Dynamic Analysis of S-CO₂ Cycle Control With Coupled PDC-SAS4A/SASSYS-1 Codes

The ANL Plant Dynamics Code (PDC) for the analysis of supercritical carbon dioxide (S-CO₂) Brayton cycle power converters has been under development at Argonne National Laboratory for several years. It is the leading state of the art capability for modeling S-CO₂ cycles at the system level. The SAS4A/SASSYS-1 Liquid Metal Reactor Code System is the leading capability for modeling a SFR or LFR at the system level. The SAS4A/SASSYS-1 code combines reactor dynamics with thermal hydraulics calculations. Coupled together, the two codes allow users to carry out for the first time very detailed transient calculations of an entire plant incorporating a SFR with a S-CO₂ cycle energy converter, including simulation of both design and beyond-design events. The developed coupling approach utilizes the restart capability of SAS4A/SASSYS-1 and allows the data transfer between the two codes at each time step. The coupling approach is demonstrated by carrying out S-CO₂ cycle control calculations in which the entire plant follows a user-defined electrical grid demand scenario. The automatic control mechanisms on the S-CO₂ cycle side allow following of the load changes in the entire 0–100% range. On the reactor side, an autonomous (i.e., no deliberate control other than startup and shutdown) operation is assumed where the reactor power is adjusted by the internal reactivity feedbacks to match the heat removal rate by the balance-of-plant.