Limiting thermal stress is an important design objective for advanced reactors. Hierarchical control is an approach we have used to regulate hot-side temperature through the plant during operational maneuvers that would otherwise result in unwanted temperature swings.
The figure shows the case of a sodium fast reactor where individual lower level controllers maintain important process variables near design values while setpoints are coordinated at a higher level to meet electric demand. The second figure shows the plant temperatures as function of steady state load over the range of normal operation. It was calculated with the aid of a digital twin to solve for the actuator inputs that deliver on the desired temperatures.
An element of controller adaption is required to ensure robust tracking of setpoint values for the case, as here, where the control system design proceeds using plant models that are known to have uncertainties. This might take the form of design for disturbance rejection.