Uncertainty Quantification in Reactor Safety: Time Dependency, Available Information, and Measurability

Abstract

Uncertainty Quantification (UQ) in the analysis of reactor safety is challenging. The power of UQ derives from its grounding in probability theory.1 But, certain important safety related events are not probability–measurable which is problematic for risk– analytic methodologies that rely on UQ computations. In this note we identify why the dynamics of available engineering information plays an essential role in governing the fidelity of uncertainty quantification, and why uncertainty quantification in reactor safety is limited by the un-measurability of certain critical events. We provide an historical example providing a practical context for our observations. Finally we discuss the implications of measurability for regulatory decision–making governed by recent nuclear industry legislation that advocates increased use of risk informed, performance–based regulation for advanced reactor licensing.