Comparative Analysis of ATWS for OPR1000 by using RETRAN-3D and CESEC-III Codes

An Anticipated Transients without Scram (ATWS) is an anticipated operational occurrence accompanied by a failure of the reactor to trip when required. ATWS events are of concern since, under certain conditions (e.g., additional component and/or system failures) these could lead to unacceptable consequences up to and including core melt and release of radioactivity to the environment. The major concern of the ATWS derives from the consequences of the expected high primary system pressure, which is characteristic of this transient. RETRAN-3D is a best-estimate thermal-hydraulic transient code and is used as a system analysis code in the development of a non-LOCA safety analysis method for the future application to Optimized Power Reactor (OPR1000) design. A lot of efforts are now being made to investigate the applicability of the RETRAN-3D code especially to Non- LOCA analysis, by comparing the analysis results with those from the current licensing code, CESEC-III. The comparative simulations of Steam Line Break (SLB) and Locked Rotor event already showed that the RETRAN-3D code is applicable to the analysis of Non- LOCA events. However, ATWS analysis of OPR1000 using RETRAN-3D has not been performed. In this paper, detailed thermal hydraulic analyses for a loss of main feedwater event assuming that the DPS is not available in addition to the failure of RPS were performed using the RETRAN-3D code. To investigate the applicability of the RETRAN-3D to ATWS analysis of OPR 1000, the calculation results were also compared with those of CESEC-III