Physics-Informed Unit Commitment Framework for Nuclear Reactors

Nuclear reactors are often modeled as inflexible baseload generators with fixed downtimes and restrictive ramping limits. In practice, however, operational flexibility for a reactor is coupled with its fuel-cycle. A critical physics constraint arises from xenon poisoning, in which the buildup of the neutron absorbing xenon following a power ramp-down suppresses core reactivity, thereby limiting power maneuvers and reactor restarts. Existing power system models represent these effects using static constraints, neglecting the crucial dependence of xenon-induced inflexibility on the instantaneous state of a reactor core. This study offers a physics-informed unit commitment framework that embeds fuel-cycle dynamics into dispatch modeling. Our approach tracks the reactivity margin and enforces core-state-dependent constraints on allowable minimum generation and restart downtimes, while endogenously scheduling refueling outages. To demonstrate the formalism, we apply the framework to a representative nuclear fleet operating alongside high shares of renewable energy and storage. The results show that operational mode significantly affects system outcomes; flexible nuclear operation slows reactivity degradation, extends fuel-cycles by up to 10%, reduces renewable curtailment, lowers production costs, and delays the onset of refueling outages. These findings highlight the importance of fuel-cycle-aware flexibility modeling and provide a computationally tractable approach for assessing the role of flexible nuclear power in decarbonized grids.