With the natural circulation of water in the primary circuit, the flow rate increases as the power rises. There was a danger that this circumstance will restrict the rate of the MM power increase due to a slow increase of the flow rate to a new (increased) value or initiate the circulation instability.

Experiments have eliminated this possibility. In the case of a momentary raise of the power from initial values of 100, 300 and 550 kW by 200 kW, the set-up of a new flow rate value occures smoothly and readily (for < 1 min). Thus, the natural circulation is not a factor which could hinder providing the reactor with the necessary manoeuvre characteristics in the process of its operation as a part of a District Heat Plant.

2.2. Accident Regimes