Probabilistic modeling for fracture mechanic studies of reactor vessels with characterization of uncertainties

Abstract

The research presented in this paper addresses some important probabilistic fracture mechanics issues raised in recent efforts for assessing pressurized thermal shock risk (PTS) in pressurized water reactors (PWRs). The common objectives addressing these issues were to (1) provide a framework including uncertainty characterization and treatment for PTS studies; (2) use the screening criteria for scenario selection developed and reported by the authors; (3) develop a simple computation approach for PTS analyses; and (4) support other researchers in their efforts to develop tools and techniques for reactor vessel failure assessment.The PTS evaluation consists of three disciplines: probabilistic risk assessment, thermal hydraulics, and probabilistic fracture mechanics. The major contribution of this research has been to provide a framework for the fracture mechanics aspects of pressurized thermal shock analysis including uncertainty characterization and treatment. The uncertainty analysis proposed in this research makes a distinction between aleatory and epistemic uncertainties for proper propagation of uncertainties.To ease the computational burden incurred by introducing thermal hydraulics uncertainties, a simple and reasonably accurate fracture mechanics computational approach that performs fracture mechanics calculations rapidly and conservatively is proposed. The approach is tested by developing a mathematical routine in form of a simple Mathematica™ routine called MATH-PFM.