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Hybrid Plants for Thermal Energy Production
Published in Dimitris Al. Katsaprakakis, Power Plant Synthesis, 2020
Table 4.11 summarizes the most appropriate metals and alloys for use in thermal processes. As seen in this table, the sodium–potassium alloy, for example, exhibits a melting point of –12.6°C and a boiling point of 785°C. The high difference between its melting and boiling point creates a respectively high temperature margin ΔT while remaining in liquid phase, increasing the potential sensible heat storage, according to Equation 4.113. Additionally, the low melting point practically eliminates the solidification risk, under low solar radiation availability conditions. Finally, the executed thermal process under high temperature leads to higher efficiency of the thermodynamic cycle. With these characteristics, the sodium–potassium alloy seems to be ideal for use as a heat transfer fluid (HTF).
Fast reactors
Published in Kenneth Jay, Nuclear Power, 2019
These two small reactors were followed in 1958 by a much larger one, called BR-5, which is rated at 5,000 kW(H) and is cooled by liquid sodium. BR-5 is being used to provide experience with sodium cooling and to test fuel elements proposed for much larger reactors. Though small compared with Dounreay and E.B.R.-II, it has some interesting features. The fuel used is plutonium oxide—BR-5 seems to be the first reactor to run on this fuel—in the form of thin knitting needles canned in stainless steel. It was not considered necessary to try to breed plutonium on a practical scale in the reflecting blanket, to the latter is made of nickel although it has an inner layer, next the core, of uranium. Control is by moving part of the nickel reflector, thus allowing neutrons to escape and reducing reactivity. Sodium is used in the primary cooling loop and sodium-potassium alloy in the secondary.
Coolant Materials
Published in C. K. Gupta, Materials in Nuclear Energy Applications, 1989
The advantage of potassium as a coolant over sodium is in its lower melting point. The other properties are less attractive. The physical and thermal properties of potassium are nearly the same. As to the chemical properties, potassium is more reactive than sodium. Naturally occurring potassium consists of two isotopes, containing about 93.10% 39K and about 6.88% 41K. The remainder, 40K, is a beta and gamma emitter with a long half-life and thus has a very low level of activity. Of the three isotopes, 41K is converted to a radioactive isotope upon neutron absorption. It converts to 42K, a beta and gamma emitter with a 12.40- half-life, which in turn converts to stable 42Ca. While 40K converts to 41K, which is susceptible as mentioned above, its natural abundance is so low that its contribution to activity is not important. Sodium-potassium alloys containing 40 to 90% of potassium are in the liquid state at room temperature. This essentially eliminates the necessity of having the heating systems to melt a liquid metal coolant prior to starting the reactor. An austenitic alloy containing 77.2% potassium has a minimum melting point of 261.5 K.
A Critical Review of Heat Pipe Experiments in Nuclear Energy Applications
Published in Nuclear Science and Engineering, 2023
Scott Wahlquist, Joshua Hansel, Piyush Sabharwall, Amir Ali
The usage of HP technology in terrestrial reactor systems did not begin until around the mid-1980s. Huebotter and McLennan, presented the first implementation of HPs into terrestrial reactors for a fast, pool-type fission reactor that utilizes a HP sodium-water heat exchanger.54 Hampel developed an underground nuclear power station concept using a self-regulating HP emplaced in the hole between the heat source and heat exchange near the surface of the Earth.55 Ohashi et al. presented preliminary studies on applying HPs in passive decay heat removal systems for modular High Temperature gas-cooled Reactors56 (HTRs). Kim et al. presented an update for the System integrated Modular Advanced ReacTor (SMART) on behalf of the Korea Atomic Energy Research Institute using HPs in the containment cooling system.57 Mochizuki et al. suggested using a HP cooling system for a boiling water reactor’s decay heat removal system.58 Wang et al. investigated a sodium HP (Ref. 59) and a sodium-potassium alloy HP (Ref. 60) for molten salt reactors’ passive residual heat removal systems. Jeong et al. presented a Passive IN-core Cooling (PINC) system, proposing a hybrid HP that combines HPs and control rods, allowing for direct decay heat removal and usage of the exact drive mechanism as control rods.61
Influence of Inclination Angle on the Start-up Performance of a Sodium-Potassium Alloy Heat Pipe
Published in Heat Transfer Engineering, 2018
Qing Guo, Hang Guo, Xiao Ke Yan, Fang Ye, Chong Fang Ma
Heat pipes play a significant role in meeting various requirements of engineering applications, including low-temperature, mid-temperature and high-temperature fields [[1–3], because of excellent heat transfer capacity through gas-liquid phase-change under a small temperature drop. High-temperature heat pipes, in which Li, Na, K [4, 5] are mostly considered as gas-liquid phase-change material (PCM), remain start-up problem from a frozen conditions [6–10]. This is because the melting points of mentioned alkali metals are higher than the ambient temperature, and thus results in a failure refluxing back to the evaporator section of the condensed solid PCM. Sodium-potassium alloy (Na-K), which is liquid at room temperature and pressure when the content of K in Na-K is wt. 46% to wt. 89% and has a similar thermal physical properties to Na and K, is recognized as one of promising alternatives to solve this technological problem for high-temperature heat pipes. In recent decades, Na-K heat pipes have received increasingly attractive for various engineering applications, such as thermal control for aero-engines [11], Stirling systems [12, 13], waste heat recovery system [14], molten salt reactor [15], isothermal furnaces [16], and gas turbine [17].
Conjugate MHD natural convection in a square cavity with a non-uniform heat source thick solid partition
Published in International Journal for Computational Methods in Engineering Science and Mechanics, 2022
Rabah Bouchair, Abderrahim Bourouis, Abdeslam Omara
In this section, numerical simulation results are presented to illustrate the effect of various controlling parameters on the flow and its thermal behavior such as the internal Rayleigh number RaI, the Hartmann number Ha, the solid heat source to fluid thermal conductivity ratio Kr, the thickness of the source solid partition Δ and the tilting angle of the cavity α. In addition, three values of Prandtl number Pr = 0.015, 0.024 and 0.054 corresponding respectively the mercury, gallium and sodium-potassium alloy are tested in order to choice an adequate metal liquid. These control parameters take, unless otherwise indication, the following values: Ha = 0, Kr = 1, Δ = 0.2, and α = 0.