Transactions of the Korean Nuclear Society Virtual spring Meeting May 13-14, 2021 Program and Test Description of the Third Phase of OECD/NEA ATLAS International Joint Project

During the past three decades, a number of integral effect test (IET) facilities have been constructed and successfully operated around the world and they have been used to resolve the thermal-hydraulic safety issues and to validate the system-scale safety analysis codes. The overall system behaviors and the related phenomena during the accident transients can be investigated by performing a well-designed IET. In particular, an event that has an extremely low occurring frequency but results in high core damage frequency can be investigated by utilizing the IET from the viewpoint of the "defense in depth" concept. Within the context of the OECD/NEA ATLAS Phase 2 Project from October 2017 to December 2020, a series of tests were performed to resolve key thermal-hydraulic safety issues related to multiple high-risk failures and highlighted in particular from the Fukushima accident, by using the ATLAS (Advanced Thermal-hydraulic Test Loop for Accident Simulation) facility [1, 2]. These tests provided a unique database for validation of systemscale safety analysis codes and contributed to an understanding of thermal-hydraulic phenomena during the multiple high-risk failures covering the design basis accidents (DBAs) and beyond DBAs (BDBAs).