Structural Reliability: Probabilistic Fracture Mechanics
The PNNL-developed VISA computer code allows researchers to simulate the failure of embrittled reactor vessels associated with fabrication flaws and severe thermal shock transients.
Probabilistic fracture mechanics (PFM) and fracture analysis computer codes address the variability and uncertainties associated with stresses and loads acting on a vessel or piping component and the variability of the component to resist the imposing load. Researchers at PNNL are using their PFM expertise to assist the U.S Nuclear Regulatory Commission in making risk-informed decisions related to the structural safety of operating nuclear power plants.
Two computer codes developed and enhanced by PNNL researchers—PRAISE and VISA—address piping integrity concerns and embrittled reactor vessels associated with fabrication flaws and severe thermal shock transients. With PRAISE, researchers have applied this code extensively to life prediction and inspection issues associated with piping and have significantly enhanced the code modeling capabilities toward service-induced fatigue cracking, simulation of in-service inspections, and welding-induced fabrication flaws. In addition, the VISA code allows researchers to estimate the impact of fabrication flaws on the integrity of embrittled reactor pressure vessels.
PNNL researchers also are using data on ultrasonic detection and flaw-sizing capabilities to establish the effectiveness of weld inspection processes in reactor systems. Through collaborations with the Electric Power Research Institute at the EPRI Nondestructive Evaluation Center, researchers are statistically analyzing data from inspector qualification testing to develop probability of detection curves that will be used as input to PFM calculations. Such data allow PNNL researchers to estimate the capabilities of field inspector teams that perform ultrasonic weld inspections.
Through its continued research and development of PFM, PNNL is expanding the application of this modeling to statistical failures of automotive glazing, ceramic components of advanced fuel cell designs and vessels and piping in process industries.