Robust PID control of power in lead cooled fast reactors: A direct synthesis framework

Highlights: • Power control in BREST lead cooled fast reactor is studied. • Coupled thermo-neutronic modeling of the core is taken into account. • PID control approach is resorted via the direct synthesis framework. • The controller robustness is investigated with regards to cycle burnup uncertainty. • Nyquist stability criterion has been employed for robustness analysis. - Abstract: Output core power control for an innovative design of lead cooled fast reactors (BREST) is investigated applying a PID design approach. The reactor core model is developed through a lumped parameter thermo-neutronic coupled layout of the plant. Control design is carried out within a direct synthesis framework whereby desired closed loop characteristics are incorporated. The PID coefficients are calculated employing a Laurent expansion of the intended controller and the resultant control scheme is employed on the uncertain nonlinear reactor plant. A worst case robust stability analysis is thereby conducted for the extreme hypothetical working point of the reactor subject to a near prompt criticality reactivity insertion. Results confirm that the control practice proposed may quite satisfactorily be implemented on the original plant as reasonable robustness characteristics are preserved for this ultimate operational point of the system. Nyquist stability criterion has been resorted for robust stability analysis with cycle burnup reactivity swing taken as the source of uncertainty and further recast into a multiplicative layout. The overall control method for desired power trajectories provides a safe reactivity insertion rate and a feasible rod speed.