Validation of RCS depressurization strategy and core coolability map for independent scenarios of SBLOCA, SBO, and TLOFW

Abstract

Severe accident analysis for Small Break (SB), Middle Break (MB), and Large Break (LB) Loss-Of-Coolant Accident (LOCA), Station Black Out (SBO), Total Loss-Of-Feed-Water (TLOFW) was performed and effectiveness of Reactor Coolant System (RCS) depressurization strategies of OPR1000 was analyzed using MELCOR 1.8.6 code. Required injection flow rate has been derived using Core Exit Temperature (CET) information obtained from MELCOR calculation and a simple model and corresponding coolability map have been suggested to assist effective operator action. The depressurization strategies using secondary Atmospheric Dump Valve (ADV) for SBLOCA, pressurizer Safety Depressurization System (SDS) for SBO and TLOFW were introduced in 5 min since the initiation of Severe Accident Management Guidance (SAMG). Respective mitigation strategy employed leads to significant delay of the reactor pressure vessel failure and RCS pressure at Reactor Pressure Vessel (RPV) failure was lower than the SAMG target pressure of 2.86 MPa. Thus, possibility of High Pressure Melt Ejection (HPME) and impair of containment building is expected to avoid effectively. Using CET information obtained from MELCOR calculation, a simple model and a coolability map for the required injection flow rate were developed for recovery of core coolability. It is suggested that the coolability map based on MELCOR calculation results may provide decisive and intuitive information to operators for more effective safety management.

Enhanced critical heat flux with single-walled carbon nanotubes bonded on metal surfaces

“…Under improper transient conditions, physical penetration of the reactor by the molten material of nuclear fuels and structures is possible unless proper thermal and safety management is implemented. Thus, to delay and mitigate the potential thermal penetration, proper thermal safety management should be considered in terms of external vessel cooling on the outer vessel surface of the reactor [1]. The importance of thermal safety management is not limited to power reactor engineering, as the industrial fields of microchip cooling, computer cooling, boiling and refrigerating facilities, and thermal processors involving heat flow also require thermal management to secure the safety and sustainability of the integrated thermal devices and systems.…”

Effectiveness and adverse effects of reactor coolant system depressurization strategy with various severe accident management guidance entry conditions for OPR1000

“…Unless the RCS pressure decreases, the SITs, which are the only cooling source, cannot be injected for SBO and TLOFW cases. Our previous study reported general trends of the RCS pressure, water level of the core, CET, relocated debris mass, and accumulated oxidation energy during hypothesized severe accidents of the SBLOCA, SBO, and TLOFW [5]. For the SBLOCA, the same mitigation strategy of opening the ADV was applied.…”

“…In our previous study of severe accident analysis for OPR1000, the effectiveness of the severe accident mitigation strategy was investigated with the fixed SAMG entry condition of CET = 923K [5]. Although OPR1000 is an evolutionary type of CEOG PWR, the SAMG entry condition from the WOG PWR was employed.…”