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In this paper, a comparative analysis of loss of coolant accident (LOCA) in hot leg and cold leg of primary circuit in a VVER 1200 nuclear power plant is investigated. The effect of break size on the severity of the accident is observed. The break size was varied in the range 200-11350 cm2. For all the accident scenarios, station blackout (SBO) condition is set up. Additionally, it is assumed that no ECCS (Emergency Core Cooling System) is available due to system malfunction. The whole scenario is simulated in PCTRAN (Personal Computer Transient Analyzer) software. Results reveal that with the increase in the size of the break area, the core uncovering time decreases sharply. However, for a break size of 2800 cm2 or smaller, the water level in the core doesn’t drop to zero, indicating that the core is partially uncovered throughout the accident scenario. In case of hot leg LOCA, the draining of the reactor vessel is observed to be more rapid compared to cold leg LOCA, while the core melting started earlier in case of cold leg.

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Present study has been performed to understand condensation characteristics of argon vapor over nano-structured surface using non equilibrium molecular dynamics (MD) simulation. Main focus of this study is to explore the effect of condensation surface increment due to presence of nano-structure (considering flat surface as reference), solid-liquid interfacial wettability and condensation wall temperature. The simulation domain is a horizontal cuboid system that has two platinum walls at two opposite ends, left wall as the evaporation wall and the right wall as the condensation wall. Liquid argon was placed over the evaporation wall and the rest of the domain was filled with argon vapor. Various platinum nano-structured configurations were used to vary the surface area of the condensation wall. The system is first equilibrated at 90 K for a while and the evaporation of liquid argon is achieved by increasing the evaporation wall temperature at 130 K. The condensation of argon vapor is assumed for two different condensation temperatures such as 90 K and 110 K. The results indicate that condensation improves with condensation surface increment due to presence of nano-structure. Also it shows that the effect of condensation surface increment due to presence of nano-structure is drastically reduced with increasing solid-liquid interfacial wettability. The condensation at 110 K was poor compared to condensation at 90 K. The obtained results has been presented and discussed from macroscopic approach in terms of condensation mass flux, thermodynamic heat flux and time averaged wall heat flux.