Water ingress accident is one of the most severe accidents which must be analyzed in high temperature gas-cooled reactor pebble-bed modular (HTR-PM). The droplet could enter the primary circuit under the design basis accident of a double-ended guillotine break of a heat transfer tube. This paper simulates the behavior of single droplet evaporation and movement in the steam generator by numerical methods. Based on the structure characteristics of steam generator, the life time of droplet and the distance that the single droplet could move have been analyzed. The important parameters such as the droplet diameter, helium temperature, helium pressure and helium velocity which have an influence on the behavior of droplet evaporation and movement have also been discussed in detail.

The preliminary numerical simulation results indicate that the droplet diameter, helium velocity and helium temperature play an important role in the life time of droplet in the accident situation in the primary circuit. Helium pressure has a little effect on droplet evaporation in practical situation. The numerical simulation results demonstrate that only certain droplets with a diameter in certain range could arrive to the bottom of the steam generator pressure vessel (SGPV) and enter into the steam generator annular channel after collision with the bottom of the SGPV. The distance that the single droplet could move in the primary circuit is decided by a various complex factors such as the structure of the primary circuit, the droplet diameter and helium velocity. The preliminary analyses indicate that there is little probability for the single droplet to enter into the reactor core of the HTR-PM.

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