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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
R. R. Romatoski, L. W. Hu
Nuclear Technology | Volume 205 | Number 11 | November 2019 | Pages 1495-1512
Technical Paper | doi.org/10.1080/00295450.2019.1610686
Articles are hosted by Taylor and Francis Online.
An important fluoride-salt-cooled high-temperature reactor (FHR) development step is to design, build, and operate a test reactor. The uncertainties of the coolant thermophysical properties range between 2% and 20%. This study determines the effects of these high uncertainties by incorporating uncertainty propagation in a thermal-hydraulic safety analysis for test reactor licensing. A hot channel thermal-hydraulic model, Monte Carlo statistical sampling uncertainty propagation, and a limiting safety systems settings (LSSS) approach are combined to ensure sufficient margin to fuel and material thermal limits during steady-state operation while incorporating margin for high-uncertainty inputs. The method calculates LSSS parameters to define safe operation.
The methodology is applied to two test reactors currently considered, i.e., China’s first Solid Fueled Thorium Molten Salt Reactor (TMSR-SF1) pebble bed design and Massachusetts Institute of Technology’s Transportable FHR prismatic core design; two candidate coolants, i.e., flibe (LiF-BeF2) and nafzirf (NaF-ZrF4); and forced flow and natural circulation conditions to compare operating regions and LSSS power (maximum power not exceeding any thermal limits). The calculated operating region accounts for uncertainty (2σ) with an LSSS power for forced flows of 25.37 0.72, 22.56 1.15, 21.28 1.48, and 11.32 1.35 MW for pebble flibe, pebble nafzirf, prismatic flibe, and prismatic nafzirf, respectively. The pebble bed has superior heat transfer with an operating region reduced 10% less when switching coolants and 50% smaller uncertainty than the prismatic. The maximum fuel temperature constrains the pebble bed while the maximum coolant temperature constrains the prismatic due to different dominant heat transfer modes. Sensitivity analysis revealed that (1) thermal conductivity and thus conductive heat transfer dominate in the prismatic design while convection is superior in the pebble bed and (2) the impact of thermophysical property uncertainties is ranked and should be considered for experimental measurements in the following order: thermal conductivity, heat capacity, density, and last, viscosity. Broadly, the methodology incorporates uncertainty propagation that can be used to evaluate parametric uncertainties to satisfy guidelines for nonpower reactor licensing applications, and its application shows that the pebble bed is more attractive for thermal-hydraulic safety. Although the method is developed and evaluated for coolant property uncertainties, it is readily applicable for other parameters of interest.