Feasibility Study for a Risk-Informed and Performance-Based Regulatory Structure for Future Plant Licensing, Volumes 1 and 2 (NUREG-1860)
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Manuscript Completed: December 2007
Date Published: December 2007
M. Drouin, NRC Project Manager
Office of Nuclear Regulatory Research
The purpose of this NUREG is to establish the feasibility of developing a risk-informed and performance-based regulatory structure for the licensing of future nuclear power plants (NPPs). As such, this NUREG documents a "Framework" that provides an approach, scope and criteria that could be used to develop a set of requirements that ould serve as an alternative to 10 CFR 50 for licensing future NPPs; however, this Framework is not the entire process. It is an initial phase in is to demonstrate the feasibility of such a concept, recognizing that for full implementation there will be outstanding programmatic, policy, and technical issues to be resolved. As such, this feasibility study does not represent a staff position, but rather a significant piece of research. The second phase, which involves implementation, is comprised of several, iterative steps: resolution of issues, development of draft requirements and regulations, pilots and tests, and rulemaking.
The information contained in this NUREG is intended for use by the US Nuclear Regulatory Commission (NRC) staff in developing requirements applicable to the licensing of commercial NPPs. Similar to 10 CFR 50, it covers the design, construction and operation phases of the plant lifecycle up to and including the initial stages of decommissioning (i.e., where spent fuel is still stored on-site). It covers the reactor and support systems. Fuel handling and storage are not addressed, but rather would be considered as part of implementation. The approach taken is one that integrates deterministic and probabilistic elements and builds upon recent policy decisions by the Commission related to the use of a probabilistic approach and mechanistic radioactive source terms in establishing the licensing basis.
At the highest level, the Framework has been developed from the top down with the safety expectation that future NPPs are to achieve a level of safety at least as good as that defined by the Quantitative Health Objectives in the Commission's 1986 Safety Goal Policy Statement. Criteria are then developed that utilize an integrated deterministic and probabilistic approach for defining the licensing basis and safety classification. Implementation of these criteria would require a design specific probabilistic risk assessment and would result in a design specific licensing basis. Defense-in-depth remains a fundamental part of the requirements development process and has as its purpose applying deterministic principles to account for uncertainties. Defense-in-depth has been defined as an element in NRC's safety philosophy that is used to address uncertainty by employing successive measures, including safety margins, to prevent or mitigate damage if a malfunction, accident, naturally or intentional caused event occurs. The approach taken in the Framework continues the practice of ensuring that the allowable consequences of events are matched to their frequency such that frequent events are to have very low consequences and less frequent events can have higher consequences. This is expressed in the form of a frequency-consequence curve. The allowable consequences are based upon existing dose limits, and the associated frequencies are based on guidance contained in International Commission on Radiological Protection 64 and engineering judgment.
Part of the process involves development of guidance to be used for actually writing the requirements. This guidance addresses writing the requirements in a performance-based fashion, incorporating lessons learned from past experience, and utilizing existing requirements and guidance, where practical. The guidance also ensures that the probabilistic process for establishing the licensing basis are incorporated. All of the above are integrated and results in a set of potential requirements which serve to illustrate and establish the feasibility of developing a risk-informed and performance-based licensing approach.
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