Verification of the ability of safe activation of the isolated DHR loop of the ALLEGRO reactor in the event of an accident with complete loss of power

The development of the ALLEGRO gas-cooled demonstration reactor dates back to the early days of Generation 4 reactors. A more detailed conceptual design is currently being developed, which includes thermohydraulic studies of the reactor's safety features. One of the key components is the emergency residual heat removal system provided by the Decay Heat Removal loop.

The proper operation of the DHR loop in a total loss of supply accident is strongly dependent on the initial phase of the accident, when helium stagnating throughout the loop volume creates a barrier to the start of its natural circulation in the loop.

This paper analyze in detail the 3D behavior of the isolated DHR loop both during the normal reactor operation and the operability of the system during the defined accident conditions. The results of the study confirm that the DHR system is designed to be able to safely start the reactor cooling process using natural circulation upon its activation and subsequently cool the hot helium continuously using the DHR exchanger.