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Nuclear Nonproliferation Policy
The mission of the Nuclear Nonproliferation Policy Division (NNPD) is to promote the peaceful use of nuclear technology while simultaneously preventing the diversion and misuse of nuclear material and technology through appropriate safeguards and security, and promotion of nuclear nonproliferation policies. To achieve this mission, the objectives of the NNPD are to: Promote policy that discourages the proliferation of nuclear technology and material to inappropriate entities. Provide information to ANS members, the technical community at large, opinion leaders, and decision makers to improve their understanding of nuclear nonproliferation issues. Become a recognized technical resource on nuclear nonproliferation, safeguards, and security issues. Serve as the integration and coordination body for nuclear nonproliferation activities for the ANS. Work cooperatively with other ANS divisions to achieve these objective nonproliferation policies.
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2025 ANS Annual Conference
June 15–18, 2025
Chicago, IL|Chicago Marriott Downtown
Standards Program
The Standards Committee is responsible for the development and maintenance of voluntary consensus standards that address the design, analysis, and operation of components, systems, and facilities related to the application of nuclear science and technology. Find out What’s New, check out the Standards Store, or Get Involved today!
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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
Simon A. Clément, Philippe M. Bardet
Nuclear Technology | Volume 199 | Number 2 | August 2017 | Pages 151-173
Technical Paper | 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.