The present paper systematically investigated pore scale thermal hydraulics characteristics of molten salt cooled high temperature pebble bed reactor. By using computational fluid dynamics (CFD) methods and employing simplified body center cubic (BCC) and face center cubic (FCC) model, pressure drop and local mean Nusselt number are calculated. The simulation result shows that the high Prandtl number molten salt in packed bed has unique fluid-dynamics and thermodynamic properties. There are divergences between CFD results and empirical correlations' predictions of pressure drop and local Nusselt numbers. Local pebble surface temperature distributions in several default conditions are investigated. Thermal removal capacities of molten salt are confirmed in the case of nominal condition; the pebble surface temperature under the condition of local power distortion shows the tolerance of pebble in extreme neutron dose exposure. The numerical experiments of local pebble insufficient cooling indicate that in the molten salt cooled pebble bed reactor, the pebble surface temperature is not very sensitive to loss of partial coolant. The methods and results of this paper would be useful for optimum designs and safety analysis of molten salt cooled pebble bed reactors.
The multiple effects of ecosystem restoration programmes deserve attention. After reviewing the social-ecological effects of 23 ecosystem restoration programs in Asia's drylands, we find that these programmes mainly contribute to sustainable development goals (SDGs) synergistically, but the trade-offs between social-ecological effects still exist. Among the five goals of SDG15 (Life on Land), SDG13 (Climate Action), SDG6 (Clean Water and Sanitation), SDG1 (No poverty), and SDG2 (Zero Hunger), 11 programs can synergistically achieve no less than three goals, especially grassland restoration and water diversion in China, as well as water management programmes in Israel. However, the contribution of ecosystem restoration programs to SDG15 easily weakens SDG6, SDG1, and SDG2, indicating the competition of land and water between ecosystem restoration and agriculture. To reduce the trade-offs among SGDs caused by ecosystem restoration, we propose the social-ecological system research framework of 'Dryland Boundary -Water, Food, Energy and Ecosystem Nexus -Meta-coupling -Nature-based Solutions' to guide the implementation of ecosystem restoration programmes from four aspects: supply-demand matching, element matching, regional matching, and local adaptation.
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