For a nuclear power reactor operating under forced circulation (FC) and natural circulation (NC) conditions, during transitions between these two types of circulation condition, nuclear reactivity fluctuation will occur due to sudden coolant flowrate change, and the reactivity fluctuation will in turn cause variation of nuclear heating power. In order to provide a more achievable and less costly approach for experimentally investigating transient thermal-hydraulic behavior of these transitions between NC and FC in nuclear power reactors, we designed and established an electrically-heated experimental loop. The established experimental loop has a heating section, whose heating power is controlled in real time and programmed to simulate the nuclear power variation caused by fuel and coolant temperature reactivity feedback. This experimental simulation is specifically implemented by coupling the point kinetics model with temperature measurements of the electrically heated experimental loop. In our study, reactivity feedback during both NC-to-FC transition and the reverse transition were simulated experimentally, and different reactivity compensation strategies were tested. The simulation results show that: in transitions from FC to NC, the decrease of power in initial stage of the transitions can restrain the fast increase of the fuel temperature; while in transitions from NC to FC, enough negative reactivity should be inserted as soon as the circulation pump is shut down, so as to avoid the nuclear power increase peak.

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