Probabilistic Multi-Hazard Assessment of Dry Cask Structures

Abstract

This study is focused on vertical concrete dry casks and their structural performance in seismic and tip-over events, aiming for risk estimation of large seismically induced motions (large sliding and tip-over) and structural damage due to the tip-over loads. Both numerical and experimental work was conducted to investigate the long-term performance of the concrete outerpacks with an exposed surface. Material level studies provided additional data to the existing literature on how to accelerate the corrosion and alkali-silica reactivity (ASR) in concrete without altering the key properties of the material to observe significant levels of deterioration in a short period of time. The developed methods are specifically geared towards large-scale applications of structural systems. Detailed thermal analysis was performed to determine the temperature distributions in both prototype and scaled casks. Tip-over experiments were performed on both intact and aged physical models of concrete casks to compare the structural performance in terms under combined aging and mechanical loading. The influence of shrinkage, creep and gravity loading in the long-term and combined ASR and tip-over impact were investigated using detailed numerical simulations. In the probabilistic assessments, the effect of different sources of aleatory and epistemic uncertainties on the structural performance of the dry casks are studied, and probabilistic models are developed for some of the key structural responses. Fragility curves are developed for seismic sliding motion and tip-over, as well as large acceleration in case of tip-over, and effect of different parameters' variations on the response is studied herein. Probabilistic seismic analysis on a portfolio of vertical concrete dry casks is performed in this study considering common cask configurations in the United States. Probabilistic seismic demand models for the maximum sliding distance and maximum angle of rotation of the casks are developed, and seismic fragility analysis and parameter study are performed. Seismic risk of large sliding motions and tip-over is estimated. In addition, finite element models are developed to analyze the structural response of a dry cask to impact tip-over loads considering the influence of material and structural parameter variations. Impact fragility curves are developed for the mean maximum acceleration of the cask in tip-over events, and effect of geometric and material properties on the response is investigated. 2 2 Volume V 3 3 Mass M 3 3 2.5. REFERENCES