Characteristics analyses on the coolant channel blockage of a pool-type lead-bismuth cooled small modular reactor utilizing natural circulation - 15472

Lead-bismuth eutectic (LBE) is a highly promising coolant for the Generation-IV (Gen-IV) reactor systems, and there are numerous technical activities to develop key technologies for lead-cooled fast reactors (LFRs) worldwide. In this situation, the Russian Federation is one of pioneers on LFR-related technologies, because they had 80 reactor-year of LFR operation experiences with ALFA-class nuclear submarines. However, these reactors suffered from coolant freezing problems during on-duty and that implies local blockage by coolant freezing would be a serious problem for the operation of an LBE-cooled reactor. Now that those submarine reactors were loop-type reactors, which is comprised of piping for the core cooling system, local blockage can impact whole reactor severely. To overcome this type of problem, a pool-type reactor called URANUS (Ubiquitous, Rugged, Accident-forgiving, Non-proliferating, and Ultra-lasting Sustainer) has been designed by NUTRECK (Nuclear Transmutation Energy Center of Korea). URANUS features natural circulation cooling systems for normal operation and in accident situations, and adopts large coolant channel in the reactor core region. Although employing large-sized channel, it could undergo a channel blockage accident and this would be led to a severe accident, under the natural circulation of coolant. To characterize the coolant channel blockage impact on URANUS core and system reaction, a thermal-hydraulic system analysis code MARS-LBE, originally developed by KAERI is used. The results of analyses show the excellent safety standard of URANUS and the importance of heat exchange in unblocked parts. The effect of cross flow at fuel assemblies makes heat transfer more stable and the increased mass flow rate of unblocked parts helps global heat transfer of this reactor