堆芯熔融物被牺牲性材料稀释后的热物性计算

在压力容器内滞留熔融堆芯的过程中，应用牺牲性材料的堆芯熔融物稀释方案是先进轻水堆中一种新型的严重事故缓解措施。当堆芯熔融物被牺牲性材料稀释后，会形成三元或三元以上的熔融混合物。计算多元熔融混合物的热物性是进行牺牲性材料筛选、传热计算和评价稀释方案可行性的重要前提。本文比较了Fe₃O₄、TiO₂和Al₂O₃-3种候选氧化物牺牲性材料（OSM）的基本物性，并计算了熔融三元UO₂-ZrO₂-OSM混合物的密度、比热容、热导率和黏度。研究发现，为保证熔融结构发生翻转，需布置的Fe₃O₄材料的质量较大，而TiO₂和Al₂O₃材料的质量较小。混合物的比热容和热导率随着OSM添加量的增加而增大，而黏度随OSM添加量的增加而减小。混合物熔点T_c越小，在相同温度下混合物的黏性也越小。

Thermophysical Property Calculation of Core Melt Diluted by Oxide Sacrificial Material

Diluting the core melt with oxide sacrificial material (OSM) during in-vessel retention (IVR) is a newly proposed severe-accident-management strategy of advanced LWR. When severe accident occurs, the OSM is melted by the relocated core melt, resulting in the formation of a ternary liquid mixture of core melt and OSM in the corium. To select OSM and evaluate the heat flux on the vessel outer surface, and to assess the feasibility of the dilution design scheme, the thermophysical properties of the formed multi-component mixture should be obtained first. In this paper, the thermophysical properties of Fe₃O₄, TiO₂ and Al₂O₃ were compared. Density, specific heat, thermal conductivity and viscosity of the molten ternary mixture UO₂-ZrO₂-OSM were also calculated.The results show that to ensure the inverse stratification to occur, implying that the oxide layer locates on top of the metallic layer, the required minimum mass of Fe₃O₄ should be larger than that of TiO₂ and Al₂O₃. The specific heat and thermal conductivity of the ternary mixture increase with OSM mass, while the viscosity decreases as the mass of OSM increases. Moreover at a given temperature, the molten mixture with a lower melting point also has a smaller viscosity.