Optimal control of xenon-induced spatial power oscillations

Xenon-induced spatial power oscillations are a potential operating problem for present-day pressurized water and gas cooled reactors. An optimal control strategy for damping a one dimensional xenon-induced spatial power oscillation in a minimum time has been formally derived using Pontryagin's Minimum Principle. The lambda-mode method has been used as a primary tool in the spatial flux expansion. Compared with the previous natural-mode analysis, the current approach not only provides a greater potential for drawing theoretical conclusions but is also more practical in the sense that all of the terms in the control formulation are calculable and the derived control policies can readily be given a physical interpretation. Based upon simulation studies with the 3-D computer code NOXE3D, the optimal control strategies and remedial second switchings, as well as sub-optimal alternatives with bounded flux-tilt contraints, have all been demonstrated. Thermal feedback effects on xenon oscillations have been investigated both analytically and numerically with emphasis upon examining the different roles that fuel and moderator temperature feedback play during reactor transients. Control of the xenon transients triggered by maneuvering power changes during load-following operations has also been studied and simulated. Finally, two-dimensional modal cross-coupling is briefly discussed