Separation of aleatory and epistemic uncertainties in probabilistic assessments
Aleatory and epistemic uncertainties are typically separated in a two-staged nested Monte Carlo simulation approach, where the epistemic parameters are sampled in the outer loop, while the aleatory variables are simulated as part of the inner loop. However, this process of uncertainty separation may lead to misinterpretation of the results, particularly with respect to the confidence (i.e., lower and upper bounds) in the estimated probabilities.
Estimating external corrosion rates for buried piping
The integrity of buried piping is a significant concern in many industrial facilities, including nuclear power plants, where failure or leakage can have significant economic, environmental, and safety consequences. Unlike aboveground piping, assessing the degradation of buried piping is very difficult due to access restrictions. Fitness for service (FFS) assessment requires the estimation of corrosion rates and allowances over a given evaluation period.
In-reactor diametral creep of Zr-2.5Nb pressure tubes
The cold-worked Zr-2.5 wt% Nb pressure tubes (PTs) constitute the pressure boundary within the core of CANDU reactors. Each pressure tube carries the primary heat transport fluid (heavy water) and encloses a string of fuel bundles. The pressure tubes are approximately 6 m long, 104 mm in diameter, and have a wall thickness of approximately 4.2 mm. Understanding and predicting diametral creep in pressure tubes is vital for the lifetime management of CANDU reactors.
Supporting the degradation assessment of systems structures and components
Nuclear utilities collect a vast amount of in-service inspection data as part of periodic inspection plans and the detailed assessment and monitoring of various degradation mechanisms, such as fretting, corrosion, and creep. The development of data visualization tools allows the consideration of all of the in-service inspection data in the analysis, and hence supports a more comprehensive degradation assessment of systems, structures and components (SSCs).
Integrating equipment reliability into long-range planning
Generation Risk Assessment (GRA) is analogous to Probabilistic Risk Assessment (PRA), where a system reliability model (e.g., fault tree) is used to assess the operation of a power plant under various conditions. In GRA, the principal objective is to assess the impact of system and equipment unavailability and failures on the ability of the plant to produce power over time (as measured in megawatt-hours).
Analysis of fish impingement at the Pickering nuclear station
The primary objective of this study was to estimate the reliability of the fish diversion structure (FDS) (i.e., barrier netting) in reducing the total biomass (i.e., fish) impinged at the Pickering Nuclear Station. Because of uncertainties in measurement and data collection, the exact amount of total biomass impinged at the station is unknown.