Ratings, risk assessment

THERP (NUREG/CR-1278), is used to estimate HEPs for a risk assessment. It provides error probabilities for generic tasks and describes the process used to modify these rates depending on the specific performance shaping factors (PSFs) involved in the task... 

It is wortli noting tluit design calculations for tlie sizing of relief systems (relief valves, headers, scmbbers and knock-out drums, etc.) are conservative in order to protect tlie integrity of vessels and relief systems. Tlie calculations used for risk assessments are tliose which most accurately describe the discliarge rate from tlie luizardous incident being modeled. 

The development of soil corrosivity assessment techniques has largely been due to the pipeline industry s requirements for better corrosion risk assessment and the reduction of pipeline failures. Corrosion in soil is a complex process and over the years several parameters have been identified as having a significant effect on the corrosion rate in a given soil. 

Absorbed lead is distributed in various tissue compartments. Several models of lead pharmacokinetics have been proposed to characterize such parameters as intercompartmental lead exchange rates, retention of lead in various pools, and relative rates of distribution among the tissue groups. See Section 2.3.5 for a discussion of the classical compartmental models and physiologically based pharmacokinetic models (PBPK) developed for lead risk assessments. 

PBPK and classical pharmacokinetic models both have valid applications in lead risk assessment. Both approaches can incorporate capacity-limited or nonlinear kinetic behavior in parameter estimates. An advantage of classical pharmacokinetic models is that, because the kinetic characteristics of the compartments of which they are composed are not constrained, a best possible fit to empirical data can be arrived at by varying the values of the parameters (O Flaherty 1987). However, such models are not readily extrapolated to other species because the parameters do not have precise physiological correlates. Compartmental models developed to date also do not simulate changes in bone metabolism, tissue volumes, blood flow rates, and enzyme activities associated with pregnancy, adverse nutritional states, aging, or osteoporotic diseases. Therefore, extrapolation of classical compartmental model simulations... 

The O Flaherty Model simulates the age-dependence of lead kinetics on such factors as absorption efficiency, excretion efficiency, uptake into bone and loss from bone, and partitioning between plasma and red blood cells. The model does not incorporate age, dose rate, or time dependence of lead accumulation in every organ (e g., kidney) because the complex patterns of lead accumulation in certain tissues are not known (O Flaherty 1991a) (see Section 2.4.1). However, the basic model structure allows for additional modules to be incorporated, depending on its intended use in risk assessment. For example, additional modules that are currently being developed are a pregnancy model and a model of net bone loss in older women and men. 

LaGoy P. 1987. Estimated soil ingestion rates for use in risk assessment. Risk Analysis 7 355-359. 

Exposure assessment is one of the most important steps in risk assessment. It is the process that predicts or estimates the amount of the substance under study that reaches the human body. To assess the exposure, it is necessary to define in detail the exposure pathway, the route of exposure, the concentration of the pollutant in the particular media, the contact rate, the frequency of exposure, and the population exposed (age, gender, and vulnerable population, among others). A general equation (Eq. 1) to determine the exposure dose is as follows ... 

The procedure described by Figure 10-1 is frequently abbreviated based on circumstances. If failure rate data on the applicable equipment are not available, then risk assessment procedures cannot be fully applied. Most plant sites (and even subunits within a plant) modify the procedure to fit their particular situation. 

The relevant changes in exposure rates are also of importance for predicting the behavior of Mangrove ecosystems and environmental risk assessment for their fate. 

Quantitative risk assessment (QRA) The systematic development of numerical estimates of the expected frequency and consequence of potential accidents associated with a facility or an operation. Using consequence and probability analyses and other factors such as population density and expected weather conditions, QRA estimates the fatality rate for a given set of events. 

---