Technical Needs for Enhancing Risk Monitors with Equipment Condition Assessment for Advanced Small Modular Reactors

Abstract

Advanced small modular reactors (aSMRs) can provide the United States with a safe, sustainable, and carbon-neutral energy source. The controllable day-to-day costs of aSMRs are expected to be dominated by operation and maintenance costs. Health and condition assessment coupled with online risk monitors can potentially enhance affordability of aSMRs through optimized operational planning and maintenance scheduling.Currently deployed risk monitors are an extension of probabilistic risk assessment (PRA). For complex engineered systems like nuclear power plants, PRA systematically combines event likelihoods and the probability of failure (POF) of key components, so that when combined with the magnitude of possible adverse consequences to determine risk. Traditional PRA uses population-based POF information to estimate the average plant risk over time. Currently, most nuclear power plants have a PRA that reflects the as-operated, as-modified plant; this model is updated periodically, typically once a year. Risk monitors expand on PRA by incorporating changes in the day-by-day plant operation and configuration (e.g., changes in equipment availability, operating regime, environmental conditions). However, population-based POF (or population-and time-based POF) is still used to populate fault trees. Health monitoring techniques can be used to establish condition indicators and monitoring capabilities that indicate the component-specific POF at a desired point in time (or over a desired period), which can then be incorporated in the risk monitor to provide a more accurate estimate of the plant risk in different configurations. This is particularly important for active systems, structures, and components (SSCs) proposed for use in aSMR designs. These SSCs may differ significantly from those used in the operating fleet of light-water reactors (or even in LWR-based SMR designs). Additionally, the operating characteristics of aSMRs can present significantly different requirements, including the need to operate in different coolant environments, higher operating temperatures, and longer operating cycles between planned refueling and maintenance outages. These features, along with the relative lack of operating experience for some of the proposed advanced designs, may limit the ability to estimate event probability and component POF with a high degree of certainty. Incorporating real-time estimates of component POF may compensate for a relative lack of established knowledge about the long-term component behavior and improve operational and maintenance planning and optimization.The particular eccentricities of advanced reactors and small modular reactors provide unique challenges and needs for advanced instrumentation, control, and human-machine interface (ICHMI) techniques such as enhanced risk monitors (ERM) in aSMRs. Several features of aSMR designs increase the need for accurate characterization of the real-time risk during operation and maintenance activities. A number of technical gaps in realizing ERM exist, and ...

An Updated Methodology for Enhancing Risk Monitors with Integrated Equipment Condition Assessment

“…Given the possibility of frequently changing demand in AdvSMRs, techniques to integrate advanced plant configuration information, equipment condition information, and predictive risk monitors are needed to support real-time decisions on O&M (Coble et al 2013). Essentially, enhanced risk monitors (ERM) are risk monitors that incorporate the time-dependent failure probabilities from prognostic health management (PHM) systems to dynamically update the risk metric of interest.…”

Local-Level Prognostics Health Management Systems Framework for Passive AdvSMR Components. Interim Report

“…The results of prognostic calculations should provide actionable information to influence O&M decision making. In nuclear power applications, the impact of prognostics can be felt by incorporating the results into enhanced risk monitors (ERMs), which provide time-dependent measures of risk of failure for individual systems or components and integrate these results into an overall risk metric for the reactor or plant (Coble et al 2013). v This report describes research results to date in support of the integration and demonstration of diagnostics technologies for prototypical AdvSMR passive components (to establish condition indices for monitoring) with model-based prognostics methods.…”

“…This is followed by the technical assumptions that bound the research described in the rest of this document. Additional details of AdvSMR concepts and likely O&M approaches are provided in the previous reports in this series associated with AdvSMR prognostics and enhanced risk monitor research (Coble et al 2013;Ramuhalli et al 2013b;).…”

Technical Report on Preliminary Methodology for Enhancing Risk Monitors with Integrated Equipment Condition Assessment

“…The functional requirements are described in detail in Coble et al (2013) and include the ability to:…”

“…Many approaches to estimating the failure probabilities at future times are available for nuclear power system components (Coble et al 2012;Coble et al 2013;Meyer et al 2013). A common approach involves characterization of the expected lifetime of an average system or component operating in an average environment, under average usage conditions.…”