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2025 ANS Annual Conference
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Chicago, IL|Chicago Marriott Downtown
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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
Miriam A. Kreher, Samuel Shaner, Benoit Forget, Kord Smith
Nuclear Science and Engineering | Volume 197 | Number 2 | February 2023 | Pages 279-290
Technical Paper | doi.org/10.1080/00295639.2022.2067739
Articles are hosted by Taylor and Francis Online.
The Frequency Transform method is used for the first time to efficiently model a multiple-second transient problem with Monte Carlo (MC). This is achieved by coupling MC with a time-dependent coarse mesh finite difference (TD-CMFD) diffusion solver. TD-CMFD presents a large advantage over commonly used point kinetics equations since it preserves spatial resolution during the transient and provides equivalence with the high-order method through nonlinear diffusion coefficients. As TD-CMFD computes time-dependent and spatially dependent neutronics information, it also computes frequencies that describe the rate of change of neutron and delayed precursor concentrations. These frequencies are used in MC shape function calculations as an approximation for the time derivatives. As the simulation proceeds, MC calculations update the multigroup cross sections, currents, and diffusion coefficients that are needed in TD-CMFD, and in turn, TD-CMFD updates the frequencies. Our results show the success of the Frequency Transform method in prescribed transient problems on the C5G7 geometry and on a fuel pin geometry. The Frequency Transform method showed significant improvement compared to the Adiabatic approximation, which does not use any frequency information in the MC calculation. The improvements in spatial resolution are shown to be a direct result of frequencies. Additionally, a study of how TD-CMFD’s nonlinear diffusion coefficients behave in time provides a first-of-its-kind study of how equivalence factors are impacted by transients.