Temperature feedback-induced power redistribution and hot-spot migration in neutronics–thermal coupling

Neutronics–thermal coupling affects not only global reactivity but also the spatial relationship between heat generation and thermal response in heterogeneous reactor systems. This work presents a mechanism-oriented analysis of temperature feedback using a unified finite-volume SP3–heat-transfer framework on a common computational mesh. Three benchmark configurations are treated as numerical experiments, while eigenvalue, flux, power-density, and transient comparisons provide solver verification. Diagnostic quantities are introduced to characterize fuel-region power peaking, power–temperature hot-spot separation, dominant hot-region mismatch, relative power-density redistribution, and transient response delay. Across the investigated cases, the maximum local temperature change is approximately 3.6–17.9 times the corresponding volume-averaged change obtained from the same solution, reflecting strong spatial localization rather than numerical error. The hot-region weighted-center metric is less sensitive than pointwise peak locations to local peak switching and remains qualitatively robust over the tested threshold range. In the TWIGL transient without thermal feedback, the maximum local temperature increment reaches the 50% response level 16.9 ms later than the total power. In the prompt-only limit, the time required to reach 2 times is only approximately 26% of that for the full delayed-neutron model, confirming the stabilizing role of delayed-neutron precursor dynamics. These results provide a quantitative interpretation of feedback-induced redistribution, hot-spot evolution, and finite-time coupled response.