3D analysis of spray effect on long-term depressurization of VVER-1000 containment during LB-LOCA

Containment as the last barrier of defence in depth strategy plays the most important role in protecting the environment and public from the release of radioactive material. As a result, analysing its performance in nuclear accidents and the reliability and effectiveness of its engineering safety features (ESFs) in the depressurization of containment is a key step in safety assessment. This study demonstrates the effect of the spray system as one of the ESFs in long-term depressurization of VVER-1000 containment during an LB-LOCA accident by using GOTHIC code. In the first step toward this goal, the as-built 3D structure of VVER-1000/V446 containment has been prepared in AutoCAD and used as GOTHIC geometry input by applying the input preparation process. Long-term 3D profiles of temperature and pressure were simulated in GOTHIC without spray actuation. The next step deals with considering the effects of spray and sensitivity analysis of spray temperature and droplet diameter on long-term depressurization. 3D profiles of thermal-hydraulic parameters during long-term depressurization of containment have been presented as research outcomes and validated against FSAR data and finally, the effects of spray on profiles were concluded. Results can obviously prove the effect of spray on the long-term depressurization of containment. The required time to achieve half of the peak pressure of the containment was calculated as 1380 s which is completely in agreement with NRC safety criteria. Research outcomes confirm the success of the spray system to support the integrity of containment which could be jeopardized without spray system intervention.