A dynamic safety margins estimation with a limited number of PWR large break LOCA simulations

The development of methodologies for Risk-Informed Safety Margin Characterization (RISMC) in presence of stochastic and epistemic uncertainties affecting the system dynamic behavior is one of the objectives of the Light Water Reactor Sustainability (LWRS) Program. In the present work, the characterization of safety margin uncertainties is handled by Order Statistics (OS) (with both Bracketing and Coverage approaches) to jointly estimate percentiles of the distributions of the safety parameter and of the time required for it to reach these percentiles values during its dynamic evolution. The novelty of the proposed approach consists in the integration of dynamic aspects (i.e., timing of events) into the definition of a dynamic safety margin for a probabilistic quantification of margins. The methodology is applied to a pilot case study of a TRACE model of a Large Break Loss of Coolant Accident (LBLOCA) occurring in the Zion Nuclear Power Plant (NPP).