Abstract
Great interest is given now to advanced nuclear reactors especially those using passive safety components. The Westinghouse AP1000 Advanced Passive pressurized water reactor (PWR) is an 1117 MWe PWR designed to achieve a high safety and performance record. The AP1000 safety system uses natural driving forces, such as pressurized gas, gravity flow, natural circulation flow, and convection. In this paper, the safety performance of the AP1000 during a small break loss of coolant accident (SBLOCA) is investigated. This was done by modelling the AP1000 and the passive safety systems employed using RELAP/SCDAPSIM code. RELAP/SCDAPSIM is designed to describe the overall reactor coolant system (RCS) thermal hydraulic response and core behaviour under normal operating conditions or under design basis or severe accident conditions. Passive safety components in the AP1000 showed a clear improvement in accident mitigation. It was found that RELAP/SCDAPSIM is capable of modelling a LOCA in an AP1000 and it enables the investigation of each safety system component response separately during the accident. The model is also capable of simulating natural circulation and other relevant phenomena. The results of the model were compared to that of the NOTRUMP code and found to be in a good agreement.
Highlights
Nuclear energy is increasingly considered as an attractive energy source that can deliver an answer to increasing worldwide energy demands
Two direct vessel injection (DVI) nozzles are located in the upper downcomer and safety injection water from Core Make-Up Tank (CMT), accumulators, in-containment refueling water storage tank (IRWST), and containment sump is supplied through the nozzles
At t = 0 s, a break was initiated in the cold leg by opening the loss of coolant accident (LOCA) valve
Summary
Nuclear energy is increasingly considered as an attractive energy source that can deliver an answer to increasing worldwide energy demands. A model of the AP1000 was developed using RELAP/SCDAPSIM [5] to simulate the passive core cooling system components and to investigate the performance of the different passive safety systems during a small break loss of coolant accident (SBLOCA). The first three stages of the ADS are represented by three parallel pipes connected to the pressurizer upper head and each flow path has two motor valves in series whose action is controlled by an open trip and a close trip in the input deck. Two direct vessel injection (DVI) nozzles are located in the upper downcomer and safety injection water from CMTs, accumulators, IRWST, and containment sump is supplied through the nozzles These nozzles are modelled as valves, 650 and 750.
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