The combination of a hot fluid (e.g., molten metals) and a cold vaporizing fluid (e.g., water) can undergo spontaneous or externally assisted explosive interactions. Such explosions are a well-established contributor to the risk for nuclear reactors exemplified by the infamous Chernobyl accident. Once fundamentals are understood, it may be possible to not only prevent but also, more importantly, control the intensity for useful applications in the areas covering variable thrust propulsion with tailored pressure profiles, for enhancing rapid heat transfer, and also for powder metallurgy (i.e., supercooled powder production, wherein materials turn superplastic with enhanced ductility). This paper discusses results of experiments conducted with various molten metals, specifically, tin, gallium, galinstan, and aluminum interacting with water (with and without salt), and with and without noncondensable gases such as hydrogen or air. It is found that under the appropriate conditions, spontaneous and energetic phase changes can be initiated within milliseconds if the hot metal is tin or galinstan, including the timed feedback of shocks leading to chain-type reactions. Using 3–10 g of tin or galinstan, shock pressures up to 25 bars (350 psig) and mechanical power over ∼2-4 kW were monitored about 4 cm from the explosion zone. The interaction could be intensified more than ten folds by dropping the melt through an argon atmosphere. A slow metal quenching interaction occurring over tens of seconds could be turned explosive to transpire within milliseconds if the thermal states are within the so-called thermal interaction zone. Such explosive interactions did not transpire with gallium or aluminum due to tough oxide coatings. However, by adding ∼10 w/o of salt in water, molten Gallium readily exploded. It was also conclusively revealed that, for an otherwise spontaneously explosive interaction of tin-water or galinstan-water, the inclusion of trace (0.3 w/o) quantities of aluminum has a radical influence on stabilizing the system and ensuring conclusive prevention of explosion triggering. This paper compares and presents the results obtained in this study and draws analogies with industrial scale aluminum casthouse safety involving thousands of kilograms of melt. Insights are provided for enabling physics-based prevention, or, alternately, the intentional initiation of explosions.

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Tension metastable fluid states offer unique potential for leap-ahead advancements in radiation detection. Such metastable fluid states can be attained using tailored resonant acoustics to result in acoustic tension metastable fluid detection (ATMFD) systems. ATMFD systems are under development at Purdue University. Radiation detection in ATMFD systems is based on the principle that incident nuclear particles interact with the dynamically tensioned fluid wherein the intermolecular bonds are sufficiently weakened such that even fundamental particles can be detected over eight orders of magnitude in energy with intrinsic efficiencies far above conventional detection systems. In the case of neutron-nuclei interactions the ionized recoil nucleus ejected from the target atom locally deposits its energy, effectively seeding the formation of vapor nuclei that grow from the sub-nano scale to visible scales such that it becomes possible to record the rate and timing of incoming radiation (neutrons, alphas, and photons). Nuclei form preferentially in the direction of incoming radiation. Imploding nuclei then result in shock waves that are readily possible to not only directly hear but also to monitor electronically at various points of the detector using time difference of arrival (TDOA) methods. In conjunction with hyperbolic positioning, the convolution of the resulting spatio-temporal information provides not just the evidence of rate of incident neutron radiation but also on directionality — a unique development in the field of radiation detection. The development of superior intrinsic-efficiency, low-cost, and rugged, ATMFD systems is being accomplished using a judicious combination of experimentation-cum-theoretical modeling. Modeling methodologies include Monte-Carlo based nuclear particle transport using MCNP5, and also complex multi-dimensional electromagneticcum-fluid-structural assessments with COMSOL’s Multi-physics simulation platform. Benchmarking and qualification studies have been conducted with Pu-based neutron-gamma sources with encouraging results. This paper summarizes the modeling-cum-experimental framework along with experimental evidence for the leap-ahead potential of the ATMFD system for transformation impact on the world of radiation detection.

Tension metastable fluid states offer unique potential for radical transformation in radiation detection capabilities. States of tension metastability may be obtained in tailored resonant acoustic systems such as the acoustic tension metastable fluid detector (ATMFD) system or via centrifugal force based systems such as the centrifugal tension metastable fluid detector (CTMFD) system; both under development at Purdue University. Tension metastable fluid detector (TMFD) systems take advantage of the weakened intermolecular bonds of liquids in sub-vacuum states. Nuclear particles incident onto sufficiently tensioned fluids can nucleate critical size vapor bubbles which grow from nanoscales and are then possible to see, hear and record with unprecedented efficiency and capability [1]. Previous work by our group has shown the ability of TMFD systems to detect neutrons with energies spanning eight orders of magnitude with 95%+ intrinsic efficiency [2] while remaining insensitive to gamma photons and also giving directional information [3] on the source of the radiation. In this paper we describe research results with CTMFD systems for use in the detection of key actinide isotopes constituting special nuclear materials (SNMs) in spent fuel. Tests in a CTMFD system demonstrate the ability to detect alpha activity (at ∼100% efficiency) of U-isotopes at concentrations of ∼100 ppb (which is unprecedented and about x100–1000 more sensitive than from conventional liquid scintillation spectroscopy). An inherent capability of TMFD systems concerns on demand tailoring of fluid tension levels allowing for energy discrimination and spectroscopy. This appears especially useful to detect the key isotopes of U and other transuranic isotopes of Pu, Np, Am, and Cm that are at different stages of nuclear fuel reprocessing (i.e. UREX+).

Under appropriate thermal-hydraulic conditions the combination of a hot fluid (e.g., molten metals) and a cold vaporizing fluid (e.g. water) can be made to undergo spontaneous or externally assisted (e.g., via trigger shock) onset of explosive interactions (via destabilization of the interfacial vapor layer) and resulting in rapid heat transfer, phase change, pressure buildup and melt fragmentation. Energetic melt-water explosions are a well-established contributor to the risk of nuclear reactor systems such as the infamous Chernobyl Accident. The prevention of triggering of such interactions in nuclear systems is of paramount importance. However, once the fundamentals are understood, it may be possible to not only intensify but more importantly, to control the intensity of the interaction. The control and intensification of explosive interactions can become of considerable importance in the areas covering variable thrust propulsion with tailored pressure profiles, for enhancing rapid heat transfer, and also for powder metallurgy (i.e., supercooled powder production in which the resulting materials may turn super-plastic with enhanced ductility and strength). This paper discusses results of experiments conducted with various molten metals specifically, tin, galinstan and aluminum interacting with water, with and without non-condensable gases such as hydrogen. It is found that under the appropriate combination of conditions, spontaneous and energetic liquid water to vapor phase changes can be readily introduced within milliseconds if the hot metal fluid is tin or galinstan (but not for aluminum) including the timed feedback of shocks generated from earlier explosions leading to chain-type reaction fronts propagating through mixtures. Using 3–10 g metal masses of tin or galinstan spontaneously exploding in water, shock over-pressures up to 12 bar (175 psig) were monitored about 4 cm from the explosion zone, accompanied with mechanical shock power levels of about 2 kW. A previously slow phase change process (viz., normal metal quenching) occurring over tens of seconds could be turned explosive to transpire within milliseconds for melt-water thermal states within the so-called thermal interaction zone (TIZ). However, it was also conclusively revealed that, for an otherwise spontaneously explosive combination of tin-water or galinstan-water, the inclusion of even trace (0.3 w/o) quantities of aluminum which generates monoatomic non-condensable gas in the interfacial layer is found to have a radical influence on stabilizing the interfacial vapor layer between hot fluid and cold fluid, thereby ensuring conclusive (100% of time) prevention of explosion triggering for all cases tested. This paper compares and presents the results obtained in this study along with insights into energetics, with gram quantity melt droplets and draws analogies with data taken for industrial scale aluminum casthouse safety conditions involving thousands of kilograms of melt. Insights drawn for adaption to industrial settings are provided for enabling physics-based prevention or initiation.