Safety is central to the design, licensing, operation, and economics of nuclear power plants. As the current light water reactor fleet continues in service up to and beyond 60 years, there are possibilities for increased frequency of systems, structures, and components failures that initiate safety-significant events, reduce existing accident mitigation capabilities, or create new failure modes. Plant designers commonly “over-design” portions of nuclear power plants and provide robustness in the form of redundant and diverse engineered safety features to ensure that, even in the case of well-beyond design basis scenarios, public health and safety will be protected with a very high degree of assurance.
A systematic approach to the characterization of safety margins and the subsequent margins management options represent a vital input to the licensee and regulatory analysis and decision-making that will be involved. In addition, as research and development in the LWRS Program and other collaborative efforts yield new data and improved scientific understanding of physical processes that govern the aging and degradation of plant systems, structures, and components.
Research and Development Purpose and Goals
The purpose of the Risk-Informed Safety Margin Characterization (RISMC) Pathway research and development is to support plant decisions for risk-informed margins management with the aim to improve the economics and reliability and sustain the safety of current nuclear power plants over periods of extended plant operations. The goals of the RISMC Pathway are twofold:
Develop and demonstrate a risk-assessment method that is coupled to safety margin quantification that can be used by nuclear power plant decision makers as part of risk-informed margin management strategies.
Create an advanced RISMC Toolkit that enables more accurate representation of nuclear power plant safety margins.
One of the primary items inherent in the goals of the RISMC Pathway is the ability to propose and evaluate margin management strategies. For example, a situation could exist that causes margins associated with one or more key safety functions to become degraded; the methods and tools developed in this Pathway can be used to model and measure those margins. These evaluations will then support development and evaluation of appropriate alternative strategies for consideration by key decision makers to maintain and enhance the impacted margins as necessary. When alternatives are proposed that mitigate reductions in the safety margin, these changes are referred to as margin recovery strategies. Moving beyond current limitations in safety analysis, the RISMC Pathway will develop techniques to conduct margins analysis using simulation-based studies of safety margins.
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