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Bahn C.B.,Argonne National Laboratory | Majumdar S.,Argonne National Laboratory | Harris C.,The United States Nuclear Regulatory Commission
International Journal of Pressure Vessels and Piping | Year: 2011

Leak rate testing has been performed using Alloy 600 tube specimens with throughwall flaws. Some specimens have shown time-dependent leak behavior at constant pressure conditions. Fractographic characterization was performed to identify the time-dependent crack growth mechanism. The fracture surface of the specimens showed the typical features of ductile fracture, as well as the distinct crystallographic facets, typical of fatigue crack growth at low Δ K level. Structural vibration appears to have been caused by the oscillation of pressure, induced by a high-pressure pump used in a test facility, and by the water jet/tube structure interaction. Analyses of the leak behaviors and crack growth indicated that both the high-pressure pump and the water jet could significantly contribute to fatigue crack growth. To determine whether the fatigue crack growth during the leak testing can occur solely by the water jet effect, leak rate tests at constant pressure without the high-pressure pump need to be performed. © 2011. Source


Yadav M.S.,Pennsylvania State University | Kim S.,Pennsylvania State University | Tien K.,The United States Nuclear Regulatory Commission | Bajorek S.M.,The United States Nuclear Regulatory Commission
International Journal of Multiphase Flow | Year: 2014

This study investigates the geometric effects of a 90-degree vertical-upward elbow on local two-phase flow-parameters in an air-water system, and develops an experimental database for interfacial area transport modeling. The experimental facility is constructed from 5.08. cm inner diameter acrylic pipes and includes vertical and horizontal sections interconnected by a 90-degree vertical glass elbow. The elbow has a radius of curvature of 15.24. cm and is installed at L/. D= 63 from the inlet. A four-sensor conductivity probe is used to measure time-averaged local two-phase flow parameters including: void fraction, bubble velocity, interfacial area concentration, and bubble frequency at ten axial locations along the test section. It is observed that the bubbles moving through the vertical-upward elbow are entrained by the secondary flow leading to a bimodal distribution in bubbly flow conditions. For the flow conditions investigated within the study, this bimodal distribution occurs regardless of the bubble distribution upstream of the elbow. It is found that the change in bubble distribution downstream of the elbow is strongly correlated to the dissipation of the elbow effects. Furthermore, the dissipation characteristics as well as the length of dissipation region for the vertical-upward elbow are found to be a strong function of the liquid-phase flow rate. © 2014 Elsevier Ltd. Source


Kim S.,Pennsylvania State University | Yadav M.S.,Pennsylvania State University | Talley J.D.,Pennsylvania State University | Ireland A.,The United States Nuclear Regulatory Commission | Bajorek S.M.,The United States Nuclear Regulatory Commission
Experimental Thermal and Fluid Science | Year: 2013

This study performs scaled separate-effects experiments to investigate the gravity-driven ingress of air into a helium filled vessel. Experiments are performed under both adiabatic and heated conditions up to 100. °C. An oxygen analyzer is employed to measure the transient oxygen concentration inside the test vessel during the ingress event. The air-ingress transient is found to be characterized by three distinct stages, namely: (a) The initial stage where the exchange flow rate linearly increases with time until it reaches its maxima and makes a transition; (b) The intermediate stage where the exchange flow rate decreases from its maximum value and varies non-linearly with time; and (c) The final stage of ingress where the exchange rate decreases asymptotically to zero towards the end of the ingress. An extensive oxygen concentration transient database is established accounting for various effects including the pipe-break size (or length-to-diameter ratios), break location, break orientation and the initial helium temperature. Predictive models are developed for the mixture density transient and the exchange flow rate during entire ingress process. Additionally, a non-dimensional critical density ratio is defined that determines the point of transition between the initial and the intermediate stages of the ingress process. © 2013 Elsevier Inc. Source


Yadav M.S.,Pennsylvania State University | Worosz T.,Pennsylvania State University | Kim S.,Pennsylvania State University | Tien K.,The United States Nuclear Regulatory Commission | Bajorek S.M.,The United States Nuclear Regulatory Commission
International Journal of Multiphase Flow | Year: 2014

This study develops a method to characterize the elbow-region for vertical-upward-to-horizontal air-water bubbly two-phase flows through a 90° elbow with a non-dimensional centerline radius of curvature, RC/. D, of three. The dissipation of the elbow-effects in the horizontal region downstream of the elbow is characterized by the change in the local void fraction distribution. To quantify the dissipation characteristics, the elbow-strength, S, is defined as the inverse of the second moment of the local void fraction distribution. It is found that the elbow-strength decreases exponentially with increasing development length in the elbow-region. The slope of decrease of the elbow-strength in the elbow-region is determined by the dissipation parameter, β. The dissipation parameter determines the development length required for the elbow-effects on the two-phase flow parameters to become negligible. It is found that the dissipation parameter is a linear function of the mixture Reynolds number for the flow conditions investigated in the present study. © 2014 Elsevier Ltd. Source

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