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High-temperature plumbing and advanced reactors
The use of nuclear fission power and its role in impacting climate change is hotly debated. Fission advocates argue that short-term solutions would involve the rapid deployment of Gen III+ nuclear reactors, like Vogtle-3 and -4, while long-term climate change impact would rely on the creation and implementation of Gen IV reactors, “inherently safe” reactors that use passive laws of physics and chemistry rather than active controls such as valves and pumps to operate safely. While Gen IV reactors vary in many ways, one thing unites nearly all of them: the use of exotic, high-temperature coolants. These fluids, like molten salts and liquid metals, can enable reactor engineers to design much safer nuclear reactors—ultimately because the boiling point of each fluid is extremely high. Fluids that remain liquid over large temperature ranges can provide good heat transfer through many demanding conditions, all with minimal pressurization. Although the most apparent use for these fluids is advanced fission power, they have the potential to be applied to other power generation sources such as fusion, thermal storage, solar, or high-temperature process heat.1–3
J. W. Coenen, B. Bazylev, S. Brezinsek, V. Philipps, T. Hirai, A. Kreter, J. Linke, G. Pintsuk, G. Sergienko, A. Pospieszczyk, T. Tanabe, Y. Ueda, U. Samm, The TEXTOR Team
Fusion Science and Technology | Volume 61 | Number 2 | February 2012 | Pages 129-135
Technical Paper | First Joint ITER-IAEA Technical Meeting on Analysis of ITER Materials and Technologies | doi.org/10.13182/FST12-A13378
Articles are hosted by Taylor and Francis Online.
Behavior and characteristics of tungsten materials under impinging high heat fluxes are investigated. Experiments with inertially - not actively - cooled samples have been carried out in the plasma edge of the TEXTOR tokamak to study the changes of material properties such as grain size and abundance of voids or bubbles. In addition, the effects of electron beam impact regarding subsequent W power handling have been studied in view of future devices.The parallel heat flux at the radial position in TEXTOR impinging on the plasma-facing components (PFCs) ranges around q[parallel] [approximately] 45 MW/m2 allowing samples to be exposed at an impact angle of 35 deg to 20 to 30 MW/m2. Melt layer motion perpendicular to the magnetic field is observed following a Lorentz force originating from thermoelectric emission of the hot W sample. Up to 3 g of molten W are redistributed forming hill-like structures at the plasma-connected edge of the sample. The typical melt layer thickness is 1.0 to 1.5 mm. Those hills are, due to the changes in the local geometry, particularly susceptible to even higher heat fluxes of up to the full q[parallel]; hence, locally the temperature of W can reach up to 6000 K, and thus boiling can occur.In terms of material degradation, several aspects are considered: formation of leading edges by redistributed melt, bubble formation, and recrystallization. Bubbles are occurring in sizes between 1 and 200 m while recrystallization increases the grain size up to 1.5 mm. The power-handling capabilities are severely degraded by all those aspects. Melting of tungsten in future devices is highly unfavorable and needs to be avoided especially in light of uncontrolled transients and possible unshaped PFCs.Predamaged samples from the TEXTOR exposures have also been exposed in the JUDITH 1 facility under transient heat loads (up to [approximately]1 GW/m2, energy impact: 36 MWm-2s1/2). The samples show an unfavorable increase in the ductile-to-brittle transition temperature. In addition, surface cracks lose their directionality recrystallizing toward a more isotropic state from the manufactured monodirectional state. The increased grain size leads to a more brittle behavior under transient thermal loads with respect to crack progression.
