Design and analysis of passive residual heat removal system for a new MW-class compact nuclear power system

The heat pipe-cooled reactor is an ideal power source for unmanned underwater vehicles (UUVs) due to its compact design, simple structure, and high safety features. However, a heat sink loss accident may lead to reactor damage, requiring a passive residual heat removal system (PRHRS) for emergency cooling. This study presents a novel compact heat pipe reactor with a PRHRS that uses natural circulation to cool the heat pipes' adiabatic sections. A steady-state CFD simulation optimized the geometry, and a transient analysis code was developed in FORTRAN and validated with CFD results. The findings show a sharp increase in fuel temperature immediately after the accident, followed by a decrease as natural circulation cools the reactor. Throughout the accident, component temperatures stayed within permissible limits, with the maximum fuel and heat pipe temperatures not exceeding 965.13 K and 972.5 K, respectively. No boiling occurred in the PRHRS cooling water. This confirms that the PRHRS effectively removes residual heat, ensuring reactor safety during both steady-state and accident conditions, and lays the groundwork for the design of new MW-class compact heat pipe reactors.