FEASIBILITY ASSESSMENT OF LONG-TERM COOLABILITY OF ADVANCED SMALL MODULAR REACTOR IN MULTIPLE MODULE CONFIGURATION

Abstract

An advanced design of Autonomous Transportable On-demand Reactor Module (ATOM) in small modular reactor (SMR) is under development lead by the Korea Advanced Institute of Science and Technology (KAIST) with multi-university participation in Republic of Korea. Designed thermal power is 450 MWth and total 4 to 6 identical modules are envisioned to install in a plant building. Due to the larger power rate of the ATOM compared to the worldwide competing SMRs, a more rigorous safety feature needs to be employed to achieve long-term coolability. As a part of the new safety feature, this study proposes a large inventory of centralized common pool (CCP), which is the first-of-kind design applicable for the SMR. To investigate its feasibility, long-term coolability of the ATOM was investigated through numerical analysis. In the proposed plant building configuration, each reactor module is installed in the dry cavity at underground level and shares the coolant inventory supplied by the CCP. Under the postulated accident scenarios such as station blackout or loss of coolant accident, the CCP is designed to supply the emergency coolant to the dry cavity by gravity. The long-term coolability of the reactor module by the CCP was evaluated under two conditions; with and without a sump to collect condensate originated from the boiled-off steam in the cavity. By analyzing the balance between the heat transfer and decay heat, the maximum time (grace period) upon which the reactor module can be cooled down successfully by the CCP was evaluated. In case that the sump was not considered, the results showed that the CCP could ensure the grace period of at least 3 days, which is generally required coping time for external response without the sump. On the contrary, with the designed sump the coolant inside the cavity remained constant and the grace period could be prolonged infinitely. This study highlights that the CCP configuration can play a key role in achieving an indefinite cooling capability for the advanced SMR design.