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Dry cask storage systems (DCSS) are widely used worldwide for storage of spent nuclear fuel (SNF). Particularly, in the United States, other than the SNF pools, DCSS are the only means for storage of SNF. In the United States, the DCSS are licensed for an initial 20 years (with a possible extension of 40 years). The absence of a long-term (or permanent) storage facility has brought up concerns regarding the long-term performance of DCSS, which may now have to be used for extended durations reaching over 100 years. The DCSS with an exposed concrete overpack account for approximately 61% of the DCSS inventory in the United States. The corrosion of the steel reinforcing bars (rebar) and the alkali-silica reactivity (ASR) of concrete have been identified as two of the main degradation mechanisms. In this paper, the accelerated aging of reinforced concrete (RC) overpacks of a vertical DCSS is evaluated experimentally at the structural scale. Three 1/3-scale specimens were fabricated. The first specimen was built using a conventional selfconsolidating concrete to serve as a control. The second and third specimens were prepared using special concrete mixtures, designed to accelerate the corrosion of rebar and ASR. All three casks were observed for 2 years for aginginduced deterioration using various non-destructive approaches including visual inspection, half-cell potential, Schmidt hammer, and ultra-sonic pulse velocity (UPV) measurements. The RC overpacks have been observed to exhibit significant distress due to these aging mechanisms. The overall conclusion is that accelerating ASR and corrosion through use of reactive aggregates and/or addition of chemicals (NaOH and CaCl 2 in this particular case) is a viable and practical approach for large-scale studies. Although accelerated aging of concrete structures have been extensively studied in the literature, this is one of the first studies on the long-term degradation in DCSS due to corrosion and ASR.

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The safety of the civil structures could be significantly improved against shock waves and blast loads by using steel concrete steel (SCS) protective walls. A numerical study has been performed to simulate the response of SCS wall subjected to a near-field blast load. A conventional SCS panel subjected to near-field blast load and its structural performance is evaluated in terms of maximum damage and deformation. The simulations performed using ABAQUS\EXPLICIT finite element package and built-in concrete damage plasticity concrete constitutive formulation. The maximum deformation, plastic strain, and failure mode under different loading scenarios have been investigated. The aim of this study is predicting the structural response of the SCS panel with different blast charge and identification of optimum configuration in terms of concrete strength and plate thickness. In the second part of the study, two novel sandwich configurations consisting of a corrugated metal sheet and the concrete core are proposed and compared with the conventional protective walls. The optimum parameters for each structural component are identified using an optimization procedure. Based on this study, using the proposed wall configuration will results in superior performance compared to the conventional walls while the extra cost of fabrication is insignificant.

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The lateral capacity of exterior concrete columns subjected to a blast load is the key factor in the building collapse probability. Due to potentially severe consequences of the collapse, efforts have been made to improve the blast resistance of existing structures. One of the successful approaches is the use of ultra-high-performance-concrete (UHPC) jacketing for retrofitting a building’s columns. The columns on the first floor of a building normally have higher slenderness due to the higher first story. Since an explosion is more likely to take place at the ground level, retrofitting the columns of the lower floors is crucial to improve a building’s blast resistance. Casting a UHPC tube around a circular reinforced concrete (RC) column can increase the moment of inertia of the column and improve the flexural strength. In this study, a retrofitting system consisting of a UHPC layer enclosed by a thin steel jacket is proposed to improve the blast resistance of buildings in service. Most of the previous research is focused on design aspects of blast-resistant columns and retrofitting systems are mostly based on fiber reinforced polymers or steel jackets. A validated finite element (FE) model is used to investigate the effectiveness of this method. The results showed significant improvement both at the component and building system levels against combined gravity and blast loading.

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