Development of a plant dynamics computer code for analysis of a supercritical carbon dioxide Brayton cycle energy converter coupled to a natural circulation lead-cooled fast reactor.

Supercritical carbon dioxide cycle control analysis.

“…Previous analysis [2] demonstrated that the S-CO 2 cycle may not be suitable for removing heat from the reactor following reactor scram (i.e., removing the decay heat). It was previously found that a significant reduction of the heat removal causes the rapid decrease in the CO 2 temperature at the turbine inlet with subsequent reduction in the turbine outlet temperature.…”

“…Due to the recuperative nature of the S-CO 2 cycle, this reduction in turbine temperatures causes a decrease in the CO 2 temperatures at the main heat exchanger inlet, which in turn further reduces the turbine inlet temperature. It has been calculated [2] that if the S-CO 2 turbomachinery rotational speed is not controlled by the grid frequency (asynchronous mode), then the reduction in CO 2 temperature leads to reduction in turbine work below the required compressor work input in about 60 seconds such that CO 2 circulation cannot be maintained. If the turbomachinery continues to operate in a synchronous mode such that the compressors are run from the generator, than in about 400 seconds, the drop in CO 2 temperatures in the main heat exchanger lead to the freezing on the primary side coolant (molten Pb in Reference [2]).…”

“…It has been calculated [2] that if the S-CO 2 turbomachinery rotational speed is not controlled by the grid frequency (asynchronous mode), then the reduction in CO 2 temperature leads to reduction in turbine work below the required compressor work input in about 60 seconds such that CO 2 circulation cannot be maintained. If the turbomachinery continues to operate in a synchronous mode such that the compressors are run from the generator, than in about 400 seconds, the drop in CO 2 temperatures in the main heat exchanger lead to the freezing on the primary side coolant (molten Pb in Reference [2]). An attempt was made to adjust the cycle operating parameters, such as the turbomachinery rotational speed, for operation under the decay heat removal mode, but no acceptable solution (control scheme) was found which would enable long-term operation of the S-CO 2 cycle in this mode.…”

“…An important scenario which has not been previously calculated involves cycle operation for a SodiumCooled Fast Reactor (SFR) following a reactor scram event and the transition to the primary coolant natural circulation and decay heat removal. The Argonne National Laboratory (ANL) Plant Dynamics Code has been applied to investigate the dynamic behavior of the 96 MWe (250 MWt) Advanced Burner Test Reactor (ABTR) S-CO 2 Brayton cycle following scram. The timescale for the primary sodium flowrate to coast down and the transition to natural circulation to occur was calculated with the SAS4A/SASSYS-1 computer code and found to be about 400 seconds.…”

“…It is assumed that after this time, decay heat is removed by the normal ABTR shutdown heat removal system incorporating a dedicated shutdown heat removal S-CO 2 pump and cooler. The ANL Plant Dynamics Code configured for the Small Secure Transportable Autonomous Reactor (SSTAR) Lead-Cooled Fast Reactor (LFR) was utilized to model the S-CO 2 Brayton cycle with a decaying liquid metal coolant flow to the Pb-to-CO 2 heat exchangers and temperatures reflecting the decaying core power and heat removal by the cycle. The results obtained in this manner are approximate but indicative of the cycle transient performance.…”