the unique properties of the zirconium hydride matrix ZrH_1.65. Although the magnitude of ${\alpha }_T$ for TRU-based fuel is less negative compared to the standard U-ZrH_1.65 fuel, it remains sufficiently negative to guarantee safe reactor operation.

These findings are promising and suggest that further exploration of TRU-based fuels could support the development of reliable, clean, and sustainable nuclear energy systems.