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Isotopes & Radiation
Members are devoted to applying nuclear science and engineering technologies involving isotopes, radiation applications, and associated equipment in scientific research, development, and industrial processes. Their interests lie primarily in education, industrial uses, biology, medicine, and health physics. Division committees include Analytical Applications of Isotopes and Radiation, Biology and Medicine, Radiation Applications, Radiation Sources and Detection, and Thermal Power Sources.
Conference on Nuclear Training and Education: A Biennial International Forum (CONTE 2021)
February 9–11, 2021
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Nuclear Science and Engineering
Fusion Science and Technology
Notes on fusion
The ST25-HTS tokamak.
Governments around the world have been interested in fusion for more than 70 years. Fusion research was largely secret until 1968, when the Soviets unveiled exciting results from their tokamak (a magnetic confinement fusion device with a particular configuration that produces a toroidal plasma). The Soviets realized that tokamaks were not useful as weapons but could produce plasma in the million-degree temperature range to demonstrate Soviet scientific and technical prowess to the world.
Following this breakthrough, government laboratories around the world continued to pursue various methods of confining hot plasma to understand plasma physics under extreme conditions, getting closer and closer to the conditions necessary for fusion energy production. Tokamaks have been by far the most successful configuration. In the 1990s, the Tokamak Fusion Test Reactor at the Princeton Plasma Physics Laboratory produced 10 MW of fusion power using deuterium-tritium fusion. A few years later, the Joint European Torus (JET) in the United Kingdom increased that to 16 MW, getting close to breakeven using 24 MW of power to heat the plasma.
Simon A. Clément, Philippe M. Bardet
Nuclear Technology | Volume 199 | Number 2 | August 2017 | Pages 151-173
Technical Paper | dx.doi.org/10.1080/00295450.2017.1327254
Articles are hosted by Taylor and Francis Online.
Because of the complexity of the flow within light water reactor (LWR) cores, numerous small-scale phenomena locally influence heat transfer and critical heat flux (CHF). They include development of viscous and thermal boundary layers, interchannel mixing, spacer grid mixing, rod vibrations, or confinement effects such as the proximity of the walls or the influence of the gap between adjacent fuel bundles. LWR prototypical conditions are particularly harsh environments and limit measurements to quantities such as pointwise pressure drop and temperature, the latter resulting in global heat transfer and CHF correlations. The local phenomena mentioned above are embedded in these correlations, leading to inherent empiricism (and therefore conservatism). Validated computational fluid dynamics (CFD) codes and models can predict these phenomena, thus providing modelization tools of greater accuracy. However, major requirements for validation campaigns include the matching of validation and application domains and the deployment of mature and high-resolution diagnostics. For the latter, many are available for single-phase flows due to their predominance in several research fields. Furthermore, in the lower part of LWR cores, flow is single phase, and only this regime is considered in this paper. To circumvent the challenges of deploying diagnostics in LWR conditions, surrogate fluids are commonly used, enabling the measurement of velocity, temperature, pressure, or wall shear stress. A large number of single-phase tests with resolution adequate to validate CFD models have been conducted with air, steam, and water at moderate temperature and pressure. However, to date, with these fluids, the application domain defined by the Reynolds and Prandtl numbers has not been reached.
Four surrogate gases are proposed to match application and validation domains while allowing the deployment of a broad range of diagnostics: pressurized sulfur hexafluoride, xenon, cryogenic nitrogen, and highly pressurized air. By controlling their operating temperature and pressure, they allow matching prototypical Reynolds and Prandtl numbers while preserving the length scale, velocity scale, and timescale. This is achieved by reproducing the kinematic viscosity and thermal diffusivity of several nuclear reactor coolants. Furthermore, for single-phase conjugate heat transfer, a complete scaling analysis is performed for one pressurized water reactor fuel rod within a bundle under normal operating conditions. Electrically heated rods made of magnesium oxide and Zircaloy, combined with the proposed surrogate fluids, provide a close matching of conjugate heat transfer. Additionally, the use of these surrogates offers a significant decrease of the heating and pumping powers. Single-phase heat transfer separate-effect tests can then be performed for the first time in a laboratory setup with one, or several, full-size fuel bundles at prototypical conditions, while allowing the deployment of a large range of diagnostics. Finally, existing test facilities for hydraulics and thermal hydraulics of prototypical fuel bundles can be utilized with minor retrofits, further facilitating test implementation.