Neutronic-Thermal-Mechanical Coupling Transients Analysis of the KRUSTY 15 ¢ Warm Critical Experiment

Solid-state micro-reactors utilizing metallic nuclear fuel with high enrichment exhibit notable advantages including structural simplicity, high power density, and operational versatility. However, their compact core geometry combined with metallic fuel characteristics induces rapid neutron flux responses to external perturbations, resulting in distinct dynamic behaviors compared to conventional reactor designs. Accurate analysis of these dynamics requires concurrent consideration of thermal expansion effects and fuel Doppler feedback. This study formulates a neutronic-thermal-mechanical coupling methodology based on the Monte Carlo quasi-static dynamic framework, specifically addressing the transient analysis challenges in solid-state micro-reactors systems. The developed approach undergoes rigorous validation through benchmark comparisons with the KRUSTY space reactor's warm critical experimental data. Systematic simulations of 15¢ reactivity insertion transients under varying mechanical boundary conditions reveal critical insights into thermal feedback mechanisms. Key findings demonstrate that the dominant negative feedback in solid-state microreactors originates from geometry alterations induced by thermal expansion. Furthermore, the imposed mechanical constraints significantly influence simulation fidelity, particularly in capturing reactivity compensation effects during rapid transients.