Advancing the safety design of heat pipe cooled reactors: a case study of lead liquid bath and monolith stainless steel core

Abstract Driven by the demand for compact, portable, clean, and environmentally friendly energy sources, heat pipe-cooled microreactors have gained increasing popularity and research interest. Over the past five decades, several design alternatives have been proposed. One of the most popular designs is the monolith stainless steel core structure. Others have sought to improve safety and efficiency by introducing liquid metal cores (Na/Pb) with promising superior safety and high energy output advantages. In this work, we advance the development of heat pipe-cooled reactors through a comparative case study of 300 kW monolith stainless steel (solid core) and a lead liquid bath (liquid core). A detailed comparative analysis was conducted to evaluate their neutronic and thermal performance. The Neutronic analysis was conducted using the SuperMC-CAS Monte Carlo code, while ANSYS (CFD) was used for thermal analysis. The results confirmed the feasibility of the stainless steel design and revealed the inherent advantages of the lead liquid core. Both cores exhibit sufficient excess reactivity to sustain reactor operation for 10 years without refueling. The lead liquid core enhances inherent safety, exhibits high negative reactivity feedback, and ensures a more uniform power distribution. Thermal analysis reveals that the lead liquid core maintains lower peak temperatures and gradients during normal operation and heat pipe failure, minimizing thermal stress and enhancing safety margins. This study affirmed the robustness of a proposed lead liquid core as a viable alternative to conventional designs providing enhanced safety and performance for heat pipe microreactors.