Showing papers by "Jacopo Buongiorno published in 2014"

Micro- and Nanoscale Measurement Methods for Phase Change Heat Transfer on Planar and Structured Surfaces

Abstract: In this opinion piece, we discuss recent advances in experimental methods for characterizing phase change heat transfer. We begin with a survey of techniques for high-resolution measurements of temperature and heat flux at the solid surface and in the working fluid. Next, we focus on diagnostic tools for boiling heat transfer and describe techniques for visualizing the temperature and velocity fields, as well as measurements at the single bubble level. Finally, we discuss techniques to probe the kinetics of vapor formation within a few molecular layers of the interface. We conclude with our outlook for future progress in experimental methods for phase change heat transfer.

Plug Design for Deep Borehole Disposal of High-Level Nuclear Waste

Abstract: This paper focuses on the improvement of the longevity and robustness of materials for sealing and plugging the upper portion of a deep borehole used for permanent isolation of high-level nuclear waste. Analytical models of porous and laminar flows show that even when materials have low intrinsic permeability, micron-sized cracks and gaps between the plug and rock (formed via chemical reaction, shrinkage, osmotic consolidation, etc.) significantly diminish the plug’s sealing properties. On this basis, materials such as asphalt, traditional cements, and pure bentonite—which crack or shrink under certain conditions—are unfavorable. An ongoing test program has formulated expanding cement mixtures containing MgO to prevent such bypass flow. Furthermore, these findings support using stable, malleable, and low-permeability plug material (k ≤ 10-16 m2), such as a crushed rock (70%) and bentonite (30%) mixture. Alternative clays such as sepiolite could be blended with the bentonite to further reduce the p...

Micro- and Nano-scale Measurement Methods for Phase Change Heat Transfer on Planar and Structured Surfaces

Abstract: In this opinion piece, we discuss recent advances in experimental methods for characterizing phase change heat transfer. We begin with a survey of techniques for high-resolution measurements of temperature and heat flux at the solid surface and in the working fluid. Next, we focus on diagnostic tools for boiling heat transfer and describe techniques for visualizing the temperature and velocity fields, as well as measurements at the single bubble level. Finally, we discuss techniques to probe the kinetics of vapor formation within a few molecular layers of the interface. We conclude with our outlook for future progress in experimental methods for phase change heat transfer.

Experimental and Analytical Study of Exponential Power Excursion in Plate-Type Fuel

Abstract: This paper presents an investigation of transient heat transfer, which may occur in nuclear reactors with plate-type fuel during a reactivity initiated accident. Analytical solutions of the heat transfer equation were developed to describe the behavior of plate-type fuel and the MIT pool boiling facility during exponential power excursions governed by conduction heat transfer. Experimental results for non-boiling transient heat transfer tests are also presented and compared to the analytical solutions. Infrared thermometry was used to measure the temperature on the heater surface. The test matrix included exponential power escalations with periods τ as short as 5 milliseconds and water subcoolings ranging from 0 to 78 K. Heat transfer curves and effective heat transfer coefficients to water were measured. The experimental data confirm that the effective heat transfer coefficient decreases monotonically as 1/√τ, as expected from the analytical solutions.

Offshore Small Modular Reactor (OSMR): An Innovative Plant Design for Societally Acceptable and Economically Attractive Nuclear Energy in a Post-Fukushima, Post-9/11 World

Abstract: The potential for major gains in safety, physical protection and economics of nuclear energy exists through the development of a floating Offshore Small Modular Reactor (OSMR). This is a plant that can be entirely built (and decommissioned) as a floating rig in a shipyard, floated to the operating site (within 8–15 km of the coast), anchored in relatively deep water (i.e., ∼100 m), and connected to the grid via an underwater transmission line. The OSMR design presented here features innovative passive and indefinite emergency core and containment cooling systems that eliminate the loss of ultimate heat sink accident, thus decreasing the likelihood of severe accidents. Furthermore, the OSMR containment design and back-up venting procedures effectively eliminate the threat of serious land contamination, should a severe accident actually occur.© 2014 ASME

Spar-type platform design for the offshore floating nuclear power plant

Abstract: There exists the potential for substantial gains in safety, physical security, and economics for nuclear electricity supply through the development of an Offshore Floating Nuclear Plant (OFNP). Utilizing the most reliable and efficient construction techniques, this plant can be built from modular components in a shipyard as a partially submerged floating spar platform. The plant can then be floated to a site between 5 and 10 miles off the coast, moored in approximately 100-meter deep water, and connected to the grid via an underwater transmission line. The OFNP is designed to take full advantage of its environment to include passive cooling systems that eliminate the loss of ultimate heat sink accident, thereby decreasing the likelihood of severe accidents. The platform’s structural design, mooring system, and siting protect it against severe weather systems and render it immune to tsunamis and seismic activity. Furthermore, the OFNP containment design and venting procedures effectively eliminate the threat of serious land contamination, should a severe accident actually occur. The OFNP overall design builds on decades of offshore oil drilling experience and is derived from a shortened cylindrical spar platform. The platform has a skirt diameter of 75 m, a waterline diameter of 45 m, an operational draft of 48.5 m, and a total weight of about 38,200 tons when the skirt is empty. The spar design maximizes hydrodynamic stability, has been tested in various locations around the world in oil extraction, and offers significant protection to critical systems from external threats. The reactor containment is located below sea level and centered in a hull surrounded by seawater. This positioning offers both considerable physical security as well as unique opportunities in passive cooling. Watertight levels house safety critical systems (e.g. reactor, spent fuel pool, control room, battery room), the steam cycle, the condensate storage tank, and the desalination plant, whereas upper levels house important albeit non-critical components, such as the living quarters, a non-safety diesel generator, and the helipad. The OFNP design eliminates all concrete and most site preparation; therefore it can be deployed on a faster timescale than traditional terrestrial based plants. (author)

Mechanical Stresses Affecting Deep Borehole Disposal of High Level Nuclear Waste

Abstract: While extensive stress field data are available from crystalline rock boreholes drilled in France (Soultz), Germany (KTB), and the USA (Cajon Pass, Monticello Reservoir), Canada and Sweden, the data and methods used to analyze them have yet to be applied to very deep geologic disposal facilities. Typically, to alleviate the stress fields that are intensified in a borehole, muds (mixtures of clay and water) are a critical component and are widely used in the drilling industry. In the first portion of this paper, we review the available mechanical data and analysis methods. Based on the most applicable measurements (in Canada and Germany), we propose values of stress fields and rock properties to be used for generic assessment of deep borehole disposal. The minimum horizontal stress can be approximated as Sh=23.2D, the maximum horizontal stress as SH=43.1D, and the vertical stress as SV=27.5D, where the stresses are in MPa and D is depth in km. This analysis also incorporates the effect of thermal stresses (relieved) by the cool drilling mud. Using an average uniaxial compressive strength results (C=212 MPa) and conservatively neglecting the increase in strength of crystalline rock under polyaxial conditions, a stable borehole can be drilled to 4.55 km with mud density of 1020 kg/m3. This is based on a stability limit such that at the bottom of the hole, a significant portion of the wall (180°/360°) reaches a critical state of stress (i.e., experiences spalling). Using relations developed for shallow mines (which may be overly conservative) the spalled zone is estimated to have a radius that is approximately twice that of the borehole. To reach 5 km, the mud density should be raised to 1420 kg/m3, or be actively cooled (90°C) below the ambient temperature of the rock (∼135°C) at that depth.Copyright © 2014 by ASME