There is "high confidence" in the ability of structures, systems and components (SSCs) of Nuclear Power Plants (NPPs) to perform as designed during Design Basis Accidents. For Design Extension Conditions (DECs), the SSCs are required to perform as designed with "reasonably high confidence." A deterministic design method is proposed to address DECs' higher demands in new and existing CANDU NPPs. The deterministic method builds on the current requirements of applicable codes and standards and recommends more relaxed acceptance criteria. Nevertheless, a means to probabilistically evaluate built-in margins exceeding demand induced by a DEC would provide a measure of the confidence in a DEC-assigned structure or component performing its function. Therefore, a probabilistic method that estimates the probability of survivability for a structure or component when subjected to the demand induced by a DEC is proposed. The probabilistic method could be used to indicate whether there is a need for applying design modification to existing design features to address demands of seismic DEC. The mean, 5-percentile, and 95-percentile fragility functions of these SSCs are used. These fragility functions are typically developed to determine the High-Confidence-Low-Probability-of-Failure value associated with the contribution of a structure or component to the overall plant seismic risk. Sample cases for design features that were implemented in existing CANDU NPPs to address DECs are presented. Both the deterministic and probabilistic methods are applied to cases of Civil structures, passive Mechanical & Electrical components as well as active Control & Instrumentation components.
A new stochastic analysis is developed to estimate the response of multiple supported mdof secondary systems to dynamic loading. In the proposed stochastic analysis, the effect of the dynamic interaction between the secondary and primary systems is included. An outline for the theoretical formulation of the proposed stochastic analysis is presented. The assumptions adopted in the formulation are discussed. The dynamic interaction is shown to comprise two effects: the effect of the interaction forces arising at the attachment points, and the effect of the changes in the primary system properties resulting from the attachment of the secondary system. In addition, numerical examples are provided to demonstrate the validity of the proposed analysis.
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